Principles and Techniques of the Examination of the Visual Sensory System

CLINICAL NEURO-OPHTHALMOLOGY96

PERIMETRY AND VISUAL FIELD TESTING

General Principles

Perimetry and visual field testing have been clinical diag-nostic test procedures for more than 150 years. Althoughinstrumentation and testing strategies have changed dramati-cally over this time, the basic principle underlying conven-tional perimetry has remained the same. Detection sensitivityis determined for a number of locations throughout the visualfield using a small target presented against a uniform back-ground. The loss of sensitivity at various visual field loca-tions serves as a noninvasive marker for identifying pathol-ogy or dysfunction of the visual pathways. The ability ofperimetry to provide helpful clinical information has beenresponsible for its long-term use as a diagnostic procedure.Because perimetry can provide information about both thelikely anatomic locus and disease process or processes forafferent system abnormalities, it remains a vital part of theneuro-ophthalmologic evaluation.

Perimetry and visual field testing fulfill several importantdiagnostic functions:

1. Early detection of abnormalities. Because many ocularand neurologic disorders are initially expressed as sensi-tivity loss in the peripheral visual field, perimetry is animportant factor in identifying early signs of afferent sys-tem dysfunction. Perimetry is typically the only clinicalprocedure that evaluates the status of the afferent visualpathways for locations outside the macular region.

2. Differential diagnosis. The spatial pattern of visual fielddeficits and comparison of patterns of visual field lossbetween the two eyes also provide valuable differentialdiagnostic information. Not only can this information behelpful in defining the location of damage along the vis-ual pathways, it can also assist in identifying the specifictype of disease that has caused the damage.

3. Monitoring progression and remission. The ability tomonitor a patient’s visual field over time is importantfor verifying a working diagnosis, establishing whethera condition is stable or progressive, and evaluating theeffectiveness of therapeutic interventions.

4. Revealing hidden visual loss. Perhaps the most impor-tant role subserved by perimetry is the ability to findafferent visual pathway loss that may not be apparent tothe patient. Changes in foveal visual function are typi-cally symptomatic. Peripheral vision loss, on the otherhand, can often go unnoticed, especially if it is gradualand monocular. Visual field screening of 10,000 Califor-nia driver’s license applicants was performed, and nearly60% of individuals with peripheral visual field loss wereunaware that they had any vision problem (109). Paradox-ically, even though a patient may be unaware of periph-eral visual field loss, it can significantly affect the perfor-mance of daily activities such as driving (109–112),orientation, and mobility (97).

Perimetry and visual field testing are therefore importantin identifying visual abnormalities that might not otherwise

be detected by either a history or other parts of a standardeye examination.

In this section, we present a brief description of the psy-chophysical basis for perimetry, the various methods for per-forming visual field testing, and some helpful guidelines forinterpreting test results. It is not intended to be a comprehen-sive treatment of perimetry, however, and the interestedreader is directed to several excellent sources for a moredetailed account of perimetric techniques and other relatedtopics (113–124).

Some form of visual field testing should be performed onall patients, particularly those at greater risk of having visualfield loss: (a) patients over the age of 60; (b) individualswith high myopia, elevated intraocular pressure, diabetes,vascular disease, systemic disease, family history of glau-coma or other eye disease, or other risk factors for develop-ment of ocular or neurologic disorders; (c) individuals withvisual symptoms or complaints, but minimal findings ontheir eye examination; and (d) individuals with significantproblems involving orientation and mobility, balance, driv-ing, night vision and related activities. It is not feasible ornecessary to perform a long quantitative visual field exami-nation on all patients. However, a confrontation visual fieldor brief tangent screen evaluation should be performed aspart of a standard neuro-ophthalmologic examination. Whenmore sensitive measurements of the visual field are needed,automated static perimetry or manual kinetic perimetry canbe performed.

Manual perimetry with the Goldmann perimeter has manyadvantages. Since the perimetric stimulus presentation isdone by a human, subjects can be cheered on or cajoled intoperforming. When the perimetrist senses subject fatigue, arest break is given. Unlike the fixed, 6� spaced grid of con-ventional automated perimetry, Goldmann perimetry hascustom test point locations along with improvisation ofstrategies based on coexisting findings. Specific explorationstrategies can be used for individual concerns. This allowsfor much more accurate mapping of defect shape. This canbe invaluable for the topographic localization of visual fielddefects. However, manual perimetry is less sensitive thanconventional automated perimetry and it may be more time-consuming. Its most severe limitation, though, is that manyperimetrists are not adequately trained (125). This may beworse than no perimetry at all.

Automated perimetry has had a dramatic impact on im-proving the quality of care for patients with ocular disorders.Automatic calibration of instruments, standardized test pro-cedures, high sensitivity and specificity, reliability checks(‘‘catch trials’’), and quantitative statistical analysis proce-dures are some of the many advantages of this method ofperimetry; however, there are also disadvantages of auto-mated perimetry, including prolonged test time, increasedcognitive demands, fatigue, and lack of flexibility for evalu-ating difficult patient populations. We believe that there isno single method of visual field testing that is best for allcircumstances and all patients. Automated perimetry is butone of many tools that the clinician can use to evaluate pe-ripheral visual function, and the various forms of visual fieldtesting should be regarded as complementary techniques,

PRINCIPLES AND TECHNIQUES OF THE EXAMINATION OF THE VISUAL SENSORY SYSTEM 97

the utility and appropriateness of which are determined bythe clinical circumstances and the question that is being ad-dressed. There is no single method of data representation,analysis procedure, visual field index, or other method ofevaluating visual field data that provides all of the essentialclinical information. It is important to consider all of theinformation available, including reliability characteristicsand the subjective clinical interpretation of the visual field.In addition, it should be kept in mind that although the testmay be automated, the patient is not. It is unreasonable tobegin an automated visual field test, leave a patient alone ina dark room, and expect the patient to remain alert, energetic,attentive, interested, and to maintain proper alignment andfixation throughout the test procedure. Some patients requireperiodic rest breaks, encouragement, and personal contactto perform visual field examinations in a reliable manner. Itis also important to insure that proper test conditions, refrac-tive characteristics, and other factors have been properlyestablished before initiating the examination. Visual fieldtesting can be a powerful clinical diagnostic tool when thesefactors are kept in mind.

Psychophysical Basis For Perimetry and Visual FieldTesting

The primary psychophysical concept underlying perime-try and visual field testing is the increment or differentiallight threshold. The increment threshold (Weberian contrast)is the minimum amount of light that must be added to astimulus (gdL) to make it just detectable from the back-ground (L). At very low background luminances, the amountof light needed to detect a stimulus is constant. At higherbackground luminances, the increment threshold increasesin direct proportion to the background luminance, e.g., adoubling of the background luminance requires a doublingof the stimulus luminance for detection. This relationship,which holds over a large range of background luminancelevels, is known as Weber’s law, in honor of the Germanscientist who initially described it (126).

The standard background luminance used by most perime-tric devices is 31.5 apostilbs (asb), or 10 cd/m2. This is inthe range of background luminance levels for which Weber’slaw is valid. There are several advantages to the use of thisbackground luminance level: (a) it is close to the ambientlighting conditions found in offices and waiting rooms, re-quiring a minimal amount of adaptation time; (b) the back-ground luminance is one that is comfortable for most pa-tients; (c) patients have the least amount of responsevariability at this background luminance; and (d) factors af-fecting the amount of light reaching the retina (pupil sizechanges, ocular media transmission loss, etc.) have an equaleffect on the background and stimulus luminance. Thus, overthe range of background illuminances for which Weber’s lawholds, these changes in retinal illumination will not affect theincrement threshold measure.

Increment threshold determinations are usually made at anumber of visual field locations during quantitative perime-try. For a normal visual field, the increment threshold variesas a function of visual field location. Visual field results are

usually represented in terms of sensitivity, the reciprocal ofthreshold (sensitivity � 1/threshold). At the 31.5 asb back-ground luminance, the fovea has the highest sensitivity andis able to detect both the dimmest and the smallest targets.Sensitivity drops rapidly between the fovea and 3� decreasesgradually out to 30�, and then drops off more rapidly againbeyond 50� (Fig. 2.11). The characteristic three-dimensionalrepresentation of the visual field sensitivity profile is oftencalled the ‘‘hill of vision’’ or an ‘‘island of vision in a seaof blindness.’’ In addition to eccentricity-dependent changesin the slope of the visual field profile, the temporal visualfield (to the right of the foveal peak) extends farther thanthe nasal visual field, and the inferior visual field extendsfarther than the superior visual field. The location of theblind spot, approximately 15� temporal to the foveal peak,is indicated in most representations by a darkened verticallyoval area.

Visual field sensitivity can be affected by many differ-ent stimulus attributes, including background luminance

Figure 2.11. Three-dimensional representation of the normal visual fieldrepresented as a hill of vision. Sensitivity is plotted as a function of visualfield eccentricity.


(113,115,127), stimulus size (113,115,128–130), stimulusduration (113,115,131), chromaticity (132–136), and otherfactors (113,115). Of these parameters, stimulus size is themost important for clinical perimetry. Next to stimulus lumi-nance, it is the most common method of adjusting the detect-ability of perimetric stimuli. Not only does a change in stim-ulus size affect the overall sensitivity to light, but the slopeof the sensitivity profile is also changed (113,115). Smalltargets produce steeper sensitivity profiles, and larger targetsresult in a flatter sensitivity profile, especially for the central30–40� eccentricity. Response variability is also reduced asstimulus size is increased (130).

Certain patient characteristics that are not associated withocular or neurologic pathology can also influence the incre-ment or differential light threshold. Blur and refractive error(137), media opacities such as cataract (138), ptosis (139),and pupil size (140,141) can affect visual field sensitivitycharacteristics. In addition, procedural circumstances relatedto trial lens rim obstructions (142), fixation instability (143),response errors (144–146), and other artifacts of testing canproduce the appearance of visual field loss or can obscurevisual field deficits that are actually present.

Cognition, attention, and other higher-order functions inpatients undergoing visual field testing can influence visualfield sensitivity, as well as attention, practice, and learning(147–151). Fatigue effects can reduce visual field sensitivity(152–154), particularly after the test procedure has takenmore than 5–7 minutes of testing. Patients with visual fieldloss typically demonstrate greater fatigue effects than thosewith normal perimetric function, and this may be especiallytrue for some conditions such as optic neuritis (155,156).

Techniques For Perimetry and Visual Field Testing

Visual field examinations have been conducted for over150 years and, as a consequence, a variety of proceduresand techniques have been developed. Perimetry and visualfield test procedures may be categorized in several differentways: (a) the amount of information obtained by the test,i.e., screening versus quantitative; (b) the type of stimulusused to perform the test (kinetic, static, or suprathresholdstatic); and (c) the manner in which the test is administered(manually vs. computer-driven). There are both advantagesand disadvantages for each method. Automated perimetry,for example, provides greater standardization, calibration,and statistical analysis of results than manual visual fieldtesting, but it is less efficient, less flexible, and too demand-ing for some patients. Kinetic perimetry, when performedappropriately, is a more efficient method of performing anevaluation of the full visual field than static perimetry andthe technique can yield exquisite information about defectshape, but the technique varies from one test to another.Quantitative procedures provide a better ability to detect sub-tle anomalies and monitor changes over time, but they aremore time-consuming than screening procedures and maycause fatigue in some patients.

Confrontation Visual Fields

Confrontation visual field examination is rapid, reliable,and easy to perform. It is tailored to the clinical situation.

Most examiners test patients monocularly using double si-multaneous finger counting to survey the visual field for anydense quadrantic defect. Finger counting is followed by atest of the central visual field to evaluate for the presenceof relative visual field defects. One such test is to have thesubject look at the examiner’s face and report any differencefrom the expected. Another is to use two red objects andcompare perception of the two eyes or parts of the visualfield. Unfortunately, for optic nerve-related visual field de-fects, finger confrontation identifies only about 10% of de-fects while bedside color techniques yield defects in aboutone-third of patients with abnormalities on formal perimetry(157). Color confrontation techniques fare better with chias-mal defects, detecting about three-quarters of patients (157).Even by combining seven confrontation visual field tests,only about half of perimetrically identified defects are found(158). Therefore, formal perimetry is usually necessarywhen the patient has visual loss not explained by a generalophthalmologic examination.

Confrontation visual field techniques for infants and chil-dren can be quite challenging (Fig. 2.12). Because of theiradaptive abilities, children may demonstrate good mobilityskills and fool the examiner as to the extent of visual fieldloss. For infants and young children, a visually mediatedstartle response can be used to detect hemianopic defectsand other substantial defects in the peripheral field. A childwho sees a startle stimulus will look in that direction. Forolder children, finger mimicking or a ‘‘Simon says’’ gamecan be used to evaluate the peripheral visual field. The childmimics the examiner by holding up the same number offingers he or she observes. ‘‘Finger puppet perimetry’’ canbe performed, with one puppet used to direct central fixationand the other puppet used as a peripheral stimulus for sac-cadic eye movements. A story with dialogue between thepuppets is used to redirect attention from one puppet to theother.

In many instances, simultaneous comparison of color satu-ration or brightness of stimuli between hemifields or be-tween the two eyes is useful in distinguishing subtle anoma-lies. When the stimuli are presented in a double simultaneousfashion to the right and left of fixation, it is possible to detecthomonymous defects. Subtle deficits across the vertical mid-line can be detected by asking the patient to indicate whichof the two test objects is clearer or brighter. In addition,double simultaneous presentation can be used to detect thephenomenon of visual extinction—the lack of awareness ofan object in a seeing area of the visual field when otherseeing areas of the visual field are stimulated simultane-ously. Confrontation visual field testing is also useful inevaluating patients suspected of having nonorganic visualfield loss (11).

The obvious advantages of confrontation visual field test-ing include its simplicity, flexibility, speed of administra-tion, and ability to be performed in any setting, including atthe bedside. The disadvantages of confrontation visual fieldtesting include the lack of standardization, the qualitativenature of the results, and the limited ability to detect subtledeficits and monitor progression or remission of visual loss.Because it is quick and easy to perform, confrontation visual


Figure 2.12. Examples of confrontation visual field testing in childrenusing the startle response (a); finger counting (b); and finger puppets (c).

field should be performed on all patients, regardless of theirvisual complaints.

Amsler Grid

Mark Amsler developed a series of charts, specificallydesigned to qualitatively analyze the disturbances of visualfunction which accompany the beginning and evolution ofmaculopathies. The charts are a series of lined and patternedgrids that test the central visual field within 10� of fixationwhen the plates are held at 1/3 of a meter from the eyes(159). Each square of the grid subtends 1� of visual angle,making the ability to define the location of small defectsrather easy. The patient is asked to fixate a central spot onthe grid, using one eye at a time, and is asked if he or shecan see the spot. If not, the patient’s finger can be placedon the center to help fixation. The patient is then asked topoint out any regions in which the lines are missing, blurred,distorted, bent, or irregular.

This technique is well known to ophthalmologists whoroutinely examine patients with known or suspected maculardisease, because Amsler grids can be used to identify andplot small scotomas and other visual field defects that occurwith macular scars, mild macular degeneration, central ser-ous chorioretinopathy, and related disorders. It is perhapsless well recognized that small central or paracentral scoto-mas that occur with optic nerve disease can also be identifiedwith these plates. The Amsler grid (Fig. 2.2) is particularlyuseful for identifying small central scotomas and other subtlecentral visual disturbances that are difficult to detect withmore sophisticated automated and manual perimeters. Here,patients report missing areas rather than metamorphopsia.The grid can be dimmed in various ways to increase thesensitivity of detection of these small scotomas (160). TheAmsler grid is very quick and easy to administer. Its maindisadvantages are related to the qualitative, subjective natureof the information derived from the test.

Tangent (Bjerrum) Screen

The central visual field can be studied in detail using atangent or Bjerrum screen. The screen is made of black feltor other black matte material and can be mounted on the wallor hung from the ceiling. The screen has several concentriccircles and radial lines imprinted on it to provide a referencefor the examiner. A dark wand with circular targets of var-ious sizes and colors mounted on the end is used to examinethe central visual field, usually within 30� of fixation. In itsmost common application, testing is performed at a distanceof 1 meter, and a light source is employed to provide arelatively uniform illumination of 7 foot-candles on thescreen. Targets are specified in terms of their diameter, theircolor, and the testing distance in millimeters. For example,a 1-mm-diameter white target used with the patient located1 meter from the tangent screen would be designated as 1/1000W, and a 5-mm red target used with the patient located2 meters from the screen would be designated as 5/2000R.

A kinetic technique is usually performed to test the visualfield during a tangent screen examination. The patient fixatesa central target, and a stimulus is slowly moved from theperiphery towards the center of the screen along a particularmeridian until the patient reports detection of the stimulus.By repeating this procedure along different meridians, a con-tour of equal sensitivity—an isopter—can be plotted (Fig.2.13). The use of several different target sizes generates sev-eral different isopters and creates a map of visual field sensi-tivity. Scotomas, areas of low sensitivity or non-seeing areassurrounded by normal visual field regions, are also plotted.A well-performed kinetic tangent screen examination candetect subtle defects and provide quantitative informationfor the central visual field that is comparable to that obtainedby more sophisticated automated procedures.

Suprathreshold static visual field screening can also beaccomplished with the tangent screen. Using targets that arewhite on one side and black on the other, the wand can berotated to present and then extinguish the stimulus at keylocations throughout the visual field. The target size em-ployed is typically one that can be readily detected by per-


Figure 2.13. An example of an isopter generated by kinetic perimetrictesting. (From Johnson CA. Perimetry and visual field testing. In ZadnikK, ed. The Ocular Examination. Philadelphia, WB Saunders, 1996.)

sons with normal visual fields. In this manner, it is possibleto quickly determine whether or not visual field abnormali-ties are present.

The main advantages of the tangent screen are its flexibil-ity (i.e., variable distance from the patient, different colored

Figure 2.14. A demonstration of physiologically invalid tunnel vision(‘‘tubular vision’’) associated with nonorganic visual field loss, and thenormal cone-shaped expansion of the normal visual field as testing distanceis increased. (From Beck RW, Smith CH. The neuro-ophthalmologic exami-nation. Neurol Clin 1983;1�807–830.)

objects, single versus multiple stimuli used simultaneously),speed, and ease of use. Varying the distance of the patientfrom the screen can be helpful in differentiating organic fromnonorganic constriction of the visual field (Fig. 2.14). Themain disadvantages are the strong dependence of results onthe skill and technique of the perimetrist, the lack of stand-ardization, difficulty in monitoring the patient’s fixationwhile performing the visual field examination, and the needto establish age-related population norms.

Goldmann Manual Projection Perimeter

The Goldmann perimeter is a white hemispheric bowl ofuniform luminance (31.5 asb) onto which a small brightstimulus is projected. It is generally used to perform kineticperimetry, although static and suprathreshold static perime-try can also be tested with this perimeter. Unlike the Amslergrid and tangent screen, the Goldmann perimeter can be usedto evaluate the entire visual field. With one eye occluded,the patient fixates a small target in the center of the bowl,and the perimetrist monitors eye position by means of atelescope. A particular stimulus size and luminance isprojected onto the bowl, the target is moved from the farperiphery toward fixation at a constant rate of speed, typi-

Figure 2.15. Representation of kinetic perimetry results (below) com-pared with three-dimensional hill of vision (above). (From Johnson CA.Perimetry and visual field testing. In Zadnik K, ed. The Ocular Examination.Philadelphia, WB Saunders, 1996.)


cally 4–5� per second (161), and the patient is instructed topress a response button when he or she first detects the stimu-lus. The location of target detection is noted on a chart, andthe process is repeated for different meridians around thevisual field. Isopters and scotomas are plotted in a mannersimilar to that described for the tangent screen examination,except that both the target size and luminance can be ad-justed to vary stimulus detectability. This process producesa two-dimensional representation of the hill of vision thatis basically a topographical contour map of the eye’s sensi-tivity to light (Fig. 2.15). Kinetic testing (at least 1 or 2isopters) on the Goldmann perimeter can be performed incooperative children as young as 5 or 6 years of age.

Static Perimetry

Static perimetry uses a stationary target, the luminance ofwhich is adjusted to vary its visibility. Although it can beperformed manually using either the Goldmann or Tubinger

Figure 2.16. Visual field models for normaland glaucoma test results and their change dur-ing the perimetry test using SITA. As the testcontinues, the maximum likelihood model isupdated based on the results at the tested loca-tion and surrounding correlated locations. Inthis example, the glaucoma model graduallybecomes the most likely model at the end ofthe test.

perimeters, it is most often performed with an automatedperimeter such as the Humphrey Field Analyzer or the Octo-pus perimeter. Measurements of the increment threshold areobtained at a variety of visual field locations that are usuallyarranged in a grid pattern or along meridians. A bracket-ing or staircase procedure may be used to measure thresh-old sensitivity, although new techniques such as SITA(162–164) and ZEST (165–167) use Bayesian forecastingmethods.

The SITA method uses two maximum likelihood visualfield models: normal and glaucoma. The likelihood of a setof data is the probability of obtaining that set of data, giventhe chosen probability distribution model (in this case eithera normal or glaucoma model). The models are based on thefact that the slope of the frequency-of-seeing curves (vari-ability) increases with threshold. Figure 2.16 shows the twomodels. Log likelihood is on the y-axis and threshold (inten-sity) on the x-axis. At the beginning of the test, there is a


likelihood that the test location results are either normal orabnormal. As the test continues, the model is updated untilthe threshold is estimated with the given level of confidence.To reduce test time, the SITA-FAST algorithms interruptthe threshold even earlier. However, this reduction in testtime is at the expense of accuracy and variability.

Introduction of the SITA algorithm resulted in a 50% re-duction in test time. Thresholds are 1 to 2 db higher thanwith the use of the full staircase (full threshold) method. Theshortening of test time is likely the result of a combinationof less patient fatigue and interruption of the staircase proce-dure before threshold is reached. The algorithm has been sosuccessful in cutting down test time that full threshold testinghas largely been replaced. However, the efficacy of SITAfor serial examinations to detect change has not yet beenvalidated.

The presentation of visual field sensitivity for grid patternsis typically a gray scale representation (Fig. 2.17A), ratherthan the three-dimensional ‘‘hill of vision’’ that is producedduring kinetic perimetry. Areas of high sensitivity near thepeak of the hill of vision are denoted by lighter shadingand areas of low sensitivity by dark shading. Determinations

Figure 2.17. Representation of static perimetry results according to grayscale (A) and profile sensitivity plots (B).

along meridians are usually represented by a sensitivity pro-file plot (Fig. 2.17B).

The major advantages of automated static perimetry arestandardization of test conditions, quantitative visual fieldmeasurements, a normative database, statistical analysis pro-cedures, and automatic calibration. The major disadvantagesinclude a lengthy amount of time required for testing, limitedflexibility, the need for additional testing space, and a highvariability in areas of visual field damage.

Both static and kinetic perimetry are quantitative proce-dures that require a considerable amount of testing time.Suprathreshold static perimetry is a procedure that isfaster than quantitative techniques and is typically used forscreening purposes. There are a number of variations in testprocedures, strategies, and theoretical bases for suprathresh-old static perimetry (113,123,168). The basic technique,however, is that stimuli that can be easily detected by personswith normal peripheral vision are presented at specific loca-tions throughout the visual field. These locations are selectedto evaluate areas that are frequently affected by various ocu-lar or neurologic disorders that damage the visual pathways(e.g., glaucoma, chiasmal tumors). Locations at which thetarget is seen are denoted by one symbol and locations wherethe target is not seen are denoted by another.

Interpretation of Visual Field Information

A large amount of visual field information is derived fromperimetric testing, especially from automated perimetry.Test conditions and stimulus parameters used, indicators ofpatient reliability and cooperation, physiologic factors (pupilsize, refractive state, visual acuity, etc.), summary statisticsand visual field indices, and other items are presented inconjunction with sensitivity values for various locations inthe patient’s visual field. Visual field sensitivity can alsobe represented in many different forms (numerical values,deviations from normal, gray scale representations, probabil-ity plots, etc.). The following discussion presents a briefoverview of the various types of information provided onthe final printed outputs. Because of its current popularityand widespread use, this discussion and most of the exam-ples are derived from automated static perimetry. However,some examples of kinetic testing using the Goldmann perim-eter are presented for certain clinical cases, especially forsituations in which kinetic testing provides more informationabout visual field status.

There is no single type of data representation or item ofvisual field information that provides a sufficient or com-plete description of visual field properties. All of the avail-able information from the output needs to be evaluated inorder to properly interpret the results. Just as the results fromindividual components of a standard eye exam need to becombined to render an appropriate impression and diagnosis,consideration of all of the individual components of perime-try must be considered in order to properly appreciate thefindings.

Graphic Representation of Visual Field Data

In most instances, the numeric representation of visualfield information, whether by means of summary values such


as visual field indices or by sensitivity values for individualvisual field locations, is difficult to interpret. A graphic rep-resentation of visual field data makes it easier to evaluate,particularly for detecting specific patterns of visual field lossor for assessing progression or other visual field changesover time. There are three primary methods of graphicallyrepresenting visual field data: isopter/scotoma plots, profileplots, and gray scale plots (Fig. 2.18).

Ancillary

Several important pieces of information that should bechecked on each visual field examination are the positionof the eyelids, the refractive correction used for testing, pupilsize, and visual acuity. Ptosis can produce a superior visualfield defect that may be minimal or significant (Fig. 2.19A).High refractive corrections (greater than 6-diopter sphericalequivalent) can sometimes produce trial lens rim artifacts(Fig. 2.19B). When a patient’s spherical equivalent correc-tion for perimetric testing exceeds 6 diopters, it is advisable

Figure 2.18. A comparison of the various graphic methods of representing visual field data: profile plot (A); gray scale plot(B); isopter/scotoma plot (C).

to use a soft contact lens correction that is appropriate forthe testing distance to avoid lens rim artifacts. Proper nearrefractive corrections that are appropriate for the near testingdistance of the perimeter bowl and the patient’s age mustbe used to minimize the likelihood of refraction scotomasand sensitivity reductions from blur (Fig. 2.19C). Small pu-pils (less than 2 mm diameter) can produce spurious testresults, especially in older persons who may have early len-ticular changes. If pupil size is small, the patient should bedilated to 3 mm or greater (Fig. 2.19D). Finally, the patient’svisual acuity can also provide useful information when as-sessing generalized visual field sensitivity loss and the po-tential sources responsible for the loss.

Reliability Indices

The quality of information obtained from perimetry andvisual field testing depends on a patient’s cooperation, will-ingness, and ability to respond in a reliable fashion and main-tain a consistent response criterion. It is important to have


Figure 2.19. Influences on visual field test results. A, An example of visual field results for ptosis before (left) and after(right) taping up the upper lid and brow. B, Example of trial lens rim artifact (left) and its disappearance (right) after realigningthe patient. C, Refractive error introduced by improper lens correction (left) and results after proper lens was employed (right).D, Visual field results obtained in the same eye with a 1 mm (left) and a 3 mm (right) pupil diameter.


an assessment of patient reliability and consistency in orderto properly evaluate the significance of visual field informa-tion. With manual perimetry, it is possible to monitor thepatient’s fixation behavior directly by means of a telescopicviewer. The use of ‘‘catch’’ trials has been as an index ofpatient response reliability. False-positive errors (responseswhen no stimulus is presented) and false-negative errors(failure to respond to a stimulus presented in a region previ-ously determined to be able to detect equal or less detectabletargets) can be monitored throughout the test procedure.

Automated test procedures not only have the capabilityof monitoring false-positive errors, false-negative errors, andfixation behavior in the same manner as described above,but also can obtain an assessment of response fluctuation byretesting a sample of visual field locations. Also, indirectindicators of fixation accuracy (e.g., whether or not a patientresponds to a target presented to the physiologic blind spot)can be monitored. An additional advantage of automated testprocedures is that these reliability indices (false positives,false negatives, fixation losses, short-term fluctuations) canbe immediately compared with those of age-adjusted normalcontrol subjects, thereby providing an indication as towhether or not the patient’s reliability parameters are withinnormal population characteristics.

Some of the reliability indices for automated perimetryare not always accurate indicators of a patient’s true perfor-mance. For example, false-negative rates are correlated withvisual field deficits, i.e., there is an increase in false-negativeresponses with increased field loss (144). Thus, high false-negative rates may be more indicative of disease severitythan of unreliable patient responses. Excessive fixationlosses can be caused by factors such as mislocalization ofthe blind spot during the initial phases of testing, misalign-ment or head tilt of the patient midway through testing, orinattention on the part of the technician administering thevisual field examination. Also, one should be careful not toconsider reliability indices as a replacement for technicianinteraction and monitoring of patients. Some patients areuncomfortable when left alone in a darkened room duringautomated perimetry testing. In addition, misalignment ofthe patient, drowsiness, and related factors can occur duringtesting and go undetected if the patient is not adequatelymonitored. It is important to remember that it is the testprocedure that is automated, not the patient.

Although reliability indices are helpful in determining ifthe visual field is accurate, they are not sufficient to eliminatethe possibility that a visual field defect is nonorganic in na-ture. It has been shown that both patients and otherwisenormal subjects can ‘‘fool’’ the automated perimeter, pro-ducing a variety of abnormal fields despite maintaining relia-bility indices that are within normal limits (169–171).

Visual Field Indices

A distinct advantage afforded by automated perimeters isthe ability to provide summary statistics, usually called vis-ual field indices. The Mean Deviation (MD) on the Hum-phrey Field Analyzer and the Mean Defect (MD) on the

Octopus perimeters refer to the average deviation of sensitiv-ity at each test location from age-adjusted normal populationvalues. They provide an indication of the degree of general-ized or widespread loss in the visual field. The Pattern Stan-dard Deviation (PSD) on the Humphrey Field Analyzer andthe Loss Variance (LV) on the Octopus perimeter present asummary measure of the average deviation of individual vis-ual field sensitivity values from the normal slope after cor-recting for any overall sensitivity differences, i.e., MD. Theyrepresent the degree of irregularity of visual field sensitivityabout the normal slope and therefore indicate the amount oflocalized visual field loss, because scotomas produce signifi-cant departures from the normal slope of the visual field.Corrected Pattern Standard Deviation (CPSD) and CorrectedLoss Variance (CLV) take into account the patient’s short-term fluctuation (STF) during testing. STF is derived bytesting a sample of ten locations twice to determine the aver-age deviation of repeated measures. This correction mini-mizes the influence of patient variability on the local devia-tion measures. Note that CPSD and STF are not evaluatedby the SITA test algorithm.

Probability Plots

Another advantage of automated static perimetry is that apatient’s test results are compared with age-adjusted normalpopulation values. Thus, it is possible to determine theamount of deviation from normal population sensitivity val-ues on a point by point basis for all visual field locationstested. A useful means of expressing this information is bymeans of probability plots. The Humphrey Field Analyzerhas two methods of presenting this type of information. Oneis called the ‘‘Total Deviation Plot’’ and the other is calledthe ‘‘Pattern Deviation Plot.’’ For the Total Deviation Plot,each visual field location has one of a group of differentsymbols indicating whether the sensitivity is within normallimits, or is below the 5, 2, 1, or 0.5% of normal limits,respectively. In other words, visual field locations or in-dices that have a probability corresponding to p less than1% mean that this value is observed less than 1% of thetime in a normal population of the same age. This providesan immediate graphic representation of the locations thatare abnormal and the degree to which they vary fromnormal levels.

The Pattern Deviation Plot is similar to the Total Devia-tion Plot, except that the determinations are performed afterthe average or overall sensitivity loss has been subtracted,thereby revealing specific locations with localized devia-tions from normal sensitivity values. The value of these rep-resentations is twofold. First, they provide an immediate in-dication of the locations with sensitivity loss. Second, thecomparison of the Total and Pattern Deviation Plots providesa clear indication of the degree to which the loss is diffuse orlocalized. If the loss is predominantly diffuse, the abnormallocations will appear on the Total Deviation Plot, but all ormost of these locations will be within normal limits on thePattern Deviation Plot (Fig. 2.20A. If the deficit is predomi-nantly localized, the Total and Pattern Deviation Plots will


Figure 2.20. Examples of diffuse loss (A), localized loss (B), and ‘‘triggerhappy’’ (C) patient results as they are depicted on the Total Deviation andPattern Deviation probability plots for the Humphrey Field Analyzer.

look almost identical (Fig. 2.20B). The degree of similaritybetween the Total and Pattern Deviation Plots thus gives anindication of the proportion of loss that is diffuse and local-ized. In a few instances, the Total Deviation Plot may appearto be normal, but the Pattern Deviation Plot reveals a numberof abnormal locations (Figs. 2.20C and 2.21). This occurswhen the patient’s measured sensitivity is significantly betterthan normal, and it is most often caused by a patient whopresses the response button too often (‘‘trigger happy’’).

Progression of Visual Field Loss

The determination of whether a patient’s visual field im-proves, worsens, or remains stable over time is the mostdifficult aspect of visual field interpretation. Although thereare several quantitative analysis procedures available forevaluating visual field progression, none of them enjoys

complete acceptance by the clinical ophthalmic community(172). Nevertheless, the use of quantitative statistical analy-sis procedures may be helpful in monitoring a patient’s vi-sual field status.

There are several important factors to consider when eval-uating a patient’s visual field status over time. First, it isnecessary to examine the test conditions that were presentfor each visual field examination. If different test strategies,target sizes or other test conditions are different from oneexamination to another, it is difficult to compare the results,because the type of test procedure and the stimulus size (andcharacteristics) can significantly alter the appearance of thevisual field (Figs. 2.22 and 2.23). Second, it is important todetermine if there are any differences in patient conditionsfrom one visual field to another. If there are meaningfuldifferences in pupil size, refractive corrections, visual acuity,time of day, or other factors (e.g., upper lid taped on oneoccasion and not on another occasion), this can have a dra-matic effect on the visual field results obtained on differentvisits (Fig. 2.19). Third, unless the visual field changes aredramatic, it is important to base judgments of visual fieldprogression or stability on the basis of the entire series ofvisual fields that are available. It is not possible to distinguishsubtle visual field changes from long-term variation on thebasis of two visual fields (e.g., comparing the current visualfield to the previous visual field). In particular, patients withmoderate to advanced visual field loss can sometimes exhibitconsiderable variations from one visual field to another.Also, factors such as fatigue and experience can pro-duce significant differences in visual field characteristics(147–154). If it is suspected that a change in visual fieldloss has occurred, it is best to repeat the examination on aseparate visit to confirm the suspected change. Dependingon which part of the sequence and which eye is examined,any two successive visual fields can reflect apparent im-provement, progression, or stability of the visual field.

Five-Step Approach to Visual Field Interpretation

One of the common errors that occur in visual field inter-pretation is the lack of attention to details and specific pat-terns of visual field loss before obtaining a global evaluationof the visual field. To avoid this tendency, we suggest asimple five-step approach to visual field interpretation:

1. Determine if the visual field is normal or abnormal foreach eye separately. Automated perimetry results provideassistance with this task, because they show both point-by-point and summary comparisons of the patient’s testresults with age-matched normal population values. Ifboth eyes are normal, both in terms of statistical compari-son and clinical assessment, then further evaluation is notnecessary. However, subtle visual field loss can some-times be present despite visual field indices that arewithin normal limits. Perhaps the most common of theseoccurrences are the subtle vertical steps in the superiorvisual field that may reflect an early bitemporal chiasmallesion.


Figure 2.21. An example of automated static perimetry results from a ‘‘trigger happy’’ patient who presses the responsebutton too often and inappropriately.

Figure 2.22. Examples of different fields obtained when pa-tients with a field defect are tested with different strategieson an automated perimeter or with different perimeters. A, Apatient with an optic neuropathy who was tested on two differ-ent automated perimeters. Note marked difference in results.(Figure continues.)

Figure 2.22. Continued. B, A macular scotoma using acentral 30� test (left) and central 10� test (right). Note appear-ance of scotoma when 10� test is performed. C, Advancedglaucoma using a central 30� test (left) and a central 10� test(right).

Figure 2.23. Appearance of visual fields ob-tained by different techniques in a patient withretinitis pigmentosa. A, Visual field defects withstatic perimetry using a Humphrey 30-2 test witha size III target for the left and right eyes showsdiffuse reduction in sensitivity in each eye witha small area of central sparing. B, Results usinga size V target for the central 30�. Note expansionof the clear central area. C, Results obtained byfull field kinetic perimetry using a Goldmann pe-rimeter. Note that with static perimetry the trueextent of the field defects cannot be appreciated.With kinetic perimetry the scotomatous nature ofthe defects can be appreciated.

108


2. If one or both visual fields are abnormal, examine theancillary information to determine if proper test condi-tions were employed, the appropriate near correction wasused (based on the patients’ age, distance refraction, andwhether or not they were cyclopleged), and the pupil sizewas sufficiently large. Also, check for patterns of visualfield loss that are indicative of a trial lens rim artifact, adroopy upper eyelid, or other nonpathologic conditionsthat may account for the visual field loss. Fatigue, drowsi-ness, and related conditions can also produce apparentvisual field loss. It is crucial that the person who performsthe perimetric testing, especially with automated perime-tric tests, be attentive to these factors. A surprising num-ber of visual field deficits can be attributed to nonpatho-logic influences.

3. Determine if the visual field is abnormal in both eyes or

Figure 2.24. Monocular field loss in a patient with myelinated nervefibers in the right eye. Kinetic visual field testing, performed on the Tub-inger perimeter (top), shows an inferior arcuate scotoma that correspondsto the area of myelinated nerve fibers in the superior arcuate region (bottom).

Figure 2.25. Humphrey visual field (top) and corresponding fundus photo(bottom) from a patient with low tension glaucoma in the right eye. Notemoderate cupping (large arrow), small peripapillary nerve fiber layer hem-orrhage (medium arrow), and wedge-shape nerve fiber layer defect (thinarrows) that corresponds to the superior arcuate field defect detected byperimetry.

in only one eye. If the visual field is abnormal in onlyone eye, the defect is almost always caused by a disorderanterior to the optic chiasm (Figs. 2.24–2.27). If the vi-sual field of both eyes is abnormal, it means that the defi-cit is at or posterior to the optic chiasm (Figs. 2.28–2.30)or that the patient has bilateral intraocular or optic nervedisease (Figs. 2.31–2.33).

4. Determine the general location of the visual field lossfor each eye independently. Specifically, determine if thevisual field loss is in the superior or inferior hemifield,the nasal or temporal hemifield, or the central portion ofthe field. This is especially important for the nasal andtemporal hemifield assessment. If the loss is extensive,determine where the greatest amount of visual field lossis present. If the visual field loss is bitemporal and re-spects the vertical midline, then a chiasmal locus should


Figure 2.26. Unilateral visual field defect in the left eye of a patient with a peripapillary staphyloma. Top, Visual field ofthe left eye shows marked enlargement of the physiologic blind spot. Bottom left, Appearance of left ocular fundus. Bottomright, Axial computed tomographic scan shows ovoid enlargement of posterior aspect of the left globe (arrow). The patient’svisual acuity in this eye was 20/20.


Figure 2.27. Unilateral visual field defect in a patient with segmental hypoplasia of the right optic nerve. Visual acuity was20/20 in the eye. Left, Kinetic perimetry using a Goldmann perimeter shows marked inferior altitudinal defect that does notobey the horizontal midline. Note preservation of the central field to small isopters. Right, Fundus photograph shows absenceof the upper part of the disc substance. The thin arrow indicates the location of the optic disc and the thick arrow indicatesthe scleral crescent.

Figure 2.28. Bilateral visual field defect in apatient with a tumor in the region of the opticchiasm. Top, Static perimetry reveals a bilateraltemporal hemianopia, worse in the right eye(right). Bottom, Sagittal (left) and coronal(right) T1-weighted magnetic resonance im-ages show a large mass in the sella turcica withsuprasellar extension (large arrows). The masscompresses and elevates the optic chiasm(small arrows).


Figure 2.29. Preoperative and postoperative visual fields in a patient with a craniopharyngioma. A and B, Kinetic perimetryreveals an incomplete incongruous left homonymous hemianopia. C, Axial computed tomographic scan shows an enhancinglesion in the suprasellar region. D and E, Marked improvement in visual fields following removal of the tumor. The homonymousfield defect resulted from compression of the right optic tract by the mass.


Figure 2.30. Bilateral visual field defects in a patient with an occipital lobe infarct. Top, Static perimetry using a Humphreyvisual field analyzer shows a left homonymous field defect with macular sparing. Middle, T2-weighted axial magnetic resonanceimage shows a hyperintense region consistent with an infarct (medium arrow) in the right occipital lobe. Note normal appearanceof the posterior aspect of the right occipital lobe (thick arrow), corresponding to the macular sparing. In addition, the deepportion of the calcarine fissure (thin arrow), which has only monocular representation and is responsible for the temporalcrescent, also appears normal. Bottom, Kinetic perimetry confirms a left homonymous hemianopia with macular sparing andsparing of the temporal crescent of the visual field of the left eye.


Figure 2.31. Bilateral visual field defects in a patient with a progressive retinal cone dystrophy. Top, Static perimetry showsdense central field defects with extension toward the periphery. Bottom, Kinetic perimetry demonstrates dense central scotomaswith sparing of the peripheral visual field of both eyes.

Figure 2.32. Bilateral visual field defects in a patient with pseudotumor cerebri. Kinetic perimetry demonstrates completeloss of the nasal visual field of both eyes, with involvement of the temporal fields as well. (Figure continues.)


Figure 2.32. Continued. Fundus pho-tographs show bilateral chronic papil-ledema with early atrophy.

Figure 2.33. Bilateral visual field defects in a patient with bilateral optic disc drusen. A and B, Static perimetry revealssignificant nasal field loss in both eyes. C, Axial computed tomographic scan set at bone window density shows calcifieddrusen. D and E, Fundus photographs show extensive optic disc drusen. Note absence of visible nerve fiber layer and constrictionof retinal arteries.


be strongly suspected, especially if the deficit is in thesuperior temporal quadrant in each eye (Fig. 2.34). If thevisual field loss is nasal in one eye and temporal in theother eye (i.e., homonymous), then a retrochiasmal loca-tion should be suspected (Fig. 2.35). Binasal defects ora nasal deficit in only one eye should generate a suspicionof glaucoma, various nonglaucomatous optic neuropa-thies, or certain types of retinal disorders (Figs. 2.36 and2.37). A central deficit in one or both eyes may indicatea macular disorder (especially if the visual field defectdoes not connect to the blind spot) or an optic neuropathy(Figs. 2.38 and 2.39). With this simple step, a global viewof visual field properties is generated, and a hierarchy ofpotential locations of damage along the visual pathwayand probable disease entities is hypothesized.

Figure 2.34. Mild superior bitemporal field defect in a patient with 20/20 vision in both eyes. The gray scale representationdemonstrates the superior temporal deficit respecting the vertical meridian in both eyes, although the probability plots do notshow the deficit in the right eye. The patient was found to have a pituitary adenoma.

5. Look at the specific shapes, patterns, and features of thevisual field loss (Figs. 2.40–2.43 and Table 2.4). Does thedefect respect either the horizontal or vertical meridians?What is the shape of the deficit (arcuate, oval, circular,pie-shaped, irregular)? Does the deficit ‘‘point’’ to theblind spot or to fixation? If there is visual field loss inboth eyes, is it congruous or incongruous, symmetric be-tween the two eyes, or asymmetric? Do the edges of thedefect have a steep or a gradual sloping profile? Theseand other specific features of the visual field should pro-vide confirmatory information for the location of thedamage determined by Step 4 or allow one to differentiateamong several possible alternative locations. However,it should not be used as the initial basis for generating ahypothesis about location of damage. Attention to


Figure 2.35. Left homonymous hemianopia with macular sparing in a patient with a right occipital lobe infarct. Top, Staticperimetry demonstrates a dense left homonymous hemianopia with about 5� of inferior macular sparing. Note marked congruityof the field defects in the two eyes. Bottom, Kinetic perimetry reveals that the homonymous field defect has both absolute andrelative features. The congruous nature of the defects is apparent, at least with small isopters. Middle, Axial T1-weightedmagnetic resonance shows hyperintensity in right occipital lobe, consistent with the congruous homonymous visual field defect.


Figure 2.36. Bilateral visual field defects in a patient with bilateral optic nerve pits and focal loss of the nerve fiber layer.A, Kinetic perimetry in left eye shows small superior arcuate defect encroaching on fixation. B, Kinetic perimetry in right eyeshows large superior nasal/arcuate defect. C, Fundus photograph of left eye shows a small inferotemporal optic pit (largearrow) and loss of nerve fiber layer in the inferior arcuate region (small arrows). D, Fundus photograph of the right eye showsan inferior pit (large arrow) associated with a broad region of nerve fiber loss in the inferior and inferotemporal region (smallarrows).

A B

Figure 2.37. Bilateral visual field defects in a patient with postpapilledema optic atrophy. A and B, Kinetic perimetry showsmild loss of the nasal visual field in the left (A) and right (B) eyes. Note that most of the field loss is relative. (Figure continues.)


C D

Figure 2.37. Continued. C and D, Fundus photographs show moderate postpapilledema optic atrophy.

Figure 2.38. Bilateral visual field de-fects in a patient with bilateral central se-rous chorioretinopathy. A and B, Kineticperimetry reveals bilateral central defectswith normal peripheral fields. C and D,Early (C) and late (D) fluorescein angiog-raphy shows leakage of dye consistentwith central serous chorioretinopathy inthe posterior pole of the left eye (arrows).

Figure 2.39. Improvement in a visual field defect as detected by static perimetry in a patient with optic neuritis over a 15-day period. Note marked clearing of the defect. (From Keltner JL, Johnson CA, Spurr JO, et al. Visual field profile of opticneuritis: One year followup in the Optic Neuritis Treatment Trial. Arch Ophthalmol 1994;112�946–953.)


Figure 2.40. Visual field defects indicating an anterior chiasmal mass in a 7-year-old child with decreased vision in the lefteye. A, Kinetic perimetry in the left eye reveals a dense central scotoma with constriction of the peripheral field. B, Kineticperimetry in the right eye reveals a supertemporal field defect (junctional scotoma of Traquair). C, Axial computed tomographicscan shows a large circular lesion in the suprasellar region (arrows). At surgery, a craniopharyngioma was found and removed.D, After surgery, kinetic perimetry shows substantial improvement in the visual field of the left eye. E, Kinetic perimetry inthe right eye reveals a normal visual field.


Figure 2.41. Two examples of visual field deficits produced by lesions of the lateral geniculate body (LGB). Top, Kineticperimetry from a patient who experienced a stroke reveal a left quadruple sectoranopia from damage to the LGB in the territoryof the distal anterior choroidal artery. Bottom, Right homonymous horizontal sectoranopia with metastatic cancer to the LGBin the region supplied by the lateral choroidal artery. (Courtesy of Dr. William T. Shults.)

specific features of the visual field before getting a globalview of the visual field from Step 4 may lead to misinter-pretation of visual field information.

The approach to visual field interpretation outlined aboveis not intended to cover all possible scenarios but is rathermeant as a guide to identify most kinds of visual field deficitsand to avoid many of the common pitfalls. Once the patternand degree of visual field loss has been established, a differ-ential diagnosis needs to be determined. If there is doubtabout the validity of visual field results, the test should berepeated when the patient is well-rested. Pathologic visualfield changes usually are replicable, whereas nonpathologicvisual field changes typically are not. If there is concernabout fatigue affecting visual field results, a shorter test pro-cedure should be employed.

New Perimetry Tests

Automated perimetry has enhanced the clinical utility ofvisual field testing by providing standardized procedures,quantitative measures, normative population characteristics,immediate statistical analyses, new graphic representationsof data, and many other desirable features. However, thebasic test procedures have essentially remained the samefor more than 150 years. Usually, a small white stimulus ispresented on a uniformly illuminated adapting background,and the detection threshold of the stimulus is determined atvarious locations throughout the visual field.

In order to improve sensitivity of visual field testing, sev-eral test procedures have been modified for use in perimetry.Although the tests vary widely in terms of the visual func-tions that they measure, they have a common objective: bycreating a unique stimulus display, these tests attempt to


Figure 2.42. Visual field defects caused by postgeniculate lesions in thetemporal (top), parietal (middle), and occipital (bottom) lobes as definedby static perimetry. Top, Right incomplete incongruous homonymous hemi-anopia, denser above, from left temporal lobe lesion. Middle, Left incom-plete incongruous homonymous hemianopia, denser below, from lesion ofthe right parietal lobe. Top, Right congruous superior quadrantanopia fromlesion of the inferior aspect of the left occipital lobe.

isolate (or strongly bias) threshold responses to be mediatedby a specific subpopulation of neural mechanisms, insteadof the wide range of neural mechanisms stimulated by con-ventional perimetry.

These test procedures have several theoretical advantages.First, because these tests are designed to target specific vis-ual mechanisms, their response properties bear a strong link-age to the underlying physiology and anatomy of the visualpathways. Second, if certain diseases cause selectivelygreater amounts of damage to some visual mechanisms thanothers, these new test procedures may be able to detect earlylosses or changes in visual function that may not otherwisebe noticed with conventional perimetry. Finally, because

Table 2.4Differential Diagnosis of Visual Field Deficits

I. GENERAL DEPRESSIONA. Cataract (diffuse depression from cataracts may improve with

dilation)B. Corneal disease (shows no improvement with dilation)C. Other media opacitiesD. Some optic neuropathies

II. ENLARGED BLIND SPOTA. Optic nerve disease

1. Papilledema and big blind spot syndrome2. Drusen of the optic nerve head3. Congenital optic nerve lesion (coloboma, staphyloma)4. Optic neuritis

B. Retinal disease1. Multiple evanescent white dot syndrome (MEWDS)2. Acute zonal occult outer retinopathy (AZOOR)

C. High myopiaIII. ARCUATE, ALTITUDINAL, NASAL STEP, NASAL DEPRESSION

A. Optic nerve disease1. Glaucoma2. Papilledema3. Drusen of the optic nerve head4. Other optic neuropathies (AION, optic neuritis, etc.)

B. Branch artery occlusionIV. CROSSES THE VERTICAL AND HORIZONTAL MERIDIANS

A. Retinal disease1. Ring scotomas, peripheral depression, “scalloped” field loss

B. Optic neuropathy1. Generalized depression, sparing of central vision

C. Fatigue, poor testing ability1. Fatigue in conjunction with visual pathology

D. Malingering1. Peripheral depression, square visual fields, spiraling or crossed

isopters, inconsistent patterns of lossV. CENTRAL OR CENTROCECAL DEFECTS

A. Maculopathy (visual acuity often more affected than visual field)B. Optic neuropathies of all types

VI. BITEMPORAL DEFECTSA. Superior bitemporal defects (pituitary adenoma)B. Inferior bitemporal defects (craniopharyngioma, hypothalamic

tumor)VII. HOMONYMOUS HEMIANOPSIA

A. Complete homonymous hemianopsia1. Retrochiasmal defect with no further localizing value

B. Tongue- or keyhole-shaped homonymous defect, or remainingvisual field1. Lateral geniculate lesion

C. Incongruous homonymous hemianopsia (anterior optic tract,radiations)1. Optic tract2. Temporal lobe (“pie in the sky” defect)3. Parietal lobe (“pie on the floor” defect)

D. Highly congruous homonymous hemianopsia1. Occipital lobe lesion

a. “Cookie cutter” punched-out lesionb. Macular sparingc. Temperal crescentd. Statokinetic dissociation


L R

Figure 2.43. Complete homonymous hemianopia with macular sparing from an occipital lobe lesion. A and B, Kineticperimetry shows a complete left homonymous hemianopia with about 5� of macular sparing. C, Axial computed tomographicscan shows a small low-density area, consistent with an infarct, in the right occipital lobe (arrow), with sparing of the occipitaltip.

these test procedures are designed to isolate specific subpop-ulations of neural mechanisms, they eliminate much of theredundancy and overlap that is normally present in the visualpathways. By reducing this redundancy, it becomes easierto detect early, subtle losses or changes in visual function,even if these losses are not selective (173).

In this section, we briefly describe five perimetry teststhat appear to have the greatest potential for clinical utilityin neuro-ophthalmologic diagnosis: Short Wavelength Auto-mated Perimetry [SWAP], High-Pass Resolution Perimetry(HRP), Flicker Perimetry, Motion and Displacement Perim-etry, and Frequency Doubling Perimetry.

Short Wavelength Automated Perimetry (SWAP)

Short Wavelength Automated Perimetry [SWAP] utilizesa bright yellow background and a large short-wavelength

(‘‘blue’’) stimulus to isolate and measure the sensitivity ofshort-wavelength chromatic mechanisms. The bright yellowbackground depresses the sensitivity of middle (‘‘green’’)and long (‘‘red’’) wavelength mechanisms, thereby allowingthe sensitivity of the short-wavelength system to be mea-sured using a large blue target. The test is available on sev-eral automated projection perimeters and can utilize the sametest strategies, target presentation patterns, and other param-eters that are employed in conventional automated perimetry(174–177). The test procedure is commercially available forthe Humphrey Field Analyzer, which provides a statisticalanalysis procedure and age-related normative database forinterpreting results. The SITA strategy is also available forSWAP (178).

A number of longitudinal and cross-sectional investiga-tions have established that SWAP is not only an early indica-


tor of damage from glaucoma but that it also detects visualfield defects that are not determined by conventional auto-mated perimetry (174–177). About 5–20% of glaucoma sus-pects with normal visual fields when tested by conventionalautomated perimetry have localized deficits when testingwith SWAP. In addition, SWAP deficits are present in35–40% of high-risk glaucoma suspects compared withabout 8% of low-risk glaucoma suspects. Longitudinal in-vestigations demonstrate that SWAP is able to predict theonset and location of subsequent glaucomatous visual fieldloss by conventional perimetry 3–5 years before its occur-rence. SWAP is also able to predict subsequent progressionof glaucomatous visual field loss (Fig. 2.44). However, itshigh variability limits its ability to detect progression (176).

SWAP is also useful for patients with neuro-ophthalmo-logic disorders. Keltner and Johnson (179) studied 40 pa-tients with various neuro-ophthalmologic disorders. In someinstances, SWAP deficits were present in eyes with normalvisual fields obtained with conventional automated perime-

Figure 2.44. Results of a 5-year longitudinal comparison of standardwhite-on-white perimetry (left) and short wavelength automated perimetry[SWAP] (right) in an ocular hypertensive patient who converted to glau-coma. Note that the SWAP deficit was present before the standard visualfield loss, and predicted its development and location several years later.(From Johnson CA, Adams AJ, Casson EJ, et al. Blue-on-yellow perimetrycan predict the development of glaucomatous visual field loss. Arch Oph-thalmol 1993;111�645–650.)

try. In cases in which visual field loss was evident for con-ventional automated perimetry, the SWAP deficit was moreextensive (Figs. 2.45 and 2.46).

High-Pass Resolution Perimetry (HRP)

High-pass resolution perimetry (HRP) was developed byFrisen (180,181) and consists of a series of ‘‘ring’’ targetsof varying size that are generated on a video monitor byperforming a ‘‘high pass’’ spatial frequency filtering of atarget incorporating a light circular center and a dark annularsurround (Fig. 2.47). The average luminance of the ring stim-ulus is equal to the background. This combination createsa vanishing optotype. The special property of a vanishingoptotype is that detection and resolution occur at approxi-mately the same threshold. The ring test is believed to pre-dominantly test the function of parvocellular mechanismsthat are responsible for the processing of fine detail, formvision, and related spatial vision functions (181).

Sample et al. (182) reported a 67% agreement betweenHRP and the Humphrey Field Analyzer in a group of normalpersons, ocular hypertensives, and patients with primaryopen-angle glaucoma. In patients with visual field defectsdetected with both tests, there was a 92% agreement in thelocation of the deficit. Lachenmayr et al. (183,184) reportedthat HRP was significantly less sensitive in detecting earlyglaucomatous visual field loss than either conventional auto-mated perimetry or flicker perimetry (see later).

Evaluations of HRP in patients with neuro-ophthalmo-logic disorders are encouraging (180–182,185–192). For ex-ample, Wall et al. (188) found that in patients with pseudotu-mor cerebri, HRP had slightly lower sensitivity and slightlyhigher specificity than automated perimetric testing using aHumphrey Field Analyzer, although the differences were notstatistically significant. Wall (187) also reported that HRPwas useful for evaluating patients with optic neuritis andwas especially sensitive in revealing subtle deficits in thefellow ‘‘uninvolved’’ eyes of optic neuritis patients.

Most importantly, the ring test has been shown to have lowretest variability (188,193). Chauhan and coworkers haveshown that the ring test can detect visual field progression inglaucoma significantly earlier than conventional automatedperimetry.

The main advantages of HRP are its relatively quick ex-amination time, the interactive feedback the test procedureprovides to patients, excellent patient ergonomics, low retestvariability, and the high degree of patient preference for HRPover conventional perimetric techniques. The main disad-vantages are its greater susceptibility to blur, and alignmentproblems (e.g., lens rim artifacts).

Flicker Perimetry

Another psychophysical procedure that shows promisinginitial results for detecting and evaluating subtle visual lossis the detection of flicker. The rationale underlying flickerperimetry testing is that high temporal frequencies of flickerpreferentially stimulate ganglion cells that project to themagnocellular layers of the lateral geniculate body. M-cell


Figure 2.45. Gray scale and total deviation plots for standard automated perimetry (top) and short wavelength automatedperimetry [SWAP] (bottom) for an asymptomatic patient with multiple white matter abnormalities on magnetic resonanceimaging (thick and thin arrows). The standard visual fields are normal, whereas SWAP reveals a right homonymous hemianopia,probably related to the white matter lesions in the left occipital lobe (large arrow). (From Keltner JL, Johnson CA. Shortwavelength automated perimetry [SWAP] in neuro-ophthalmologic disorders. Arch Ophthalmol 1995;113�475–481.)

fibers primarily consist of large-diameter ganglion cell axonsthat may be preferentially damaged in glaucoma. Thus, bypresenting a stimulus that preferentially stimulates this groupof nerve fibers, mild glaucomatous deficits may be morereadily detected. Flicker perimetry is effective in detectingmild glaucomatous visual field loss. Indeed, in some ocularhypertensives, flicker deficits are found in locations withinthe visual field in which there were normal responses whentested using conventional automated perimetry. In addition,this form of perimetry seems to have predictive value in

distinguishing which ocular hypertensives with normal vis-ual fields will develop glaucomatous visual field loss withinseveral years (194). Thus, flicker perimetry seems to be auseful adjunct to conventional automated perimetry, espe-cially for detecting early glaucomatous losses.

Flicker sensitivity has several desirable features as a clini-cal diagnostic test procedure. Unlike many psychophysicaltests, flicker detection thresholds are relatively unaffectedby moderate amounts of blur, light scatter, and other formsof image degradation (195). Thus, optical factors such as


Figure 2.46. Pretreatment (top) and posttreatment (bottom) standard visual fields (left) and Short Wavelength AutomatedPerimetry [SWAP] fields (right) in a patient with a right optic nerve sheath meningioma. Standard perimetry shows a minimalinferonasal defect in the visual field of the right eye (top left), whereas SWAP shows an extensive reduction in sensitivity (topright). Middle, T1-weighted axial MR image after intravenous injection of paramagnetic contrast material shows enlargementand enhancement of the posterior portion of the right optic nerve (arrow). Following radiation treatment, standard automatedperimetry is normal (bottom left), but SWAP shows a persistent nasal step (bottom right). (From Keltner JL, Johnson CA.Short wavelength automated perimetry [SWAP] in neuro-ophthalmologic disorders. Arch Ophthalmol 1995;113�475–481.)

cataract, refractive error, and media opacities do not influ-ence flicker sensitivity as much as they affect visual acuityand related psychophysical tests. The primary disadvantageof flicker sensitivity is that specialized equipment must beused. Most automated projection perimeters and other clini-cal instruments are not easily modified to perform this typeof visual field testing.

Motion Perimetry

The ability to detect motion or small displacements of astimulus at various locations in the visual field can be

adapted for use as a perimetric test procedure. As with hightemporal frequency flicker, the rationale underlying this testprocedure is that motion is preferentially detected by M-cellmechanisms, which may be more susceptible to glaucoma-tous damage. Thresholds for detection of motion may there-fore reveal early glaucomatous defects in localized visualfield locations.

Two different approaches have been used to evaluate mo-tion sensitivity of the visual field. The first method measuresthe minimum displacement of a small target superimposedon a uniform background that can be detected as movement


Figure 2.47. High-pass resolution perimetry targets. (From Frisen L. Highpass resolution perimetry: Recent developments. In Heijl A, ed. PerimetryUpdate 1988/1989. Amsterdam, Kugler and Ghedini, 1989�383–392.)

(196–199). Motion displacement thresholds are then deter-mined for a number of visual field locations in a mannersimilar to traditional static perimetry. In this way, motionsensitivity can be determined for small localized regions ofthe visual field. The second method presents a large displayof small dots that are moving in random directions (Brown-ian-like motion). A stimulus is produced by briefly movinga small group of dots in the same direction (coherence).The patient’s task is to detect this coherent direction of dotmotion. A ‘‘motion coherence’’ threshold is determined byvarying the percentage of dots within the small group thatare moving in the same direction (200,201), or by keepingcoherence constant and changing the size of the patch ofcoherent motion (202–204) (Fig. 2.48). This test evaluateslarge visual field regions but requires the combined inputfrom a population of cells to be able to detect motion. Otherversions of this test limit the size of the stimulus so thatmore localized regions of the visual field can be tested(202,203,205).

Studies of motion and displacement threshold perimetryindicate that motion sensitivity is abnormal in glaucoma pa-tients, and that motion thresholds are sometimes able to de-tect subtle glaucomatous losses that are not evident withconventional automated perimetry (196–199,202,204,206).

Figure 2.48. An example of the video stimuli used to determine motionand coherence thresholds for motion perimetry. (From Wall M, Ketoff KM.Random dot motion perimetry in patients with glaucoma and in normalsubjects. Am J Ophthalmol 1995;120�587–596.)

Longitudinal studies are needed to verify the clinical signifi-cance of these findings and those of Wall and Montgomery(203) that motion perimetry is able to detect localized visualfield defects in patients with idiopathic intracranial hyperten-sion (see Chapter 5).

Motion and displacement perimetry have several desirablecharacteristics as clinical diagnostic test procedures. Motiondetection is a very robust visual function, being only mod-estly affected by such factors as contrast, luminance, adapta-tion level, and target size (207). In addition, motion detec-tion, like flicker sensitivity, is very resistant to the effectsof cataract, refractive error, and other forms of image degra-dation (199). The dynamic stimulus range for motion is alsovery large, especially for displacement of a single smalltarget.

Frequency Doubling Perimetry

When a low spatial frequency sinusoidal grating (less than1 cycle/degree) undergoes high temporal frequency coun-terphase flicker (greater than 15 Hz), the grating appears tohave twice its real spatial frequency (i.e., there appear to betwice as many light and dark bars in the grating) (Fig. 2.49).This phenomenon, called the frequency doubling effect,was first described by Kelly (208,209). Because the fre-quency doubling stimulus incorporates a low spatial fre-quency and a high temporal frequency, it is ideally suitedfor stimulation of M-cell mechanisms and has been adaptedfor use as a screening test for glaucoma by Maddess andHenry (210). Johnson and Samuels (211) modified the origi-nal test procedure to perform frequency doubling perimetryof localized visual field regions. In its initial form, frequencydoubling perimetry evaluated 17 visual field locations (fourper visual field quadrant, each 10� in diameter, plus a stimu-lus presented to the central 5� of the visual field) throughoutthe central 20� radius of the visual field. In its current form(the Humphrey Matrix FDT perimeter), 54 and 72 test loca-tions matching the 24–2 and 30–2 grids of conventional


1 cycle/ degree or less

}

greater than 15 Hzcounterphase flicker

1 cycle/ degree or less

}

greater than 15 Hzcounterphase flicker

Figure 2.49. Schematic representation of the stimulus used in frequencydoubling perimetry.

automated perimetry are utilized. A contrast threshold is ob-tained for detection of the frequency-doubled stimuli at eachvisual field location. The sensitivity and specificity of fre-quency doubling perimetry are similar to those of conven-tional automated perimetry for detection of glaucomatousvisual field loss (sensitivity and specificity of 95% or better)(211–213) (Fig. 2.50). In addition, results obtained in pa-tients with nonglaucomatous optic neuropathies suggest thatfrequency doubling perimetry is also useful for evaluationof such patients (213, 214). Commercial versions of the fre-quency doubling perimetry test developed by Welch Allyn,Inc. (Skaneateles, NY) is available from Carl Zeiss Meditec(Dublin, CA).

Frequency doubling perimetry has several advantages asa clinical diagnostic tool. First, it is a rapid test. Second,

Figure 2.50. Comparison of results obtained for the Humphrey Field Analyzer and frequency doubling perimetry in a patientwith glaucomatous visual field loss.

patients prefer the test to conventional automated perimetry.Third, it has low test-retest variability. Fourth, the equipmentis small and portable and does not require a special roomwith controlled lighting. Fifth, it is unaffected by blur of upto 3 diopters for FDT using the 24–2 pattern and 6–7 diop-ters for the initial version with larger stimuli. Finally, pa-tients can wear their normal spectacle correction to take thetest, even if they have a bifocal added. The primary disadvan-tage of frequency doubling perimetry is that it is affectedby cataract, as are all tests of contrast sensitivity.

COLOR VISION

A comprehensive discussion of color vision is beyond thescope of this chapter. Instead, we will limit our discussionof this subject to an overview of normal color vision and itsunderlying physiologic mechanisms, congenital and ac-quired color vision deficiencies, the use and interpretationof common clinical color vision tests, and the diagnosticvalue of color vision testing in ophthalmic and neurologicdisorders. Several excellent sources are available (13,215,216) for those interested in a more thorough discussionof color vision, the history of color vision research, and adetailed account of color vision deficiencies in specific ocu-lar disorders. In particular, the book by Kaiser and Boynton(216) contains an especially interesting chapter pertainingto the history of color vision.

General Principles of Color Testing

From a clinical diagnostic standpoint, it is important todistinguish whether a color vision deficiency is congenitalor acquired (Table 2.5). Congenital color vision deficits areusually easy to classify using standard clinical color visiontests because color discrimination is usually impaired for a

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Principles and Techniques of the Examination of the Visual Sensory System

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