Low Vision EvaluationLow Vision Evaluation
Ms MB JAN- 24/01/2012
ContentContent
1. The difference between a low vision exam and a regular exam
2. The Case History3. Evaluating visual performance
4. Evaluating visual performancei. Visual acuityii. Visual field evaluationiii. Contrast sensitivityiv. Colour vision5. Objective refraction6. Subjective refraction7. Ocular health evaluation
OUTCOMESOUTCOMES
At the end of this lecture, learners should be able to:
Discuss the importance of a case history specifically for a low vision patient
Discuss specific questions that will be asked to a low vision patient
Describe the different techniques and charts used to measure a low vision VA (near, distance, aided, unaided etc.)
Discuss the need for evaluating visual fields in a LV patient
Discuss methods and techniques for evaluating visual fields in a LV patient
Discuss the need for evaluating contrast sensitivity in a LV patient
Discuss the need for evaluating colour vision in a LV patient
Discuss the methods and techniques used for evaluating colour vision in a LV patient
Discuss the objective refraction techniques available to the low vision optometrist
Discuss the technique and implications of radical retinoscopy
Discuss the method used for refracting a low vision patient
Analyze a low vision case based on a history, and then decide on and describe the most appropriate evaluation routine for a specific patient
Distinguish between a low vision refraction routine and a normal refraction routine
Explain the concept of JND (just noticeable difference) and be able to use it to test a low vision patient
The pre-evaluation information The pre-evaluation information sheetsheetIt sets clear boundaries on what
you will be able to doDraw up your own sheet in
practice
Information sheetInformation sheet
1. The appointment duration2. Schedule appointment around a
time when patient’s vision is stable
3. Bring with old glasses, magnifiers – even if not usable anymore
4. Think about specific problems the patient is experiencing
5. Start thinking in terms of goals – write down what you would like to achieve
6. Bring along special materials he/she want to be able to use (E.g. books)
7. Bring along a report from the ophthalmologist
8. Follow-up visits or training sessions with equipment may be necessary
9. State that there are no miracles, we will use your remaining vision effectively
The difference between a low The difference between a low vision examination and a regular vision examination and a regular exam exam
Give the differences and explaineach point given
Disadvantages of using Disadvantages of using phoropterphoropterWhy not phoropter?
Case HistoryCase HistoryNB. Very important, It has to be even more detailed
The patient interviewThe patient interviewThe successful patient interview
has 3 functions (Cohen-Cole)◦Gathering data to learn about the
patient’s problem◦Developing rapport, and responding
to the patient’s emotions◦Educating patients about their
problems, and motivating them to adhere to the prescribed treatment
Interview techniquesInterview techniquesBoth parties should be seated at
eye-to-eye heightSeating should be comfortableControl lighting – not too dim or
brightCarefully observe the patient
Use both open-ended and specific questions
May be emotionally chargedNote taking should be done subtly
Be alert to inconsistencies Take sufficient time that patient
doesn’t feel rushed BUT keep it brief – old people tire
more easily Use positive languageQuestion in a friendly, enthusiastic
manner
Adjust pace to that of patient.Don’t use medical jargon, explain
patient’s condition if they do not understand it
Never give false reassurancesPrimary aim is to help patient – don’t
fear to be inquisitive – but respect privacy too!
The purpose of the case The purpose of the case historyhistory
Why is it important to take LVcase history?
The real questions you want The real questions you want answered are:answered are:1. What does the patient want?2. What does the patient need?3. What is the real reason for the
patient’s visit?
Information requiredInformation required1. Basic identifying information
◦ Name, address etc
2. Who accompanied the patient?◦ Support system / self-sufficient?◦ Relative, friend, counselor, teacher
etc◦ Contact person◦ Provide insight into history
3. Referral source◦ Send thank you note◦ Reports
4. Diagnosis of eye condition◦ In patient’s own words◦ See if patient understands condition◦ Begin with patient education on
problems.
Visual historya. Durationb. Previous carec. Nature of vision loss (congenital or
acquired? Stable or progressive?)d. Fluctuation of vision
e. Problems with color visionf. Is there a preferred eye?g. Problem with glare or lighting?h. Current glasses / low vision aidi. Current visual capability (specific task-
related questions)i. Smallest print read? Newsprint Headlines Large print
ii. Able to watch television? ◦ What viewing distance?◦ Size screen?iii. Can you recognize faces at a distance?iv. Can you see well enough to get
around?
l) Family visual history
5. Medical historya) Undergoing treatment for medical
condition?b) Does the patient have a disease
with known ocular implications?c) Is there medical problems that
might affect the use of a LVA? (stroke)
d) Family historye) Allergies and drug sensitivitiesf) Medications (many systemic drugs
have ocular side-effects)
6. Employment or school history◦ Investigate the effect the visual loss
has on the work/school performance◦ Investigate the use of appropriate
devices to alleviate problems◦ Some older people might want to
continue their education
7. Avocations◦ Hobbies or activities
8. Social assessment◦ Does the patient live alone or with
family?◦ How is daily life affected by the vision
problem?◦ Does the patient have a support
network?◦ Is the patient’s independence
threatened?
10. General appearance of patient◦ Well groomed, clean or untidy?◦ Food stains – cannot see that level of detail◦ Poor grooming - emotional disorders such as
depression◦ Walk without assistance?◦ Mobility ◦ Does the patient look ill?
11.Patient goals (Chief complaint) Possibly the most important part of
the case history Allow a full elaboration of the visual
disabilities Patient’s new problem should be
fully investigated
After the patient has completed a list of complaints, several issues should be addressed regardless of the patient’s failure to mention thema. Distance visionb. Near visionc. Orientation and mobility skillsd. Glaree. Lifestyle
External evaluationExternal evaluationSome do this just after VA’s, but
depends on circumstances. Give an example
Brief look into the eyes, do not shine bright lights into the eye
Note the following about the eyes:◦Position of eyes (strabismus)◦Pupil – size, reaction to light,
appearance, ◦Cornea – opacities: size, density,
position◦Lens – opacities, position (especially IOL)◦Motility – strabismus, nystagmus,
restrictionsBinocular dysfunction is usually of
secondary importance
Evaluating visual Evaluating visual performanceperformance
Why?Why?Compare with normal
performance, or accepted standard (eg driving regulations)
Set a baseline for monitoring the condition
Quantify the patient’s own subjective impression of visual performance
Early detection and diagnosis of (other) visual disorders
Assessment of the benefits of an intervention (medical, surgical, rehabilitation) program
Predicting visual function in every day tasks
Visual acuityVisual acuity
Visual acuityVisual acuity1.Why do we want to accurately
measure acuity? 2. Limitations of VA measurement3. Factors affecting VA measurements4. Distance Visual Acuity5. Near Visual Acuity
Why do we want to accurately Why do we want to accurately measure acuity? measure acuity? i. It establishes a baseline from
which to monitor pathologyii. Used to predict the magnification
level of the optical devices that will be required to achieve the patient’s goals
iii. Often requested by other agencies to establish legal blindness, driving privileges, job eligibility etc.
Limitations of VA Limitations of VA measurementmeasurementi. The clinical acuity does not
give an accurate indication of the functional acuity. Explain
ii. Clinical measure of person’s ability to read letters under controlled circumstances
iii. It doesn’t always correlate with daily activities
iv. Function can be influenced by differences in contrast sensitivity, glare sensitivity, motivation and numerous other factors
v. VA can vary due to test setting, illumination, doctor-patient relationship and target contrast
Factors affecting VA measurements
How does each of the following How does each of the following factors affect VA factors affect VA measurement?measurement?i. Lightingii. Optotypeiii. Mental state of the patientiv. Instructions to patient/attitude /
encouragementv. Glare recoveryvi. Educational levelvii. Recognition/memory/speechviii. Motivation
Distance Visual AcuityDistance Visual Acuity
a. VA Notationsb. Acuity chart designc. Currently used chartsd. Measuring distance VA
a.a. VA NotationsVA Notations
1. Snellen◦ Either metric or imperial◦ We use imperial (feet)
2. LogMar (logarithm of the minimum angle of resolution)
3. Decimal: Snellen fraction4. Angular (specified in minutes of arc)
◦ Not used clinically
b.b. Acuity chart designAcuity chart design
The following aspects of chart design can be considered
i. Optotype –◦ style of print and selection of letters◦ Should yield equivalent results to
Landolt Cii. Number of letters per row
◦ Equivalent – equal task progression◦ 5 good clinically
iii. Sequence of Letters ◦ not form words/part of words
iv. Optotype Size◦ 0.1 logarithmic progression of
character size◦ Accurate measurements at both
standard and non-standard test distance
v. Letter spacing ◦ systematic
c.c. Commonly used charts Commonly used charts
1. Feinbloom Number Chart
Refer to your notes for advantages and disadvantages
Of this chart
2. Bailey-LovieAdvantages logMar format Equal number of
letters at each line
Can be used at any test distance
3. Projected cards4. Other
1. Lighthouse distance acuity card (available in our clinic)
2. Lighthouse symbol cards3. Designs for vision pediatric picture
chart4. University of Waterloo Chart5. ETDRS chart
d.d. Measuring Visual Measuring Visual AcuityAcuity
Use special low vision chartsUse a 10feet / 3 m working
distance, or lessEmphasize residual visionOffer encouragement and
realistic feedback
Watch for and encourage eccentric viewing
Let the patient attempt to read all letters on the chart, and look for scotomas
Record as Snellen fraction, e.g 10/700 To convert between feet and meter,
divide by 3.25 (feet to meter) or multiply by 0.3 (meter to feet)
Always measure the acuity correctly: “less than 6/60” is unacceptable
Recording VA Recording VA MeasurementsMeasurementsCan have a measurement
recorded as BEO (both eyes open) – distinguish from OU
Record the fractions read:10/240 + 2 of 10/200 + 1 of 10 / 180
If the patient is unable to If the patient is unable to identify any optotypes, which identify any optotypes, which designations are you going to designations are you going to use?use?
Near VANear VAThe measurement of Near VA is a
very important part of low visionMost low vision patients struggle
with reading, so magnification for near tasks is vital.
Near VANear VA
a. Specification of Nearpoint acuityb. Measuring near acuity with the
M system
a.a. Specification of Specification of Nearpoint acuity Nearpoint acuity
i. M notation◦ Method of choice◦ Metric notation◦ Represents the distance in meters at
which the target subtends an angle of 5’ of arc
◦ 1.00M subtends 5’ at 1m◦ Consistent, meaningful, flexible testing
distance
ii. N notation◦ Point size of lower case Time Roman
print◦ Standardized so that each point is 0.18
mm on the printed page◦ N10 is twice N5◦ Quite valid◦ Necessary to specify both test distance
and target size
iii. Point type◦ Actual print size in printers point notation◦ Size of slug, but not actual print size◦ Not a very good system
iv. Reduced Snellen◦ Characters subtend the same angle indicated
by the designated fraction at 20 feet◦ Specified test distance◦ Not 20 units, not a standard angle at 20
distance units◦ Cannot be used at any other distance◦ Useless - inflexible
Visual field evaluationVisual field evaluationThis another important aspect in
low vision patientDesirable to test all patient’s
fields, but not always possible or practical
Instruments and Instruments and techniquestechniques1.Confrontation test
◦Only a gross estimate of the peripheral field
◦Screening method◦Use light as a target
2. 2. Amsler gridAmsler grid
a. What is it?◦ Hand-held chart used to evaluate central 20°
of vision◦ Can identify early changes like
metamorphopsia or small central scotoma
b. What does it look like?◦ 20 blocks x 0.5mm each
c. How does it work? “Place a finely quared chart before an eye
suffering from an affection of the central region of the retina, and the patient will immediately point out spots and distortions which affect his/her vision”
Measures the central 20° of vision if the chart is held 28-30cms from the eye
d.d. Types of chartsTypes of charts
i. Standard chart * Every case, and usually sufficient
ii. Diagonal lines* Use with central scotoma
iii. Red on black standard chart Colour scotoma
iv. Spots only Reveals scotoma (no lines to be
distorted)
v. Parallel lines Use horizontally and vertically Shows metamorphopsia
vi. Parallel lines for reading Allows a more minute evaluation of
reading area
vii. Standard block with smaller reading area
Minute examination of juxta-central area Rectangle shows limit of fovea
e.e. General methodGeneral method
Testing distanceOptimal refractionClean, clear, well-lit chartNo ophthalmoscopy etc prior to
evaluationDo monocularly and then BEO to
check for interference/suppression
What chart?◦Start with grid◦Then use lines and spots
Do monocularly and then BEO to check for interference/suppression
f.f. Questions askedQuestions askedi. Do you see the white spot in the
centre of the squared chart?ii. 4 corners? 4 sides? Whole of the
square?iii. Network intact?iv. Lines straight + parallel?v. Anything else?vi. Plotting the distortions?
Colour visionColour visionPathological conditions like
glaucoma and ARMD can cause changes in colour vision, so it is necessary to evaluate this. ◦City University (not available in our
clinic )◦Isihara ◦Farnsworth D15
IsiharaIsihara
Tests for colour deficiency of congenital origin
Limited value in LV
Farnsworth D15Farnsworth D15
Available in our clinic
Check functional tests notes
Refraction Refraction Always obtain the best possible refraction with the best possible VA – to give the lowest magnification, why?
Objective refractionObjective refraction1. Autorefractors
◦ Limited use, due to media problems or eccentric viewing (off axis fixation)
2. Previous glasses◦ Can be a good starting point◦ Just make sure patient is using own
Rx!◦ Patient might have had ocular
surgery since glasses were prescribed
3. Keratometry◦ Useful with astigmatism – amount and
orientation of cyl◦ Patient may have difficulty fixating◦ Can be helpful in detecting irregular
corneal surfaces or irregular astigmatism
4. Retinoscopy◦ Very useful, especially if patient is a
poor responder◦ May be necessary to use radical
retinoscopy
Retinoscopy ◦Always do the ret in a trial frame◦If there is no initial response or no reflex
is seen, try using very large lens changes like +/- 5D, +/- 10D, +/- 20D
Radical retinoscopyRadical retinoscopyRadical retinoscopy means that
the working distance is drastically reduced (as close as 10cm)
Radical retinoscopy can also mean deliberate off-axis scoping to use any visible reflex – this will induce unwanted cylinder, but the results can be potentially valuable
Subjective refractionSubjective refraction
1 General conditions2 The trial frame3 The JND (just noticeable
difference)4 Spherical refraction5 Cylindrical refraction
General conditionsGeneral conditionsUse a 10feet or less working
distanceUse full illumination unless
otherwise indicated (e.g. patient with achromatopsia)
Use the low vision chart in subjective refraction
Always do a trial frame refraction
The trial frameThe trial frame
Why do we use it?
The refraction itselfThe refraction itselfUse standard methods and background knowledge to refine cylinder axis, power and sphere power
The JND (just noticeable The JND (just noticeable difference) difference) Essential conceptThe smallest dioptric step that a
patient is able to discriminateIt is senseless and frustrating to
use 0.25D steps when (because of the visual impairment) the patient can only notice a 1.00D change
Use the 10-feet equivalent as a rough starting point for JND
If the best VA is 10/100, the JND will be 1.00D
10/50 = JND of 0.50D
Spherical refraction Spherical refraction Use the tentative result from your
objective refraction as a starting point
Determine the JND-lens, and check the sphere value with that
“Better with the lens, or without it”, not “one or two”
Patients may have a poor, slow, variable response – could be due to pathology
Cylindrical refractionCylindrical refractionCheck the axis using a hand-held
Jackson Cross-cylinder of +/- 0.50D or +/- 1.00D if possible
You can also use rotation to blur/clear and let the patient rotate the axis her/himself
Cylinder power is checked in the normal way
Double check cyl power with direct
comparison (with or without) – if no subjective or objective improvement, it is not necessary to prescribe
Finally, double check the spherical component again – use bracketing (eg +0.50 and -0.50 should blur equally)
Ocular health evaluationOcular health evaluation
OPTIONS:◦Ophthalmoscopy◦Keratometry◦Tonometry◦Slitlamp ◦Von Herick◦Dilated fundus exam◦Binocular indirect ophthalmoscopy