Fall 2006Volume 9, Number 2
FACULTY PROFILE: Suresh Viswanathan
FEATURED REVIEW: A Brief Review of Visual Electrodiagnostic Techniques
BOOK NOTICE: Borish’s Clinical Refraction
MINI-REVIEW: Thirty-Day Continuous Wear of Silicone-Hydrogel Contact Lenses
CLINICAL RESEARCH: Does the Convenience of Having the Patient Hold theLens Flipper Affect Accommodative Facility Rates?
MINI-REVIEW: Functional Magnetic Resonance Imaging: Overview and Examplesof its Use in the Study of Vision
The Indiana University optometry faculty member profiled in this issue is Suresh
Viswanathan, who has been at IU since 2000. For the issue’s featured review, Suresh
writes about visual electrodiagnostic techniques. He gives an overview of ERG, EOG,
and VEP testing and discusses some recent advances in the field.
Many readers are very familiar with the book Clinical Refraction, by Borish, the third
edition of which was published in 1970. Now, thirty-six years later, the second edition of
Borish’s Clinical Refraction, edited by W.J. Benjamin, has been published. The history
of various editions of these books and their content are discussed.
Neil Pence provides an update of recent literature on thirty-day continuous wear of
silicone-hydrogel contact lenses. Also in this issue is a research report on the effect of
the patient rather than the examiner holding the flipper bar during lens rock
accommodative facility testing. And lastly, there is a brief review of a new technique for
the study of the brain and vision, functional magnetic resonance
imaging. We hope that the variety of articles in this issue will
provide some reading of interest to you.
David A. Goss
Editor
In This Issue
Correspondence and manuscripts submitted for publication should be sent to the Editor: David A.
Goss, School of Optometry, Indiana University, Bloomington, IN 47405 USA (or
[email protected]). Business correspondence should be addressed to the Production Manager:
J. Craig Combs, School of Optometry, Indiana University, Bloomington, IN 47405 USA (or jocombs
@indiana.edu). Address changes or subscription requests should be sent to Sue Gilmore, School
of Optometry, Indiana University, Bloomington, IN 47405 USA (or [email protected]).
Our appreciation is extended to Essilor of America for financial support of this publication.
Varilux® is a registered trademark of Essilor International, S.A
ON THE COVER: Three dimensional representation of the total response of the multifocalelectroretinogram across the central visual field - see Dr. Viswanathan’s article.
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Fall 2006Volume 9, Number 2
Table of Contents
TABLE OF CONTENTS
FACULTY PROFILE:Suresh Viswanathanby David A. Goss ................................................................................................. 24
FEATURED REVIEW:A Brief Review of Visual Electrodiagnostic TechniquesBy Suresh Viswanathan ....................................................................................... 25
BOOK NOTICE:Borish’s Clinical Refraction: The Namesake of the Classic Book Continues into a Second Edition by David A. Goss ................................................................................................. 30
MINI-REVIEW:Thirty-Day Continuous Wear of Silicone-Hydrogel Contact Lenses: What Have We Learned? by Neil Pence ........................................................................................................ 32
CLINICAL RESEARCH:Does the Convenience of Having the Patient Hold the Lens Flipper AffectAccommodative Facility Rates?by David A. Goss, Sara FitzGerald, and Gregory P. Hubbard ..................... 34
MINI-REVIEW:Functional Magnetic Resonance Imaging: Overview and Examples of its Use in the Study of Visionby David A. Goss ................................................................................................. 38
Statement of Purpose: The Indiana Journal of Optometry is published by the Indiana UniversitySchool of Optometry to provide members of the Indiana Optometric Association, Alumni of theIndiana University School of Optometry, and other interested persons with information on theresearch and clinical expertise at the Indiana University School of Optometry, and on newdevelopments in optometry/vision care.
The Indiana Journal of Optometry and Indiana University are not responsible for the opinions andstatements of the contributors to this journal. The authors and Indiana University have taken carethat the information and recommendations contained herein are accurate and compatible with thestandards generally accepted at the time of publication. Nevertheless, it is impossible to ensure thatall the information given is entirely applicable for all circumstances. Indiana University disclaimsany liability, loss, or damage incurred as a consequence, directly or indirectly, of the use andapplication of any of the contents of this journal. This journal is also available on the world wideweb at: http://www.opt.indiana.edu/IndJOpt/home.html
The author of the featured review in this
issue is Suresh Viswanathan, who joined
the Indiana University School of
Optometry faculty in 2000. Suresh
received a B.S. degree in Optometry
from the Elite School of Optometry,
in Madras, India, in 1990. The
B Optom. degree is the qualifying
degree for optometry practice in
India. It is a four year program with
a curriculum patterned after curricula in the
United States. The Elite School of Optometry
is thought by many to be the premier
optometry program in India. It was
established in 1985, and has had 280
graduates. Over 60 of their graduates have
gone on to complete graduate degrees, one of
them being Suresh Viswanathan.
The Elite School of Optometry was getting
started about the time Suresh graduated from
high school. He read about the program in the
local newspapers and started gathering
information about optometry and brochures
from various optometry schools. The wide
range of biological, physical, and clinical
sciences in optometry curricula as well as the
broad range of ongoing research in optometry
appealed to Suresh.
After completing optometry school, Suresh
worked for a year in the optometry department
at Sankara Nethralaya, a charitable eye
hospital in India. During that year, he also
assisted in some clinical research being done
at that institution. He completed an M.S.
degree in Clinical Optometry at Pacific
University in Forest Grove, Oregon, in 1992,
concentrating in binocular vision, vision
training, and low vision. His M.S. thesis
supervisor was Robert Yolton. He then went
to the University of Houston where he
completed a Ph.D. in physiological
optics/vision science in 2000. At the
University of Houston he specialized in the
area of retinal electrophysiology. His
dissertation research was supervised by Laura
Frishman. He also had the opportunity to
work with John Robson, Ronald Harwerth, and
Earl Smith while in graduate school.
At Indiana University, Suresh teaches
systemic and retinal physiology to optometry
students. He teaches topics in visual
neurophysiology to vision science graduate
students. Suresh also operates the School’s
clinical visual electrodiagnostic laboratory. He
is developing a reputation among his
colleagues of doing a good job of involving
optometry students in his research. He also is
advisor to some students who are pursuing
both O.D. and vision science M.S. degrees.
Suresh’s research efforts involve retinal
electrophysiology and trying to develop non-
invasive methods of evaluating retinal
ganglion cell function. His work trying to
identify how different retinal cell types
contribute to the electroretinogram (ERG) may
help to elucidate disease mechanisms of
glaucoma and other ocular neuropathies. He
is also examining the effectiveness of various
neuroprotective agents for maintaining retinal
ganglion cell function. Another direction in his
research is studying age-related changes in
the visual pathways and how the effects of
age-related degenerations may be minimized.
His work has been published in leading vision
science journals, including an article in the
July, 2006, special issue of Optometry and
Vision Science on glaucoma.
When Suresh is away from work, he
spends a lot of time with his children. His
daughter, Meghana, is four years old, and his
son, Neel, is three. Suresh’s wife, Tracy
Nguyen, graduated from optometry school at
the University of Houston, and is currently a
Ph.D. student in vision science at Indiana
University.
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Faculty Profile:Suresh Viswanathan, B. Optom., M.S., Ph.D.by David A. Goss, O.D., Ph.D.
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Visual electrodiagnostic techniques are
objective tests used to assess the functional
integrity of the retina, the optic nerve and
central visual pathways. The necessity for
electrodiagnostic tests arises when conventional
testing cannot provide adequate assessment of the
patient’s visual function. To properly use
electrodiagnostic tests practitioners must not only
realize when these tests will be beneficial to the
patients, but they must also be able to select the
appropriate tests and properly interpret the results.
This article provides an overview of the cellular
origins of some common visual electrodiagnostic
responses, their recording techniques and clinical
applications. Detailed information regarding these
methods can be found in general references.1
Electroretinogram (ERG)
The electroretinogram (ERG) is a test designed
to measure electrical potentials that arise from the
retina, usually in response to a full-field flash of
light (flash ERG) or to a large field pattern stimulus
(pattern ERG). The flash ERG provides an
objective indication of the overall retinal function
and reflects the summed electrical activity of
different groups of retinal cells.2 The ERG signal
recorded under dark-adapted (scotopic) condition
to a reasonably bright flash consists of three
components termed a-, b- and c-waves (Figure 1).
The negative-going a-wave is generated by rod
photocurrents3 and the positive-going b-wave by a
combination of depolarizing bipolar-cell currents
and bipolar-cell dependent K+ currents affecting
Müller cells.4-9 The c-wave (not shown) is the
sum of a very slow cornea-negative potential
arising from the distal portion of the Müller cells
and a slow cornea-positive component derived
from the retinal pigment epithelium.10,11
Contributions to the scotopic ERG from later
stages of retinal processing, specifically from
amacrine and retinal ganglion cells, have been
identified in the negative-going scotopic threshold
response (STR – not shown)12,13 that can be
elicited with very dim flashes under complete dark-
adaptation.
Under light adapted (photopic) conditions when
the rods are saturated the ERG response reflects
the electrical activity of the cells in the cone circuits
(Figure 2). The photopic a-wave is generated by
cone photocurrents14-16 with additional
contributions from hyperpolarizing cone bipolar
cells and perhaps horizontal cells.17 The photopic
b-wave results from the combined activity of
depolarizing and hyperpolarizing cone bipolar cells
and perhaps horizontal and Müller cells.18 The d-
wave (not shown) is a positive off response
component seen clearly with long duration flashes,
that may originate from the combined activity of
cone bipolar cells and photoreceptors.6 Recent
studies have shown that the slow negative
potential, the photopic negative response (PhNR),
that follows the b-wave (and if the flash duration is
long appears again after the d-wave) originates
from the inner retina probably as a consequence of
spiking activity of retinal ganglion cells.19
Also seen with special recording configurations
are oscillatory potentials (OPs) that appear as
wavelets superimposed on the ascending limb of
the b-wave (Figures 1 and 2). These potentials are
high-frequency, low amplitude components of the
ERG, with a frequency of approximately 100-160
Hz, to which both rod and cone systems contribute.
Animal studies indicate that OPs are generated in
the inner-retina by complex mechanisms.20, 21
Recording electrophysiological signals, such as
those associated with the flash ERG, involves
several basic steps. The patient usually is
stimulated with diffuse strobe flashes presented in
a Ganzfeld (a diffusing sphere). Appropriate
equipment can vary the duration, wavelength and
Featured Review: A Brief Review of VisualElectrodiagnostic Techniquesby Suresh Viswanathan, B.Opt., M.S., Ph.D.
FFiigguurree 11. Dark-adapted(scotopic) ERG responseillustrating the a-wave b-waveand oscillatory potentials(OPs).
FFiigguurree 22. Light-adapted(photopic) ERG responseillustrating the a-wave b-waveand oscillatory potentials (OPs)and the photopic negativeresponse (PhNR)
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frequency of the light flashes. The generated
signal is then detected through surface contact
lens electrodes, metallic fibers, or a foil strip placed
on the dilated and anesthetized eye. Signals from
the ocular electrode and another electrode either
on the fellow covered eye or placed elsewhere on
the body are differentially amplified and presented
on the visual display and recorded for further
analysis.
The flash ERG can be evaluated by comparing
the amplitude and latency of the a-wave and b-
wave components to expected values. Most of the
ERG measures change with the age of the patient,
so appropriate age norms must be used when
interpreting these results and the stimulus and
background-light sources must be periodically
calibrated. The flash ERG can provide important
diagnostic information on a number of retinal and
choroidal disorders including, among others,
congenital stationary nightblindness with myopia,
achromatopsia, X-linked juvenile retinoschisis and
Lebers’ congenital amaurosis. The flash ERG is
also of value in monitoring disease progression in
such disorders as retinitis pigmentosa,
choroideremia and cone-rod dystrophy.
Additionally, the ERG is of potential value in
determining retinal toxicity associated with drugs,
intraocular foreign body and vitamin A deficiency.
Loss of oscillatory potentials has been shown to
indicate retinal ischemia, which might occur with
the onset of diabetic retinopathy.
The pattern ERG (Figure 3) is voltage of much
smaller amplitude than the flash ERG and is
recorded to pattern-reversal stimulus. Pattern
ERG recordings in the clinical setting are
performed with high-contrast reversing
checkerboards or gratings of low temporal
frequency. The response consists of a prominent
positive component, P50 with a larger negative
component N95. The N95 is produced primarily by
retinal ganglion cells and the P50 has additional
contributions from more distal retinal neurons.22
Pattern ERGs have been used to assess ganglion
cell damage resulting from temporary occlusion of
central retinal artery, macular disease, retrobulbar
optic neuritis, glaucoma and several others. The
pattern ERG evaluation of central retinal function
complements the full-field ERG in the assessment
of patients with retinal disease and the different
effects of optic nerve and macular disease on the
pattern ERG considerably improves the accuracy
of interpretation of an abnormal visually evoked
potential (VEP), facilitating the electrophysiological
distinction between optic nerve and macular
dysfunction.
Electrooculogram (EOG)
Electrooculography (EOG) is another objective
test of retinal integrity. It is particularly suited for
testing the status of the retinal pigment
epithelium,23 but it evaluates certain other parts of
the retina as well. Like the ERG it is a mass cell
response and therefore it generally does not allow
fine discriminations to be made about the
functional status of small retinal areas such as the
macula. It is less difficult to conduct an EOG than
an ERG because corneal electrodes are not
needed. EOG testing does, however, require a
reasonable degree of patient competence because
targets must be fixated accurately.
For EOG recordings, following dilation of the
pupil, five skin electrodes are attached to the
patient – one at each canthus and a reference
electrode is placed at a remote location. The
patient is asked to alternate fixation between two
target lights 30 degrees apart. This produces an
oscillating voltage at the electrodes, which is
amplified and presented on a visual display. The
FFiigguurree 33. Pattern ERG responses to pattern-reveral stimuliillustrating the prominent positive (P50) and later negative (N95)components.
FFiigguurree 44..Electrooculogram(EOG) potentialsas subject alternatesgaze between left andright under dark-and light-adaptedconditions.
voltage is recorded for about 15 minutes in the
dark, then 15 minutes in the light (Figure 4).
In the eye’s resting (dark-adapted) state,
normally there is a fixed potential difference
between the cornea (which is positive) and the
back of the eye. This standing potential which is
produced largely by the pigment epithelial cells –
varies with time in the dark, and a minimal value is
reached 5 to 15 minutes after the lights are
extinguished. When the lights are turned on the
potential increases for about 5 to 15 minutes until a
peak is reached. This increase is mediated by light
striking the receptor cells and probably also
involves activity of cells in the middle retinal layers.
By dividing the maximum potential recorded during
light adaptation (the light peak) by the minimum
standing potential found during dark adaptation
(dark trough), a ratio called the Arden Index (AI)
can be calculated.24 This value is commonly used
as a clinical indicator of eye health. An abnormal
AI ratio (lower than what is expected for a patient’s
age) indicates a widespread dysfunction of the
retinal pigment epithelium or other retinal
elements. Its use in hereditary macular diseases,
such as Best macular dystrophy and the various
pattern dystrophies, is particularly appropriate. Its
value in the various stationary and progressive
night-blinding disorders seems questionable,
because the ERG either provides more
diagnostically definitive information or allows the
investigator to predict what the EOG findings are
likely to be.
Visually evoked potential (VEP)
The visually evoked potential (VEP) is a signal
that is generated by the visual cortex in response
to visual stimulation.25 The recording electrode is
placed over the scalp, with the main signal
detected over the occipital region.26 Because the
occipital area of the cortex predominantly
subserves macular function, the VEP signal is
mainly derived from the macular region. It has
been estimated that the central 2 degrees of visual
field contributes 65% of the VEP response; in
comparison the ERG which is thought to represent
2% of the total response. The VEP response itself
is of very small magnitude as compared to the
normal electroencephalographic noise so that it
must be specially processed before it can be
analyzed. A pattern stimulus similar to that used for
the pattern ERG gives good response. A typical
waveform derived from a slowly repetitive stimulus
(Figure 5) contains a negative component with a
latency of approximately 75 ms (N75) that is widely
believed to reflect the activity of striate cells, while
the most common positive potential with latency of
100 ms (P100) is thought to originate in the
extrastriate areas 18, 19. 27-29 The VEP implicit
times are indicators of the time between stimulus
presentation and the response of the cells in the
visual cortex. An increase in the implicit time of
VEP components often is regarded as indication of
optic neuritis, which can be the result of
demyelinating disease such as multiple sclerosis.
However because latencies generally increase with
age, evaluation of latencies should be made with
respect to appropriate age norms. VEP amplitudes
are quite variable and thus limit the usefulness of
the procedure that depends on these
measurements. Some of the other applications of
the VEP include assessment of visual system
patency, objective determination of visual acuity
and refractive error, objective color vision testing
and objective visual field estimation.
Recent advances in ERG and VEP testing
The focal ERG is an extension of the full-field
ERG technology and uses a focal test stimulus
centered within a steady surround to elicit
submicrovolt responses from regions as small as 3
degrees. While in principle it will be possible to
record focal ERGs from multiple regions across the
retina to determine the topography of retinal
dysfunction, it is not practical due to time
constraints. This limitation of the standard focal
ERG can be overcome by employing the multifocal
technique of ERG recording that was developed by
Sutter and co-workers.30 This technique makes it
possible to record simultaneous ERG responses
from multiple retinal areas within a short duration.
Visual stimulus is displayed on a video monitor
in hexagonal arrays (Figure 6A). Each element in
the array is stimulated with the same
pseudorandom sequence of dark and light but the
sequence is lagged by different amounts for each
element. The response of each element in the
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FFiigguurree 55. Visually evoked potentials (VEP) potentials to pattern-reversal stimuli illustrating the N75, P100 and N135 components.
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array (Figure 6B) is then computed as the cross
correlation between the m-sequence and the
response cycle and the response can be derived in
kernels with increasing complexity. The multifocal
VEP is an extension of the same technique that is
used to record simultaneous cortical responses to
focal stimulation of multiple retinal locations. The
visual stimulation involves patches of contrast
reversing checkerboards (Figure 7A) that results in
an array of VEP responses from many regions of
the visual field (Figure 7B). The multifocal ERG
and VEP technology is still in its infancy. Studies
at this time indicate that the multifocal ERG could
be of use to detect regional defects in outer retinal
(photoreceptor and bipolar cell) disorders that are
not sufficiently extensive to significantly reduce the
full-field ERG31 and the multifocal VEP appears to
be a better candidate for studying regional
changes in retinal ganglion cell/optic nerve
diseases.32 These electrodiagnostic techniques
could be potentially powerful clinical tools for
diagnosis and monitoring treatment efficacies if
better methods of stimulus presentation, signal
analysis and improved recording conditions are
developed in the future.
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FFiigguurree 77. Cortically scaled dart board stimulus used for recordingmultifocal VEP (left) and representative first slice of second orderkernel response array (right).
FFiigguurree 66.. 103 hexagonal array stimulus used for multifocal ERGrecordings (left) and representative first order kernel response array(right).
......................................................................................IInnddiiaannaa JJoouurrnnaall ooff OOppttoommeettrryy ...... FFaallll 22000066 ...... VVooll 99,, NNoo.. 22...... ppaaggee 2299
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response. Vis Res 1992 ;32:433-446.
31. Hood DC. Assessing retinal function with the
multifocal technique. Prog Retin Eye Res
2000;19:607-646.
32. Hood DC, Greenstein VC. Multifocal VEP and
ganglion cell damage: applications and limitations for
the study of glaucoma. Prog Retin Eye Res
2003;22:201-251.
Borish’s Clinical Refraction:The Namesake of the Classic Book Continues into aSecond Editionby David A. Goss, O.D., Ph.D.
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The second edition of Borish’s Clinical
Refraction, edited by William J. “Joe”
Benjamin, was published in 2006, with Irvin
M. Borish continuing from the first edition in his
role as consultant. The book was published by
Butterworth-Heinemann-Elsevier. It is a 1694
page tome full of the
latest information in
optometry.
The roots of this
book can be traced to
the 266 page book
Outline of Optometry
published by Borish in
1938 in an 8.5 inch by
5.5 inch format. The
publisher of that book
was V.J. LeGros and
Co. of Chicago, with
the copyright held by
the Northern Illinois
College of Optometry
(NICO). At the time,
Borish was Associate
Professor of
Optometry at NICO and Assistant Director of their
Clinic. The book included a two page introduction
by William B. Needles, President of NICO. In the
preface, Borish acknowledged assistance from
NICO colleagues Needles, Ernest Occhiena, W.
Jerome Heather, William B. Whitehead, Charles A.
Benson, and Bernard E. Vodnoy. The book
consisted of 21 chapters: Ophthalmic Lenses and
Prisms; Preliminaries to Refraction; Subjective
Testing; Convergence, Accommodation, and
Phorometry; Hyperopia; Myopia; Astigmatism;
Anisometropia; Presbyopia; Anomalies of
Refraction; Eyestrain; Subjective Accessory
Techniques; Retinoscopy; Dynamic Retinoscopy;
Ophthalmoscopy; Perimetry and Color Field
Analysis; External Ocular Examination and
Transillumination; Prescription of Bifocals; Tinted
Lenses; and Monocular Visual Pattern and
Strabismus. The book was in an outline format
with minimal reference citations. There was a two
page bibliography which listed mainly books. The
book was used as a textbook by several classes of
NICO students.
In 1944, Borish left NICO and set up practice
in Kokomo, Indiana. The next year World War II
ended, and in the next few years returning soldiers
swelled the ranks of optometry classrooms. The
remaining copies of Outline of Optometry quickly
sold out. The first edition of Clinical Refraction by
Borish, published in 1949, filled the void.
The first edition of Clinical Refraction, 431
pages in length, was published by Professional
Press of Chicago. It, like Outline of Optometry,
had an outline format. In the preface, Borish
acknowledged various types of assistance from
Glenn Fry and Henry Hofstetter of Ohio State, Carl
Shepard of NICO, and Kenneth D. Dutton, a
practitioner in Kokomo. Twenty-five chapters were
organized into five sections: The Refractive Status
(7 chapters); Preliminary Examination (5 chapters);
Refraction (5 chapters); Analysis and Prescription
(4 chapters); and Monocularity (4 chapters).
Reference citations appeared at the ends of
chapters. The title page indicated that the book
contained 111 illustrations.
The second edition of Clinical Refraction by
Borish was published in 1954, again with
Professional Press as the publisher. The names of
the five sections and the 25 chapters remained the
same. The outline format was retained, and the
text expanded to 576 pages. There was greater
use of reference citations in the second edition,
with some chapters having over 40 references. It
contained 137 illustrations.
In 1970, Borish published the third edition of
Clinical Refraction. The publishing company was
again Professional Press of Chicago. While the
first two editions were widely used as textbooks, it
was the third edition that became known as the
comprehensive and authoritative source of
optometric information, sometimes being referred
to as “optometry’s bible.”1 Its extensive use of
reference citations also made it valuable to
researchers wishing to consult the primary
literature. Survey respondents asked to list what
they thought were the most important optometry
books of the twentieth century mentioned Clinical
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Refraction more often than any other book.2
The third edition increased significantly not
only in number of pages (to 1381), but also in
physical dimensions. The first two editions were
approximately 9 inches by 6 inches, and the third
edition was 10.5 inches high by 8.5 inches wide.
The outline format was continued in the third
edition to, as Borish stated in the preface, “permit
the use of the book as both a text for the student
(by judicious selection and direction of his
instructor to specific sections and topics) and as a
reference by the practitioner or researcher.”
For the third edition, Borish enlisted the aid of
a number of collaborators. Six persons were listed
as co-authors: M. Greenberger, Gordon G. Heath,
William M. Ludlam, Alfred A. Rosenbloom, M.D.
Sarver, and Bradford W. Wild. Fourteen persons
were listed as collaborating editors: Merrill J. Allen,
William R. Baldwin, Frank Brazelton, John H.
Carter, Ronald W. Everson, H.M. Fisher, Merton C.
Flom, William M. Ludlam, Meredith W. Morgan,
Rogers W. Reading, Max Schapero, Charles R.
Shick, Jerald Strickland, and Sidney Wittenberg.
Eight of these collaborators were Indiana University
alumni and/or faculty members.
The third edition featured 32 chapters in five
sections: Refractive Status of the Eye (8 chapters);
Preliminary and Adjunct Examination (7 chapters);
Refraction (5 chapters); Analysis and Prescription
(8 chapters); and Monocularity and Strabismus (4
chapters). The introductory chapter in the
refractive status section in the second edition was
expanded from 16 pages in one chapter to 82
pages in two chapters in the third edition. Six new
chapters were added: Tonometry; Color Vision
Testing, co-authored by Heath; Problems of
Aphakia; Vision with Contact Lenses, co-authored
by Sarver; Low Vision Aids, co-authored by
Rosenbloom; and Ocular Pharmacology, co-
authored by Greenberger. The third edition went
through five printings, changing to a two volume
format with the second printing in 1975.
In 1998, sixty years after the publication of
Outline of Optometry and 28 years after the
publication of the third edition of Clinical Refraction,
a new book prepared in the spirit of the
comprehensiveness and authority of Clinical
Refraction was published. It was titled Borish’s
Clinical Refraction, with William J. Benjamin as
editor and Borish as consultant. The 1255 page
book contained 33 chapters in five sections:
Principles (5 chapters); Adjunct Examinations (11
chapters); The Refraction (4 chapters); Analysis
and Prescription of Optical Corrections (6
chapters); and Special Conditions (7 chapters).
The 46 authors of the various book chapters
represented all 17 optometry schools in the United
States, as well as other institutions. Benjamin
authored or co-authored six chapters, and Borish
wrote two chapters with Benjamin. Twelve of the
other 44 authors were Indiana University alumni
and/or faculty members. The book included 956
illustrations, many of them in color. There had not
been any illustrations in color in Clinical Refraction.
This book also differed from Clinical Refraction in
that it did not incorporate an outline format. The
success of this book led to the publication of a
second edition this year.
The second edition of Borish’s Clinical
Refraction provides updated information and
incorporates three completely new chapters,
reflecting the advances in optometric science and
practice. It retained the organization into five
sections as in the first edition. The second edition
is 1694 pages long. The use of color illustrations
was increased in the second edition, with color
even being used in tables, graphs, and headings,
making for a visually appealing book. Like the first
edition, the second edition is about 11 inches high
and 9 inches wide. In addition to Benjamin and
Borish, there are 53 authors for the second edition,
14 of them Indiana University alumni and/or faculty
members. Readers should be able to find not only
a great deal of information in this book, but also
references for the primary literature. Many of the
37 chapters have over 100 reference citations and
some have over 300 references. As Joe Benjamin
notes in the preface to the book, it will keep the
name Borish “associated with clinical refraction well
into the 21st century.”
References
1. Clinical Refraction at 50: Team takes “optometry’s
bible” into new era. AOA News July 19, 1999; 38(2):11-
12.
2. Goss DA, Penisten DK. Most important 20th century
optometry books. Hindsight: Newsletter of the
Optometric Historical Society 2004; 35:36-40.
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When the FDA first approved the overnight
use of contact lenses for more than six
nights, it did so with some concern about
the risk of infection. From experience with
previous extended wear approvals, it was clear
that much larger, longer-term studies were
required to get a good estimation of the risk of
microbial keratitis (MK). Therefore, when Night &
Day (CIBA Vision) and PureVision (B&L) soft
contact lenses were approved for 30-day
continuous wear (CW) in late 2001 and the
Menicon Z (Menicon) GP contact lens soon after,
the FDA required three year post-market studies
be done for each.
The first of these studies to be released
evaluated the Night & Day lens. CIBA contracted
with Johns Hopkins to oversee their three year
study. Over 6,000 patients were entered in the
CW study which included 131 clinical sites. In the
principal report of the findings regarding MK
incidence by Schein et al.1 The total rate of MK
was 0.18%. The rate of MK that resulted in a loss
of best corrected vision was 0.036%, while the rate
of MK with no resultant effect on visual acuity was
0.144%.
So what do we learn from these data? One
useful analysis is to compare the results to the
rates previously established for seven day
extended wear of lower Dk hydrogel lenses. A
number of studies exist, but the best and most
quoted is that done by Schein et al.2 They found
extended wear of contact lenses was 10-14%
higher risk of MK than daily wear. Others found
around a five fold increased risk. The current
study is certainly in that 5x risk neighborhood.
Therefore, in CW for 30 days the risk of MK
compares very favorably, and we can safely say
the risk is not increased for CW of silicone-
hydrogel lens when compared to seven day
extended wear with hydrogels. It should also be
noted, however, that the risk is also not terribly
different. Some of the early estimations of a
greatly reduced risk of infection may not have held
up. Other complications and problems are greatly
helped by the increased oxygen supplied by some
of the silicone-hydrogel lenses, but the risk of
infection is not greatly reduced. Patients and
practitioners need to be well educated and alert to
any early signs of infection.
A second comparison of interest is a look at the
risks with other correction options such as
refractive surgery. The main serious complication
has to be loss of best corrected vision. Many of
the published rates for refractive surgery are
studies done in the early years of the various
procedures, so they are undoubtedly too high
compared to today. When looking at only recent
studies (last two years), the rate of loss of best
corrected vision is still somewhere between 0.8%
and 6%.3-5 The 0.036% rate of CW causing loss
of vision is obviously much less, and even taken
over many more three year periods, CW would
appear to be at least as safe of a correction option
as refractive surgery.
Finally, the other significant finding reported in
this first three year post-market study was the
incidence of experiencing an infiltrative event. The
incidence of symptomatic infiltrative events was
2.6% per lens wear year. Since this is much
higher than the 0.176% rate of MK, most of the
infiltrates seen were inflammatory in origin as
opposed to infectious. An analysis of these
infiltrative cases by Chalmers identified a number
of risk factors for infiltrative keratitis (IK).6
Persons under the age of 25 had 1.65 times
greater risk, while those over 50 had a 2.01 times
greater rate of IK. Patients with refractive errors of
greater than 5 diopters were at 1.57 x greater risk.
The site or location of the office where they were
seen was also slightly significant, indicating
possible geographical effects, or quite possibly
differing screening and patient selection criteria of
various practitioners. Finally, there was a trend for
smoking to be related to an increased risk of IK,
but not at a strong significance level. With greater
numbers of events, however, this might prove to be
a risk factor as well. Knowing the variables that
put patients at higher risk for adverse events
should help practitioners in selecting the most
appropriate candidates for CW.
Related to the above study, a second
investigation concerning the CW of Night & Day
Thirty-Day Continuous Wear of Silicone-Hydrogel Contact Lenses: What Have WeLearned?by Neil Pence, O.D.
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contact lenses involved 317 patients enrolled at 19
different sites.7 The 2006 ARVO poster reported
the incidence of infiltrates as 5.7% in the first year,
8.5% through two years, and 10.3% for the entire
three year period. One important finding in this
report was that the presence of corneal staining or
increased limbal redness at a previous visit
represented an increased risk of developing IK.
Practitioners should be aware of the possible
significance of these findings in their CW patients.
In a second analysis of the results from this
investigation, Dillehay et al.8 reported the
incidence of various adverse events other than IK.
They found average incidence rates over the three
years for things like SEAL’s or Epithelial Splits
(0.13%), GPC (0.10%), CLPU (0.27%) and CLARE
(0.10%). It is interesting to note that some of these
are less than those reported in the initial FDA
submission to gain panel approval for CW. One of
the principal reasons is believed to be the
introduction of the steeper base curve after much
of the initial study had been completed. Adverse
events have been found to be greater if the lenses
are a little too loose, which the 8.6 base curve was
in the majority of eyes, so the 8.4 base curve has
been associated with lower complication rates.
Hopefully, the information gained from these
extensive post-market studies of the three CW
contact lenses will be very useful. The increased
knowledge gained from them should help
practitioners better select and monitor CW
patients. Knowing the patients most at risk and
how to better screen for and detect them, ideally
we would then be able to even reduce these
incidence rates. To date these studies show that
the CW risk compares very favorably to the risks of
other non-spectacle correction options, but also
serve to remind practitioners that they are not risk
free.
References
1. Schein OD, McNally JJ, Karz J, et al. Incidence of
MK among wearers of a 30-Day silicone-hydrogel
extended wear contact lens. Ophthalmol 2005; 112:
2172-2179.
2. Schein OD, Glynn RJ, Poggio EC, et al. The relative
risks of ulcerative keratitis among users of daily wear
and extended wear soft contact lenses: A case-control
study. N Engl J Med 1989; 321:773-778.
3. Esquenazi S, Bui V. Long-term refractive results of
myopic LASIK. J Refract Surg 2006; 22:54-60.
4. Gailitis RP. Comparison of LASIK outcomes with the
Alcon LADARVision4000 and the VISX S2 excimer
lasers using optimized nomograms. J Refract Surg
2005;21:683-690.
5. Spadea L, Sabetti L, D’Alessandri L, Balestrazzi E.
Photorefractive keratectomy LASIK correction of
hyperopia: 2 year follow-up. J Refract Surg 2006;
22:131-136.
6. Chalmers R. Who gets infiltrates in continuous wear
contact lenses? Presented at the CIBA Vision Educators
Meeting. San Antonio, Texas, March 2006.
7. Szczotka-Flynn L, et al. Predictive Factors for
Corneal Infiltrates with Lotrafilcon A Silicone-Hydrogel
Lenses. ARVO Poster #88/B376. May 2006.
8. Dillehay S, Long W, et al. Annual incidence reports
for adverse events in a 36 month trial with a silicone-
hydrogel soft contact lens. Presented at the CIBA Vision
Educators Meeting. San Antonio, Texas, March 2006.
Neil Pence is a 1979 graduate of the IndianaUniversity School of Optometry. He is a member ofthe Indiana University optometry faculty, servingprimarily in the Contact Lens Clinic. He maintainsan optometry practice in Columbus, Indiana. He hasgiven numerous continuing education courses oncontact lenses and related topics.
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Accommodative facility testing is an important
component of the evaluation of
accommodation and vergence function.1-5
The current clinical standard for testing lens rock
accommodative facility involves using +/- 2.00 D
lenses with 20/30 letters at 40 cm from the patient
with testing continuing for one minute. The
number of flips in one minute is divided by two to
yield a rate expressed in cycles per minute (cpm).
Table 1 summarizes the results of normative
studies using those testing parameters. While the
results of the studies show quite a bit of variability,
rates that are often given as cut-offs for abnormal
function for older schoolchildren and young adults
up to about 30 years of age are less than 11 cpm
monocularly and less than 8 cpm binocularly.
Reanalysis of data from García et al.8 found the
subjects with accommodation and/or binocular
dysfunctions in that study were best distinguished
from normal subjects with monocular rates less
than 11 cpm or binocular rates less than 10 cpm or
monocular rates more than 4 cpm greater than
binocular rates.10
There are multiple variables involved when
conducting accommodative facility testing.
Accommodative facility rates are increased when
letter size is increased, lens powers are
decreased, or test distance is decreased.9,11
Therefore, it is important to use consistent testing
procedures. In all of the studies listed in Table 1,
the testing was done with the examiner holding the
lens flipper. Students learning accommodative
facility testing procedures often find it convenient to
have the patient hold the lens flipper. They ask if
Does the Convenience of Having the PatientHold the Lens Flipper Affect AccommodativeFacility Rates? by David A. Goss, O.D., Ph.D., Sara FitzGerald, B.S., and Gregory P. Hubbard, B.A.
Authors Numbers ofSubjects
Ages ofsubjects in
years
Mean rates in cpm (SD in parentheses)
Burge (1979) 30 6 to 30 With polarizers, OU, 14.1 (8.5)
Zellers et al.(1984) 100 18 to 30
OD, 11.6 (5.0)OS, 11.1 (5.3)OU, 7.7 (5.2)
Hennessey et al.(1984) 50 8 to 14
Symptomatic subjects, OD, 8.6 (5.5)Symptomatic subjects, OS, 9.2 (6.5)Symptomatic subjects, OU, 4.0 (6.0)
Asymptomatic subjects, OD, 11.8 (6.4)Asymptomatic subjects, OS, 12.8 (7.2)Asymptomatic subjects, OU, 7.86 (8.0)
Scheiman et al.(1988) 395 6 to 12
6 year olds, OU, 2.8 (2.4)7 year olds, OU, 3.4 (2.7)8 year olds, OU, 4.4 (2.4)9 year olds, OU, 5.4 (2.3)10 year olds, OU, 4.7 (2.4)11 year olds, OU, 5.0 (2.4)12 year olds, OU, 4.9 (2.6)
Garcia et al.(2000) 48 10 to 30
Accommodative dysfunction, OU, 7.5 (3.2)Binocular dysfunction, OU, 5.2 (3.8)
Acc. or Binoc. dysfunction, OU, 7.1 (4.1)Normals, OU, 13.1 (2.5)
Loerzel et al.(2003) 50 21 to 35 OU, 11.6 (3.4)
TTaabbllee 11.. Studies of lens rock accommodative facility rates with +/-2.00 D lenses, 20/30 test letters at 40 cm, with a 1 minutetesting period. 2,4,6-9
that change in procedure affects test results. It
seems logical to assume that such a change in
testing procedure would affect the results, but it
does not appear that there any previous studies in
the literature on that question. The purpose of this
study was to test whether binocular lens rock
accommodative facility rates differ when subjects
hold the lens flipper from when the examiner holds
the lens flipper.
Methods
Study participants included 45 subjects ages
18 to 30 years as of their last birthday. The
exclusion factors were strabismus seen on the
cover test at near and best corrected visual
acuities less than 20/20 at near in each eye. Odd
numbered subjects started the testing holding the
flipper bar. The even numbered subjects started
with the examiner holding the flipper bar. A
standardized script was used for instructions given
to each of the subjects participating in the study.
The subjects were asked to hold the test card and
look at the near visual acuity target located at a
distance of 40 cm. Two sets of lenses were (+/-
2.00 D) placed in the flipper bar. The subject was
asked to read one letter aloud on the near target’s
20/30 line per flip. Measurements were recorded
based upon the number of cycles (one cycle
defined as two separate flips) the subject
completed in one minute. The subject completed
the testing after a ten minute break by performing
the procedure utilizing the other method of
examiner/subject holding the flipper bar.
Results
Summary statistics for examiner vs. patient
flipper rates are provided in Table 2. The data
points in the scatterplot in Figure 1 appear to
suggest that the rates for examiner holding the
flipper and subject holding the flipper were fairly
close for most subjects. The coefficient of
correlation was 0.82. The mean examiner flipper
rate was 10.9 cpm (SD=3.5), while the mean
subject flipper rate was 10.7 cpm (SD=3.6). The
paired t-test did not show a statistically significant
difference between examiner holding and subject
holding the flipper (t=0.75). The mean difference
between the rates was 0.2 cpm (SD=2.1). The
range of differences of rate for examiner holding
the flipper minus the rate for the subject holding
the flipper was -5.0 to +4.5 cpm. The graph in
Figure 2 is a plot of difference between the two test
procedures as a function of the average of the two
test results. A pattern of correlation in such a plot
would suggest a difference between two test
results which varies depending on whether the
findings are high or low. There was no such
correlation here (r=0.08).
Because most of the subjects in this study
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TTaabbllee 22.. Summary statistics of facility rates in cycles per minute forthe 45 subjects with the examiner holding the lens flipper bar andthe subject holding the lens flipper bar.
Examiner Subject
Range 4.5-19 3.5-19
Mean 10.9 10.7Median 11 10.5
St. Deviation 3.5 3.6
FFiigguurree 11.. Scatter plot of results with examiner vs. patient flipping the flipper bar.
FFiigguurree 22.. Scatter plot of difference of rate with examiner holding the flipperminus rate with subject holding the flipper as a function of the average of thosetwo findings.
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were optometry students, many of whom have
learned accommodative facility testing procedures,
it may be asked whether familiarity with testing
methods could have affected the results. A sub-
analysis was performed with only first year
students who have not learned how to do
accommodative facility testing. Summary statistics
for examiner vs. patient flipper rates for this sub-
analysis are given in Table 3. A scatterplot of data
points for the rates for examiner holding the flipper
and subject holding the flipper is shown in Figure
3. The coefficient of correlation was 0.66. The
mean examiner flipping rate was 11.0 cpm
(SD=3.0), and the mean subject flipping rate was
10.7 cpm (SD=3.4). The paired t-test did not show
a statistically significant difference between
examiner holding and subject holding the flipper
(t=0.52). The mean difference between the rates
was 0.3 cpm (SD=2.7). The range of differences of
rate for examiner holding the flipper minus the rate
for the subject holding the flipper was -4.5 to +4.5
cpm. Figure 4 is plot of difference between the two
test procedures as a function of the average of the
two test results, which did not show a significant
correlation (r=0.19).
Discussion and Conclusions
Previous studies have shown that changes in test
variables such as lens powers, subject age, test
distance, letter size, and presence or absence of
suppression control will affect the lens rock facility
rates obtained. It does not appear that the variable
of whether the subject or the examiner holds the
lens flipper has been studied previously. Having
the patient hold the flipper may afford some
convenience and may allow the examiner to
observe the patient more closely during testing.
Because the kinesthetic input of handling the lens
flipper might affect proximal accommodation and
because differences in reaction time in having the
subject or examiner flipping the lenses could affect
results, it might be expected that rates would be
different with a change in the person handling the
lens flipper. However, this study did not show a
significant difference in rates between the
examiner controlling the flipper bar and the subject
controlling the flipper bar.
References
1. Pierce JR, Greenspan SB. Accommodative rock
procedures in VT- A clinical guide. Optom Weekly
1971;62:753-757, 776-780.
2. Zellers JA, Alpert TL, Rouse MW. A review of the
literature and a normative study of accommodative
facility. J Am Optom Assoc 1984;55:31-37.
3. Hennessey D, Iosue R, Rouse M. Relation of
symptoms to accommodative infacility of school-aged
children. Am J Optom Physiol Opt 1984;61:177-183.
4. McKenzie K, Kerr S, Rouse M. Study of
accommodative facility test reliability. Am J Optom
Physiol Opt 1987;64:186-194.
FFiigguurree 33.. Scatter plot of examiner vs. patient flipping the flipperbar for inexperienced subjects.
Examiner SubjectRange 4.5-16 6-19Mean 11 10.7
Median 11.5 10.3St. Deviation 2.95 3.4
TTaabbllee 33.. Summary statistics of facility rates in cycles per minute forthe inexperienced subjects with the examiner holding the lens flipperbar and the subject holding the lens flipper bar.
FFiigguurree 44.. Scatter plot of difference of rate with examiner holding theflipper minus rate with subject holding the flipper as a function of theaverage of those two findings for the inexperienced subjects.
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5. Wick B, Yothers T, Jiang B, Morse S. Clinical testing
of accommodative facility: Part I. A critical appraisal of
the literature. Optom 2002;73:11-23.
6. Burge S. Suppression during accommodative rock.
Optom Monthly 1979; 79:867-872.
7. Scheiman M, Herzberg H, Frantz K, Margolies M.
Normative study of accommodative facility in elementary
schoolchildren. Am J Optom Physiol Opt 1988;65:127-
134.
8. García A, Cacho P, Lara F, Megías R. The relation
between accommodative facility and general binocular
dysfunction. Ophthal Physiol Opt 2000;20:98-104.
9. Loerzel R, Tran L, Goss D. Effect of lens power on
binocular lens flipper accommodative facility rates. J
Behav Optom 2003;14:7-9.
10. Goss DA. Accommodative facility testing as an
indicator of accommodative and binocular dysfunctions.
Indiana J Optom 2001;4:36-39.
11. Siderov J, Johnston AW. The importance of the test
parameters in the clinical assessment of accommodative
facility. Optom Vis Sci 1990;67:551-557.
David Goss is in his fifteenth year as a member of theIndiana University faculty. Sara FitzGerald and GregHubbard are members of Indiana UniversityOptometry Class of 2007.
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Brain imaging has become very useful as a
diagnostic and research tool. One common
imaging technique is magnetic resonance
imaging (MRI). MRI uses a very high power
magnet, radio frequency signals, and computer
processing to produce anatomical images. The
MRI magnet causes atomic nuclei in the tissue
being scanned to align in a particular way. A radio
frequency signal alters that signal and when it
stops, the realignment of the nuclei with the magnet
is associated with production of faint radio signals.
The computer processes these signals to produce
an anatomical image. MRI is useful for brain
imaging because it images soft tissue better than
other methods such as computed tomography.1
Functional magnetic resonance imaging (fMRI)
is a relatively new application of MRI technology.
The purpose of fMRI is to map brain activity; thus it
is used to study brain function. In contrast, MRI
studies brain anatomy. Some authors talking about
fMRI distinguish it from MRI by referring to the latter
as structural MRI.
The principle behind fMRI is the fact that
increases in activity in a particular area of the brain
produce an increase in the blood flow to that area.
The magnetic properties of oxygenated blood differ
from those for deoxygenated blood, with these
properties changing linearly with blood oxygenation
over a broad range. The fMRI images are
constructed based on this effect, which is referred
to as the blood oxygen level-dependent (BOLD)
effect.2
During fMRI, a task is presented to the patient
or subject, and the brain area or areas active during
that task are mapped. The hemodynamic response
signal peaks about four to six seconds after neural
activity and does not return to baseline for 12 to 14
seconds. Therefore, the temporal resolution of
fMRI is limited. However, the spatial resolution is
good, with an ability to distinguish between areas of
brain activation only a few millimeters apart.2
Clinical Applications of fMRI
To date fMRI has had limited use as a clinical
diagnostic tool, the primary reason being that there
is insufficient standardization of testing and data
analysis procedures.3 An important use is
presurgical mapping to examine areas of normal
and disturbed brain function so that surgical
procedures can be planned. Because other
procedures for presurgical mapping are invasive,
fMRI offers a significant advantage.
Examining the effects of stroke or detecting a
stroke at an early stage may be another application
of fMRI. Because fMRI does not involve the use of
radiation as in other forms of neuroimaging, fMRI
has the potential of being used for longitudinal
follow-up of progressive or degenerative
neurological disorders, such as brain tumors or
Alzheimer’s disease. It may also be found to be
useful in monitoring the effects of therapeutic
approaches.
Persons preparing to undergo fMRI should be
aware that the strong magnetic field used in fMRI
will pull on ferromagnetic metallic objects in the
body, such as heart pacemakers, implanted ports,
infusion catheters, metal plates, or surgical
staples.4 Patients are asked to remove objects
such as hairpins, eyeglasses, jewelry, hearing aids,
and removable dental work. Patients recline on a
sliding table, with the head held still with a brace.
The patient then is asked to perform manual or
cognitive tasks in order to assess brain activity
during those tasks.
Examples of the Use of fMRI in the Study of Vision
Functional magnetic resonance imaging has
been extensively used in research examining a
variety of different neural functions. Its widest use
has been in cognitive neuroscience. Vision is one
of the areas studied with fMRI. Some examples of
the use of fMRI to study vision will now be
discussed. It has been used to investigate the
organization of the human visual cortex.5-7 The
retinotopic representation of the cortex
(correspondence of retinal areas to areas in the
cortex) has been mapped and a hierarchical
processing (from simple image elements to
complex images) within the cortex has been
described. Cortical locations and responses in
color perception, object recognition, depth
perception, and motion perception have been
studied. Effects of attention on visual cortical
responses have also been studied. It is interesting
to note that visual perception and visual imagery
seem to occupy common locations in the cortex.5
One of the ways that the visual deficits in
Functional Magnetic Resonance Imaging:Overview and Examples of its Use in theStudy of Visionby David A. Goss, O.D., Ph.D.
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dyslexia have been demonstrated is with fMRI.8,9
Dyslexic subjects were found to have differences in
the processing of motion stimuli in two studies.
Functional MRI has also been used to study
various aspects of the neural control of eye
movements.10 The cortical areas involved in eye
movements have been mapped. For example, the
area in the frontal cortex functioning in eye
movements (the frontal eye fields) is Broadmann
area 6. The area of the frontal eye fields activated
in pursuit eye movements is posterior to the part of
the frontal eye fields activated in saccades. Results
with fMRI also indicate that some neuronal
complexes for motion perception are shared in
common with pursuit eye movements.
Subcortical areas have also been studied with
fMRI. An example is the superior colliculus, located
on the roof of the brain stem.11 The retinotopic
organization of the superior colliculus was studied,
with the upper visual field being represented
medially and the lower visual field represented
laterally. The superior colliculus was also found to
be activated by moving stimuli.
Additional Resources for Information on fMRI
Since its initial development in the early 1990s,
there has been a great deal of research conducted
with fMRI. The results of this research have been
reported in a wide variety of clinical and research
journals. There is even a journal devoted to MRI,
the Journal of Magnetic Resonance Imaging. A
PubMed search yields thousands of journal articles
on fMRI. The articles discussed here on the use of
fMRI to study vision were found on PubMed by
limiting the search to literature reviews of studies on
fMRI and vision in humans published in English.
The papers cited here were selected from over 200
found on that limited search.
Information on fMRI can be found through a
variety of online sources. AccessScience, an online
subscription encyclopedia, has a nice summary of
how fMRI works and some experimental findings.12
Its authors suggest that fMRI will have even greater
impact on the study of brain function in the coming
years. Another online subscription encyclopedia,
Encyclopedia of Life Sciences, has several entries
relating to brain imaging with fMRI and other
neuroimaging technologies.
Medline Plus13 is a good free resource to
search for consumer health information. A search
for fMRI on Medline Plus leads to an informational
site from the Radiological Society of North
America.4 Medline Plus also lists numerous sites
for information on MRI.
A Google search on fMRI leads to several sites
with authoritative information on fMRI. For example,
the Functional MRI Research Center at Columbia
University has an informative webpage.14 It
explains what fMRI is, the methods and procedures
it entails, and its future roles in clinical care and
neuroscience research. A website from the
Department of Clinical Neurology at the University
of Oxford provides details on how fMRI allows
investigators to study brain function and discusses a
number of its research uses in neurology, cognition,
and perception.15
References
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