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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.

References

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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

for hyperpolarizing neurons in shaping the b-wave. Vis

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VEPs in man. Vis Res 1987; 26: 165–177.

30. Sutter EE, Tran D. The field topography of ERG

components in man--I. The photopic luminance

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.


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


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.


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.


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

1. Charman WN. Imaging in the 21st century. Ophthal

Physiol Opt 1998;18:210-223.

2. DiGirolamo GJ, Clegg BA. Brain imaging: observing

ongoing neural activity. Encyclopedia of Life Sciences, John

Wiley & Sons, http://www.els.net, article online posting date

July 22, 2003.

3. Jezzard P, Buxton RB. The clinical potential of functional

magnetic resonance imaging. J Magnetic Resonance

Imaging 2006;23:787-793.

4. Radiological Society of North America. Functional MR

Imaging (fMRI) – Brain,

http://radiologyinfo.org/en/info.cfm?pg=fmribrain&bhcp=1,

2006, accessed July 6, 2006.

5. McFadzean RM, Condon BC, Barr DB. Functional

magnetic resonance imaging in the visual system. J Neuro-

ophthalmol 1999;19:186-200.

6. Wandell BA. Computational neuroimaging of human

visual cortex. Annu Rev Neurosci 1999;22:145-173.

7. Grill-Spector K, Malach R. The human visual cortex. Annu

Rev Neurosci 2004;27:649-677.

8. Eden GF, VanMeter JW, Rumsey JM, Zeffiro TA. The

visual deficit theory of developmental dyslexia. Neuroimage

1996;4:S108-S117.

9. Habib M. The neurological basis of developmental

dyslexia: an overview and working hypothesis. Brain

2000;123:2373-2399.

10. Dieterich M. Ocular motor system: anatomy and

functional magnetic resonance imaging. Neuroimaging Clin

N Am 2001;11:251-261.

11. Schneider KA, Kastner S. Visual responses of the

human superior colliculus: A high-resolution functional

magnetic resonance imaging study. J Neurophysiol

2005;94:2491-2503.

12. Stark CEL, Squire LR. Functional magnetic resonance

imaging (fMRI). AccessScience, McGraw-Hill,

http://www.accessscience.com, last modified April 30, 2002.

13. http://medlineplus.gov.

14. Columbia University Functional MRI Research Center.

About functional MRI (general): the future role of functional

MRI in medical applications, http://www.fmri.org/fmri.htm,

accessed July 6, 2006.

15. Parry A, Matthews PM. Functional magnetic resonance

imaging: a “window” into the brain,

http://www.fmrib.ox.ac.uk/fmri_intro/fmri_intro.php, 2002,

accessed July 6, 2006.

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