Table of contents v

Table of contents

Perimetry Update 2002/03 contains a selection of papers presented at the 15th Visual Field Symposium of the International Perimetric Society (IPS) meeting held in Stratford upon Avon, England, from 26–30th June 2002. The meeting, titled ‘Perimetry and Imaging in Shakespeare’s Country’, was hosted by Professor John Wild of Cardiff University.

The meeting included the 2nd IPS lecture given by Professor Erik Greve, titled ‘I come to praise perimetry’ which led delegates through an entertaining history of the IPS from its conception and first symposium in Marseille, 1974, through to its future in an ever demanding health care environment.

This was the first IPS symposium to incorporate sessions on imaging. The research focus of many members of the Society is the detection and management of glaucoma and their research interests frequently incorporate both perimetry and imaging. It was, therefore, felt appropriate that the symposium should broaden its remit to cover imaging of the optic nerve head. Two of the 15 scientific sessions were devoted to this topic with papers covering new developments/findings with the Heidelberg Retinal Tomograph and the GDx Scanning Laser Polarimeter as well new ideas in the presentation and analysis of optic nerve head images.

The meeting had a further 13 scientific sessions devoted to perimetric research. These sessions covered a wide range of topics including new techniques, variability and basic science. Two sessions were devoted to variability, which has become a major topic for perimetric researchers. Contributors benefited from wide ranging discussions of their work both during the scientific sessions and the accompanying social events.

These proceeding will be available in digital format, along with all the other published proceedings, through the IPS web site: http://www.perimetry.org This site also contains much useful information about the Society with a comprehensive set of links to eye resources on the internet.

The editor wishes to thank all those involved in the production of this volume including the reviewers of the manuscripts whose comments helped to ensure the high quality of papers. Thanks are also given to Kugler Publications for their editorial support and to Patrice Henson for secretarial work. Finally, a very special thanks goes to John Wild for his organisation of the Stratford meeting and to Michael Wall and Richard Mills for their continued commitment to the Society.

The next IPS symposium is to be held in Barcelona from June 29th to July 2nd 2004 and the plans for that meeting are already well advanced with Dr. Francisco Javier Goñi acting as the host.

David Henson

Manchester, UK.

CUMULATIVE DEFECT (BEBIÉ) CURVES FOR FREQUENCYDOUBLING TECHNOLOGY PERIMETRY

CHRIS A. JOHNSON1 and PAUL G.D. SPRY2

1Discoveries in Sight Research Labs, Devers Eye Institute, Portland, OR, USA; 2Bristol Eye Hospital, Bristol, UK

Abstract

Purpose: Cumulative defect curves have been employed in conventional automated perimetry to permit the subjective classification of diffuse and localized visual field loss. The purpose of this investigation was to determine whether a similar procedure could be developed for frequency-doubling technology (FDT) perimetry. Methods: FDT results from 407 normal subjects between the ages of 18 and 85 years were used to construct cumulative defect (Bebié) curves. After adjusting for the effects of normal aging (normalizing to an ‘average’ 45-year-old), total deviation values (deviation from the average normal sensitivity) were determined for the 19 stimulus locations of the N-30 full threshold program. The total deviation values were then rank-ordered from the best (most plus, least minus) to worst (least plus, most minus) values and the fifth and 95th percentiles were determined. Results: FDT cumulative defect (Bebié) curves for FDT are remarkably similar in form to those derived for conventional automated perimetry. Clinical examples are presented to illustrate how these curves can be employed to characterize normal, diffuse, localized and mixed visual field properties for FDT. Discussion: Cumulative defect (Bebié) curves for FDT are a useful means of distinguishing diffuse from localized visual field loss.

Introduction

Frequency-doubling technology (FDT) perimetry is a new visual field test procedure that has been reported to be effective in detecting visual field loss in glaucoma, retinal disease and neuro-ophthalmological disorders.1-13 The commercial version of FDT perimetry (Welch Allyn, Skaneateles, NY, and Carl Zeiss Meditec, Dublin, CA) uses stimuli that consist of a 0.25 cycle per degree sinusoidal grating undergoing 25 Hz counterphase flicker. The low spatial frequency and high temporal frequency are responsible for generating the frequency-doubling effect, in which twice as many light and dark grating bars are perceived than are actually physically present. The C-20 program presents a central circular 5-degree diameter stimulus and 16 (four per quadrant) 10 × 10 degree square stimuli within the central 20 degrees radius of the visual field. The N-30 program adds two additional stimuli above and below the nasal hori-

Address for correspondence: Chris A. Johnson, PhD, Discoveries in Sight Research Labs, Devers Eye Institute, Legacy Clinical Research and Technology Center, 1225 NE Second Avenue, PO Box 3950, Portland, OR 97208-3950, USA. Email: cajohnso@discoveriesinsight.org

Perimetry Update 2002/2003, pp. 3–12

Proceedings of the XVth International Perimetric Society Meeting, Stratford-upon-Avon, England, June 26–29, 2002

edited by David B. Henson and Michael Wall

© 2004 Kugler Publications, The Hague, The Netherlands

4 C.A. Johnson and P.G.D. Spry

zontal midline between 20 and 30 degrees eccentricity for detecting nasal steps. FDT perimetry has a statistical analysis package similar to the Statpac program

available on the Humphrey perimeter.14 Characterization of diffuse and localized visual field loss can be achieved by the mean deviation (MD) and pattern standard deviation (PSD) visual field indices. The Viewfinder software package (Welch Allyn, Skaneateles, NY) permits additional characterization of diffuse and localized visual field loss by means of the total deviation and pattern deviation probability plots.

Another method for graphically characterizing visual field loss is the cumulative defect or Bebié curve, which has been found to be useful for standard automated perimetry because it provides a very rapid indication of the degree of diffuse and localized visual field loss.15-18 The cumulative defect curve is generated by determining the deviation of an individual’s sensitivity values from the age-adjusted average normal sensitivity values for each visual field location. These deviation values are then rank-ordered from highest to lowest and compared to the fifth and 95th percentiles for the normal population. The normal cumulative defect curve for standard automated perimetry appears to be slightly sigmoidal. If an individual has higher than normal sensitivity, results will be above the line indicating the upper normal limit. Similarly, less than normal sensitivity will fall below the line indicating the lower normal limit.

The purpose of the present investigation was to derive a normative database from which cumulative defect (Bebié) curves could be produced for FDT perimetry, and to determine whether they have clinical utility for distinguishing diffuse versus localized loss for FDT perimetry.

Methods

FDT perimetry results were obtained for 761 eyes of 407 normal observers between the ages of 18 and 85 years, as part of a previous multicenter normative data collection effort at the University of California, Davis, the University of California, Berkeley, the University of Iowa, and the Veterans Administration in Brooklyn.1 To be included in the investigation, both eyes of the subject were required to meet the following criteria: normal slit-lamp examination , normal ophthalmoscopic evaluation of the optic nerve and macula, best-corrected visual acuity of 20/40 or better, intraocular pressure of less than 20 mmHg, refractive errors of less than five diopters spherical equivalent and three diopters cylinder, and normal and reliable visual fields for the Humphrey Field Analyzer 30-2 full threshold test. In addition, subjects were excluded if they had diabetes or other systemic diseases, a prior history of ocular or neurological disease or surgery, a family history of glaucoma, or were taking medications that are known to affect visual function.

FDT perimetry was conducted using the N-30 full threshold program that is available on the commercial FDT perimeter (Humphrey Systems, Dublin, CA, and Welch Allyn, Skaneateles, NY). The full threshold procedure employs a modified binary search (MOBS) procedure19 to obtain threshold sensitivity estimates for each of the 19 visual field locations. The stimuli consist of sixteen 10 × 10 degree squares (four per quadrant), plus two additional squares above and below the horizontal midline between 20 and 30 degrees, and a central 5-degree diameter circular target. Within each

square, a 0.25 cycle per degree sinusoidal grating undergoing 25 Hz counterphase flicker is presented. The contrast of the target is varied according to the patient’s responses, decreasing contrast if the patient saw the stimulus, and increasing contrast if the patient did not see the stimulus. For each test location, testing terminates if there has been a minimum of four reversals in response (yes to no and vice versa) and the upper and lower response limits are within an acceptable range. Additional details of the MOBS procedure have been published previously.5,10,19 Testing time for the FDT N-30 procedure is typically five to six minutes per eye.

For each visual field test location, the effects of normal aging were determined. Although a linear function provided a good fit to the data, it was determined that a nonlinear fit provided a somewhat better fit to the data. The final form of the function was y = a + b*age +c*age2. This function produces a slightly steeper reduction in sensitivity for individuals older than 60 years. Details of the derivation of the normal aging correction have been provided in a prior publication.1 This function was used to adjust all normal values to a 45-year-old equivalent. Total deviation values were then determined for each individual by subtracting the average 45-year-old equivalent sensitivity values from their individual age-corrected sensitivity measure to derive total deviation values for each stimulus location. Total deviation values for each individual were then rank-ordered from highest (most plus or least minus) to lowest (least plus or most minus), the data were pooled and the fifth and 95th percentiles were determined to form the basis of the cumulative defect (Bebié) curve.

Results

Figure 1 presents an example of results from an individual whose FDT sensitivity values are within normal limits. The left panel presents the cumulative defect (Bebié) curve, with the dashed lines representing the fifth and 95th percentiles for the normal age-corrected total deviation values and the thick solid line representing the individual patient’s data. It can be observed that all the patient’s data fall within the normal fifth and 95th percentiles for all stimuli. The right panel shows the standard Viewfinder FDT printout for a right eye. It can be observed that all the numerical values, total and pattern deviation plots, visual field indices (MD and PSD) and reliability indices, are within normal limits.

Figure 2 presents an example of a glaucoma patient’s left eye that has predominantly diffuse loss. The cumulative defect (Bebié) curve in the left panel shows that the patient’s data fall below the normal limits, and that the deviation appears to be about the same along the entire curve. The right panel shows that the sensitivity values are low and are reasonably similar throughout the visual field. The total deviation plots show many locations that are outside normal limits. However, only a few locations on the pattern deviation plot are outside normal limits. Also, MD is outside normal limits, but PSD is not. All these are indicators of predominantly diffuse loss. Note how this can be immediately observed from the cumulative defect (Bebié) curve.

An example of predominantly localized loss is presented in Figure 3. In the left panel, the cumulative defect (Bebié) curve shows that the patient’s data are at the lower end of normal for the first portion of the curve, after which there is a steep drop for the remainder of the curve, which is created by the superior arcuate defect shown in the right panel.

A more subtle example of localized loss is shown in Figure 4, which presents an example of the right eye of a patient with a subtle nasal step. Most of the patient’s data on the cumulative defect (Bebié) curve are near the lower limit of normal, except that there is a steep drop for the last two locations on the curve. Finally, Figure 5 presents an example of combined diffuse and localized loss. The patient’s data fall below the normal limit throughout the length of the curve, but become progressively steeper from left to right, indicating the localized visual field loss.

Discussion

In this investigation, we have demonstrated that it is possible to develop and utilize a cumulative defect (Bebié) curve for FDT perimetry, based on a large normative database. The shape of the FDT cumulative defect (Bebié) curve is remarkably similar to the one that is available on the Octopus perimeter for evaluation of standard automated perimetry results. The FDT cumulative defect (Bebié) curve is a simple graphical representation of visual field data that can be rapidly examined to determine the degree of diffuse and localized visual field sensitivity loss that is present. Illustrative examples in this paper suggest that it can be a useful adjunct to existing FDT data analysis and graphical representation schemes, and that it may be a helpful tool for distinguishing between diffuse and localized loss for FDT perimetry.

Acknowledgments

We are grateful to Drs Mark Bullimore, Craig Adams, Murray Fingeret, and Michael Wall for kindly providing their normative data which had previously been collected as part of an investigation of normal aging effects for FDT perimetry.1

Supported in part by a National Eye Institute Research Grant # EY-03424 to CAJ. CAJ is a consultant for, and receives research support from, Welch Allyn (Skaneateles, NY), and receives research support from Humphrey Systems (Dublin, CA).

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