Perimetry, today and tomorrow

J.M. ENOCH

School of Optometry University of California, Berkeley, Berkeley, CA 94720 and Department of Ophthalmology, University of California, San Francisco, San Francisco, CA 94143, USA

Abstract, Perimetry is clearly in an explosive stage of development. Here, an attempt is made to bring together major developments and put them into an orderly perspective. The projection-bowl-perimeters of Bern and Ttibingen set the stage. Standardization provides the base for future development and data exchange. Automation and inclusion of computational procedures enhance the possibility of broad utilization for better screening and advanced testing. New test procedures make possible extremely fine localization of functions and allow superior definition of areas of involvement in path- ology. New fundus perimeters make possible instantaneous fine correlations between functional changes and observed retinal anatomic lesions.

Introduction

Perimetry provides, generally, rather simple techniques for evaluation of the functional status of the eyes. Finally, the functional integrity of the visual system is the goal o f all of our diagnostic and therapeutic techniques. Thus, this set of test methods should have growing emphasis in opthalmic practice.

I see perimetric studies undergoing explosive development at this time in a variety of ways. This development is built upon earlier contributions from a small number of laboratories in Genoa (by Maggiore), Bern (Goldmann, 1945; Fankhauser , and Schmidt ) TiJbingen (Aulhorn and Harms, 1956; Harms, 1940, 1954), Baltimore (Sloan, 1939), Paris (Dubois-Poulsen, 1952; Jayle, 1960), etc. which resulted in modern pr0jection-bowl-perimeters. These devices, which were largely developed in the late forties and in the fifties, provided us with a platform upon which to build. This includes the capability o f calibrating and specifying all sources o f light, as well as the selection of rational settings for tests (Enoch, 1963; Aulhorn and Harms, 1972).

In the past decade, we have seen four resultant evolutionary processes. These are: the initiation of modem standardization o f perimetry; the devel- opment Of first-stage automat ion both for screening and more generalized testing; the development of new tests better able to localize pathology along the visual pathways; and, more recently, the marriage of the fundus camera with the perimeter as well as other means o f testing visual function. I will

Read at the XXIVth International Congress of Ophthalmology, San Francisco, 31th October-5th November 1982

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Documenta Ophthalmologica 55,307-322 (1983). �9 Dr W. Junk Publishers, The Hague. Printed in The Netherlands

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discuss each of these four developments in turn, and try to convey to this distinguished audience my concept of the state-of-the-art.

In a sense, the development of modern perimetry had its origin in the laboratories of Tschermak in Prague, for both Goldmann (1945) and Harms (Harms, 1940, 1950, 1954; Aulhom and Harms, 1956) were students of Tschermak. Modern perimetry is largely built on the solid foundation of classical physiological optics that they and others received in Prague. It is clear to me that clinicians who conduct advanced visual field studies must have a profound understanding of the fundamentals of classical and current physio- logical optics and vision testing. Stated another way, our clinical capabilities today far outstrip the understanding of the fundamentals available among many of the practitioners utilizing the devices provided by manufacturers. This results in very real limitations relative to the utilization of such devices, and should be corrected as promptly as possible in our training efforts.

S t a n d a r d i z a t i o n o f perimetry

Projection-bowl-perimeters allow specification and calibration of all test parameters associated with perimetric judgments. Further, through use of static perimetric procedures, one could test a variety of visual functions at a given locus in the visual field. Although perimetric tests were designed to determine visual response to luminous stimuli, it is amazing that prior to the general development of projection-bowl units, specification of the stimulus was rarely controlled. The fundamental purpose of standardization is to pro- vide a common framework for measurement and, hence, for exchange and comparison of data. If each person conducts a test differently, comparison of results between clinics or offices becomes extremely difficult. Without appropriate specification of test conditions, fine or subtle tests cannot be compared.

In fact, the situation we encountered was even worse, because available standards were in illuminance units, rather than luminance units; that is, the

�9 amount of light falling on a surface or a test target was specified, rather than light reaching the eye (Int. Standard on Perimetry, 1929). Thus, there was no distinction made between stimuli falling on black, white, grey, or chromatic surfaces.

Action was initiated by the U.S. National Academy of Sciences - National Research Council Committee on Vision. Working with representatives of ophthalmology, optometry and supportive basic sciences, a 'First Inter- professional Standard for Visual Field Testing' was developed in 1975 (Comm. on Vision, 1975). This document served as a spur to further development of a more advanced international standard by the International Perimetric Society which was approved at the last Congress in Japan in 1978 by the Concilium Ophthalmologicum Universale (1979). This document was reaffirmed at the recent International Perimetric Society meeting just held in Sacramento (1982).

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While further development of standards certainly is needed in many areas, a foundation for growth is now in place.

Automation of perimetric testing

Perimetry is relatively time-consuming; there is a need for enhanced uniformity in testing procedures; there are few really well-trained perimetrists available; and there are few training programs for perimetrists (either for clinicians or technicians). This area of our technical expertise was, therefore, fertile ground for development of automated techniques (Koch et al., 1972; Fankhauser et al., 1972, Fankhauser, 1978; Fankhauser and Bebie, 1979; Spahr et al., 1978; Haberlin et al., 1980; Bebie and Fankhauser, 1981; Gloor et al., 1981). First, however, it was necessary to define what it is that the perimetrist does and how to optimize the quality of the test including detection of lesions and measurement of visual deficits. In this development, in many instruments, major attention has been paid to glaucoma detection (Rock et al., 1971, 1973) rather than to the broad range of other perimetric uses, i.e., neuroophthahnologic, geriatric, macular area function testing, driver or transport vision screening (Keltner and Johnson, 1980), ergophthalmo- logical applications, etc.

At the outset, it should be stated that through automation one gains common presentation of stimuli under uniform test conditions. There is possibility of mass screening, and much more; but there are also losses. Those who have mastered perimetric technique will know what I mean when I state that there is a special interaction between the patient and the examiner which allows detailed/fine investigation of lesions. The examiner can change course in the middle of his exam to pursue some worthwhile goal. There is also knowledge as to when some key part of the exam needs to be repeated; whether the patient requires a rest; and realization when the procedure should be aborted. In short, this is still only partly a science and partly an art. To the extent it is a science, we need largely to thank Fankhauser et al. (Koch et al., 1972; Fankhauser et al., 1972; Fankhauser, 1978; Fankhauser and Bebie, 1979; Spahr et al., 1978; Haberlin et al., 1980; Bebie and Fankhauser, 1981; Gloor et al., 1981). They have asked the critical questions; such as, how many points need to be tested per field area for a given probability of detection of a lesion of a given size and depth etc. At the same time, we should not overlook contributions by Keltner and Johnson (1980), Greve (1973), Hart (1981, 1982), Frisen (1979), Heijl (1977), and several other fine perimetrists.

As noted, we need automation because often the clinician has not the time to perform the examination and it is hard to train and retain a highly skilled perimetric technician. However, we must ask, what do we want the technician to do? Do we want that individual to merely seat the patient at the equip- ment, center the individual, change the record, put the visual correction in place, provide initial instructions, start the device, and obtain the record at the end? Additionally, do we want this person to monitor fixation, assure

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patient compliance, make judgements as to secondary field tests which need to be conducted, etc.? Do we require enhanced computer operator skills of the technician in place of perimetric skills? In short, the technician is not replaced, but rather the roles and educational requirements are altered. Selection of equipment and technicians needs to be matched with the needs of the individual office.

When one purchases a unit, numerous questions must be asked. For example, how finely is fixation monitored by the device; is exposure duration such that multiple eye movements are possible during an exposure; what is the false alarm rate and the failure rate; is the device simple to operate; is there suitable back-up service for the instrument; is the instrument capable of upgrading in a rapidly evolving field; does the clinician want to program the instrument himself or is he/she satisfied to use only the programs supplied by the manufacturer? In the case of the larger units, computational units are of such size that they can handle added computer functions in the office (accounting, recordkeeping, word processing, etc.). Is this a desired feature for the purchaser? Does the individual seek a screening device or one which offers a wide range of perimetric examination possibilities? Actually, units available range from simple screening funct ions- mainly for glaucomatous changes in the central field (Rock et al., 1971, 1973) up to devices conducting rather sophisticated analyses of the visual field. Most devices, with few ex- ceptions (such as the Perimetron manufactured by Coherent) utilize static rather kinetic perimetry.

The computer has difficulty drawing isopters through sets of points. There is no problem if the group of points are circular or slowly undulating. The problem arises where there are sharp alterations in isopter boundaries, deep scotomas, or multiple islands as opposed to a residual isthmus. The isopters tested in automated kinetic perimetry generally are radial relative to fixation, although it is possible to program a computer to track a line perpendicular to a second line connecting any two points.

Because of this set of problems, there has been a search for improved display formats that do not require point linkage in the form ofisopters. The Octopus group has come up with some imaginative formats for display of data (Fankhauser and Bebie, 1979; Gloor et al., 1981; Haberlin et al., 1980; International Standard on Perimetry, 1929; Spahr et al., 1978) as has William Hart, Jr. at Washington University in St. Louis (1981, 1982) but there is certainly no simply agreed upon format for presentation of data between manufacturers.

When performing static perimetry using an automated perimeter in a screening mode, it is generally desirable to use suprathreshold testing, particularly for screening; i.e., to present targets that the normal observer can see with some degree of confidence (Johnson et al., 1979; Keltner et al., 1979, 1981). If this is not done, one records too many false positives. That is, if for some reason general sensitivity or illumination is somewhat reduced,

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too many points are missed. If the background is not bright enough, this problem is exacerbated by a small or miotic pupil, an old bulb, or a dirty screen surface. Some devices make a preliminary set of measurements to determine how bright to set the remaining test points. This is a useful design feature.

As noted, available instruments range from rather simple screening devices on up to major diagnostic/computational units. Simpler screeners are the Automated Tangent Screen and the Coherent Ocuplot. Here the screening is largely for glaucoma and is based (as are most other devices) on the static only portion of the Armaly-Drance glaucoma screening test regime (Rock et al., 1971, 1973). More advanced instruments have greater numbers of test points, and they provide a variety of suprathreshold screening tests including glaucoma, neurological (test points located on both sides of the vertical mer- idian), and central field tests (often a modification of the blind spot test point array with shifted fixation). This group includes the Cavitron Biomed Unit, the Synemed Fieldmaster, and the Dicon. It is obvious that the Cavitron and the Synemed Units had common ancestry, but that the Synemed has further developed their more advanced units. Dicon, a new-comer in this competitive market, has several rather imaginative new features. The Fieldmaster and the Dicon can perform static perimetric testing at given points in the visual field.

I cannot claim familiarity with several of the European computers, including the Rodenstock Peritest, the new Aulhorn-Oculus Unit, the Swedish Competer, or the developmental units in Italy.

The more ambitious units in terms of program variations, more complete testing capabilities are the Coherent Perimetron (a kinetic test unit), the Synemed Squid, and the Octopus. The latter unit, the Octopus, is clearly the Rolls Royce of the field. Synemed is rapidly developing their Squid instrument to compete with the Octopus manufactured by Interzeag - who in turn has developed a somewhat reduced model to compete with the Squid. I believe the Rodenstock Peritest and the Aulhorn-Oculus are meant to be placed in this group.

I am not sure where to place the Decker/Balor device attached to t h e Goldmann Haag-Streit Perimeter, nor the Friedman Field Analyser units in the above list. The list is long and growing. When purchasing, one must select with care the unit which best serves the practitioner's needs after careful comparison of features offered.

Localization of anomalies

The early flowering of perimetry reflected the fine localization capabilities of visual field testing, particularly as it pertained to chiasmal and certain other central lesions and the characteristic nerve fiber bundle anomalies commonly seen in glaucoma. These conditions were readily diagnosed using kinetic perimetry. Pressure for repeated evaluations at a single point in the field, the

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requirement for senstivie procedures for use in the relatively flat 'plateau' portion of the visual field, and the need for early and reliable detection of glaucomatous field defects led to the development of static perimetry, a form of quantitative, point-by-point perimetry. These techniques helped clarify the course of disease processes in a far superior manner (Aulhorn and Harms, 1972; Enoch, 1963; Gloor et al., 1981).

The scientist, seeking to define localizing psychophysical tests or simply tests of vision, has many choices in the current literature. When approaching the subject, questions relative to the general adaptability of the test procedure to the clinical environment take precedence: such as, what is the magnitude of the effect measured; is there difficulty in calibrating the necessary apparatus; is the measured function relatively exclusive compared to other tests; and, of course, what is the difficulty of the task for the patient?

This has been a topic of special interest in my laboratory for many years (Enoch, 1978; Enoch and Campos, 1978, 1980; Enoch and Sunga, 1969; Enoch et al. 1970, 1976, 1979, 1980; Fitzgerald et al., 1981; Proenza et at., 1981; Sunga and Enoch, 1970; Temme et al., 1980). The following battery of tests largely defines the available localizing series of tests we use or have used:

Retinal receptor level

(a) Fundus reflectrometry; i.e., measurement of the bleaching properties of the photosensitive pigments (Enoch, 1970; Proenza et al., 1981; Ripps, 1976; Ripps et al., 1978).

(b)The Stiles-Crawford function; i.e., the assessment of the alignment (orientation) of the retinal receptors. Coincident with these measures, general sensitivity is often sampled as well as the increment threshold curve (Enoch and Tobey, 1980).

lnner retinal layers

(a) The sensitization-desensitization function of Westheimer (also operationally defined as the sustained-like function by this author). This test, probably biased by receptive field properties of the inner retina, is affected by pathology of the inner and/or outer plexiform layers. It is a test of spatial summation (Enoch, 1978; Enoch et al., 1980; Enoch and Campos, 1980; Proenza et al., 1981).

(b)The transient-like function, based on the rotating and non-rotating windmill target of Werblin, is affected by pathology affecting the inner plexiform layer. It, too, is a form of spatial summation test (Enoch, 1978; Enoch et al., 1980; Enoch and Campos, 1980; Proenza et al., 1981).

Tests o f the optic pathways central to the optic nerve head

(a) The flashing repeat static test (FRST). This is simply a repetitive test of the static perimetric threshold from non-seeing to just detection using a flashing or pulsed stimulus. Anomalies and disease processes affecting the

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optic nerve and central loci, such as in multiple sclerosis, optic neuropathy in its many forms, etc., cause a measured loss in sensitivity in just a few minutes. One assumes that this is a test of the white matter tracts. The effect is a form of visual saturation or fatigue (Enoch, 1978; Enoch et al., 1980; Campos and Enoch, 1980; Proenza et al., 1981).

(b) Troxler's effect. Stabilized retinal images fade in time. Rarely, in central visual pathway lesions, there is an accelerated fading of stimuli which are not flashed at given loci in the visual field (Enoch and Sunga, 1969; Sunga and Enoch, 1970).

Test of central function

(a) Hyperacuity test designs. Included in this group are tests of vernier acuity, detection of line tilt, stereopsis, etc. Evidence is accumulating that these responses are organized centrally. This test is new to our test battery (Enoch and Williams, 1983).

Many other tests could be added to this group to aid further in localization. These include dark adaptation (Ripps, 1976; Ripps et al., 1978), glare recov- ery, optokinetic nystagmus and contrast sensitivity functions. Further, electro- diagnostic tests provide valuable added information; such as, the retina wide, patterned and local ERG, EOG, and VER (or VEP) (Awaya, 1972; Berson, 1981; Inatomi, 1977, 1979; Meyers, 1959; Regan and Murray, 1978; Regan et al., 1976, 1977; Ripps, 1976; Ripps et al., 1978; Sandberg et al., 1977, 1978, 1979; Trantas, 1955). Tests of pupillary response can aid in localization of anomalies.

In addition to the quantitative point-by-point perimetry made possible by static perimetry, these tests now make possible quantitative layer-by-layer assessment performed at designated points in the visual field (Enoch, 1978; Enoch et al., 1980; Enoch and Campos, 1980; Proenza et al., 1981). Analysis, degree-by-degree, across a lesion is now possible.

For those less familiar with such tests, one always needs to emphasize that the judgement, 'I see a light', implies functional participation of a substantial portion of the visual system (Enoch, 1978; Enoch et al., 1980). Tests of localization represent biases of response. That is, one designs a test to empha- size the response properties of a local response unit, e.g., there are groups of amacrine cells which are particularly sensitive to onset and offset events, i.e., transients. In the human, retinal neurons tend to have circular receptive fields, etc. Thus, windmill shaped targets, rotating at an optimal speed and of the appropriate size, might be expected to drive the associated amacrine cells to near maximum response (Enoch, 1978; Enoch et al., 1976, 1980; Enoch and Campos, 1980; Proenza et al., 1981). To be sure that the test is weighted towards the desired bias, one must examine a large population of individuals who exhibit selected pathology assignable to known sites of origin. Questions of upstream and downstream effects of pathology have to be addressed as well as the influence of one response unit or function on other measured functions (Enoch and Williams, 1983). Pathology which is altering state; i.e.,

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either exacerbating or remitting, is particularly useful in defining critical relationships (Proenza et al., 1981).

Other major laboratories are seeking to develop localizing tests as well. These include Berson and his group (Berson, 1981; Proenza et al., 1981; Sandberg et al., 1977, 1978, 1979) at the Berman-Gund Laboratory at Harvard University; Ripps (1976, Ripps et al., 1978; Proenza et al., 1981) Siegal and Carr at New York University; Regan (Regan et al., 1976, 1977; Regan and Murray, 1978; Proenza et al., 1981) at Dalhousie University; and Pokorney and Pokorney (Proenza et al., 1981) at The University of Chicago. A recent symposium report provides broad perspectives relative to the current status of such research (Proenza et al., 1981). Many of these techniques are now ready for much broader utilization.

It is important to emphasize that no one of us claims our individual tests represent the unique solution to the localization of function. Rather, these initial efforts have proved successful and hence are worthy of further elabor- ation and study. Since invasive studies of the human are generally not possible, nor ethically desirable, these methods also help us understand the intrinsic nature of human visual response. Here, pathology of known origin acts as a natural dissector for purposes of investigation.

One of the problems encountered today is the diversity of backgrounds of many young investigators and clinicians. Those trained in the basic sciences, who have the necessary knowledge of modern psychophysical and electro- physiological techniques, often just do not appreciate the clinical environment nor the problems generally encountered by the clinician. This has been termed the 'interface problem'. One of the reasons the Association for Research in Vision and Ophthalmology was developed was to address this problem. It has been only partially successful in meeting this challenge.

The problem is profound (Enoch and Williams, 1983). Those in the more basic sciences are generally hesitant to surrender their elaborate controls, multiple trials and orderly procedures for the (in their eyes) seeming disorder of the clinic. They generally do not appreciate the real limitations in time available to the clinician, or the often limited period during which the patient is available for study, or the various ways in which pathology may be ex- pressed, and/or the multitude of procedures which must be performed in the limited time frame available. If one approach is not proving successful or practical, the need for alternative procedures is also not appreciated. Nor finally, do the basic scientists realize that the clinician is making judgements on the totality of his/her examination, the case history, and his/her per- ceptions - not on one test or another taken in isolation. The fact that most of the testing is conducted, so to speak, before the patient ever arrives in the clinic is generally overlooked; i.e., the data of the patient are compared to predetermined matched population norms.

In an effort to begin to breach the dichotomy in perceptions between basic and clinical scientists, Enoch and Williams (1983) recently developed an orderly statement defining how one translates a promising basic test into a

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useful clinical routine. Refinement of such approaches could contribute a great deal to breaking down the interface problem. This development needs to be coupled with special training programs designed specifically for basic scientists seeking to apply their knowledge, and for clinicians seeking to broaden their clinical armamentarium.

The fundus perimeter

The major new development in perimetry is the combining of the perimeter and fundus camera. The idea is basically very simple. In the fundus camera, we can introduce a fixation point visible both to the patient and to the camera. If this can be done, stimuli of other sorts can be introduced, and response can be recorded at specific chosen points on the displayed retinal image. The infrared fundus camera provided an early boon to this develop- ment because the clinician could view the retina while conducting perimetry without meaningfully altering the light adaptation of the patient.

Trantas in 1955 first described an early form of this technique followed by Meyers in 1957. More recently, activity was spurred by a paper by Awaya in 1972. Others, all Japanese, participated in early development (Inatomi, 1977; 1979; Isayama and Tagami, 1977; Kani and Ogita, 1979; Kani et al., 1977; Ohta et al., 1979, 1981). Kani and Ohta and their co-workers are among the leaders in this area of endeavor. Three developmental units were demonstrated at the International Perimetric Society meeting in Tokyo in 1978. Canon had a functioning prototype commercial instrument.

Since the 1978 international meeting, there has literally been a flowering of activity in this area of endeavor all over the world. In part, this has been accompanied by the explosion in data processing capability and new electronic and electro-optic technologies. Canon konan displayed commercial instru- ments at the International Ophthalmological Congress in San Francisco (1982). Others are clearly at Work. Nothing prevents the development of apparatus allowing an interactive relationship between the clinician and the display; i.e., ~ the clinician might well wonder about the functional integrity of some detail near an arterio-venous crossing, and he/she could specify what test or tests he/she wants to conduct, either fundus reflectometry, psychophysical tests, or some form of local electrophysiological examination. The clinician could then set equipment to perform that (those) test(s) and touch the screen where he/she would like the test(s) to be performed. Depending on the hardware/software package, the-instrument could lock onto the display for purposes of image stabilization and conduct the desired tests. Other analytic devices can measure local blood flow and oxygenation. Nothing prevents near complete automation of these procedures as well. The potential power of such test devices must be obvious to the reader. The fact is that all aspects of the above are under active development at this time!

With over one-third of the attendees of the last International Perimetric

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Society meeting in Bristol (1980) from Japan, I am looking forward to the contributions of this group in the future.

In the United States, several groups are active in research and development of fundus perimetry. These include the Retina Foundation Group in Boston including Schepens, Hirose, Trempe, Mainster, Pomerantzeff, Webb, Timber- lake andHughes(Mainster et al., 1982; Webb et al., 1980; Webb and Hughes, 1981; Timberlake et al., 1982). They have developed a number of scanning laser ophthalmoscopes for analysis and testing of fundus images. Those images can be stabilized using a Stanford Research Institute Eye Tracker device (and can be used for fine laser treatment through image stabilization as well). The patient's retina can be analyzed for blood chemistry, or utilized for visual testing by psychophysics or electrophysiology. Hirose and Pomerantzeff have linked a wide-angle, fundus camera to tests of the local ERG and VER. Berson and Sandberg's local ERG device at Harvard could easily be incorporated (Berson, 1981; Sandberg et al., 1977, 1978, 1979).

At New York University, the Ripps, Carr, and Siegel group (Proenza et al., 1981; Ripps, 1976; Ripps et al., 1978) is modifying a fundus camera device to provide point by point analysis of photosensitive pigments on the retina by fundus reflectometry.

Ernest, Fishman, Fram, Read, and McCormick (Fram et al., 1982) at the Illinois Eye and Ear Infirmary will further develop an already-fine analytic opthalmoscope available there for suitable testing. They, too, have fundus reflectometry capability as well as capability for local chromatic analysis of the retina.

Enoch, Williams and Essock at Berkeley will be adapting their quantitative layer-by-layer and point-by-point perimetric techniques to fundus/perimetric devices (Enoch, 1977; Enoch et al., 1980; Proenza et al., 1981; Enoch and Campos, 1980; Enoch and Williams, 1983) Adams will be introducing his tests of the blue system as well.

At the ARVO meetings in Sarasota, it became evident that imaginative and active development of fundus perimetric equipment is being conducted by Bille and Klingbeil at Heidelberg in West Germany (1982).

The future

In this area as well as in so many endeavors in our society, we are programming our test devices with the solutions of the past. Very rarely do we look at our devices and ask what they are capable of performing, per se. In too few instances are we seeking to wed modern knowledge of visual function to the enormous capabilitie's inherent in electronic, optical and computational devices readily available to us.

In fact, we even see manufacturers program the weaknesses of the past. On the Haag-Streit Perimeter, given the mechanics of the static perimetric attachment, it is easiest to conduct a static perimetric survey along a given meridian through the point of fixation (or in a circular pattern). Some years ago, Matt Newman and Franz Fankhauser made a simple device which made if

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possible to take linear static cuts between any two points in the visual field on the Haag-Streit Perimeter. This device never caught on. Many manufacturers of automated perimeters still run all of their static cuts through the fovea. Why? Their equipment is certainly not limited, nor need that equipment be limited, in this manner!

One of the special properties of the computer which has been exploited only to a minor degree is its tremendous potential for storage of data, or as a data base resource. Early on, Lynn (Tate and Lynn, 1977) argued that there should be a national data repository which received input from a large sampling of offices about the United States. His plans, drawn in cooperation with the International Business Machine Corporation, never came to fruitation. The Octopus and the Squid instruments (and possibly one or two of the other larger instruments) have large enough computer memories for modest storage of data. This offers special analytic opportunities, because patients with the same anomalies can be compared and followed in time. Of great importance is the fact that records on the same patient can be compared in a quantitative manner on successive visits. If equipment exists, and there is a modem (telephone link) to a central computer storage facility, records on the same individual can be readily called up from any location at modest cost.

The Octopus Delta program, developed by Fankhauser et al. (Gloor et al., 1981) provides a readout of differences in a patient record between current and prior visits. It wisely considers magnitude of errors in making com- parisons. Another individual utilizing computer storage capacity and comparative analysis of records is William Hart at Washington University in St. Louis (Hart and Hartz, 1981, 1982).

Oddly enough, video display terminals have not yet really been used effectively in a mass screening mode. In most advanced societies, there is a television set available in the home or in some public place of gathering. The problem of test distance for mass screening can be resolved by using some multiple of the diagonal across the TV set as the test distance. Presbyopia or poor visual correction can be dealt with by using not too small test stimuli. Presentations would have to be made suprathreshold and as multiple presen. rations (for economic reasons) as in the case of the earlier Harrington-Flocks or Roberts screening devices. Patients exhibiting extinction phenomena Will show up as positives. Yes, there is a problem of contrast, picture quality, noise, the need for repetition of the test battery for each eye and multiple viewers. But the possible public health advantages relative to detection of anomalies are such that this form of endeavor should not be overlooked. Second stage referral screening centers might be needed. To my knowledge, only Flocks has made a serious effort to develop TV screening programs (Flocks et al., 1978). Modest suitable trials in schools, homes for the aged, driver testing (Keltner and Johnson, 1980), industrial settings, etc., are encouraged.

When talking to sales people at equipment shows these days, one hears much about the 'menu' offered by specific automated equipment. This refers

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to the programmatic options, i.e., glaucoma screening, neurological exam, blind spot exam, sector or special field exam, static perimetry, etc. In a sense it is a shame that manufacturers seem to be afraid to move away from simply testing static perimetric functions. There is just so much more available! At some point in time, this transition will be made. Then we will see a combining of current approaches, improved localization tests, new forms of testing*, and fundus perimetry. Presumably, enhanced utilization through improved training will be needed for this to occur.

One area where we have seen inadequate development is in testing of the visual field in infants and young children. Obviously, this is not easy. The use of objective determinations would be advantageous; e.g. measures of the local ERG and VER under ophthalmoscopic or fundus c a m e r a - perimeter control. Another option might be to hold fixation with some form of animation at the center of a screen exhibiting random dot patterns. Period- ically, targets could be presented in stereo display and correlograms (a form of EEG) might be plotted (Petrig et al., 1981). Such binocular responses may be recorded starting about three months of age.

During my first term on the National Advisory Eye Council, a grant application was submitted by a young scientist, I believe from Massachusetts, which offered an interesting possibility (I am afraid I forget the individual's name). The child would gaze monocularly (or binocularly) into a perimetric bowl with his/her eye movements monitored. The instantaneous locus of fixation can be computationally determined, a stimulus can then be flashed at a known locus in the projection bowl relative to his/her instantaneous point of fixation, and the child's response recorded. If the child looks toward the projected stimulus within a defined error zone area and within a fixed period of time, the child would be credited with a positive response.

In conclusion, this is a time of explosive growth and development. Import- ant and amazingly rapid progress is being made separately in standardization, automation, localization of lesions, and direct observation of lesions and functional response (fundus perimetry). There is a surprising lack of effort being made to tie these developments together. Further, except for some modest studies, very little thought has been given to optimally using new technology available to us at this time. While it may be quite unfair to say we are still programming the perimetrists' elbow or wrist (with some modest exceptions), the comment is not too far off the mark. Certainly, in the future we can expect further development and new initiatives in computer utilization, Some of which are suggested above.

*One new test format is the determination of interference acuity or resolution in the periphery of the field. This work is being Conducted in Iowa by Phelps et al. Many other options exist.

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Berson EL (1981) Electrical phenomena in the retina. Chapt 17 In: Moses RA (ed) Adler's Physiology of the Eye, Clinical Applications. St Louis, Mosby

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This work was supported in part by NEI Grants No. EY03674 and EY03669, NIH; Bethesda, Maryland.