Perimetry, today and tomorrow

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<ul><li><p>Perimetry, today and tomorrow </p><p>J.M. ENOCH </p><p>School of Optometry University of California, Berkeley, Berkeley, CA 94720 and Department of Ophthalmology, University of California, San Francisco, San Francisco, CA 94143, USA </p><p>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. </p><p>Introduction </p><p>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 of all of our diagnostic and therapeutic techniques. Thus, this set of test methods should have growing emphasis in opthalmic practice. </p><p>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 of calibrating and specifying all sources of light, as well as the selection of rational settings for tests (Enoch, 1963; Aulhorn and Harms, 1972). </p><p>In the past decade, we have seen four resultant evolutionary processes. These are: the initiation of modem standardization of perimetry; the devel- opment Of first-stage automation 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 of testing visual function. I will </p><p>Read at the XXIVth International Congress of Ophthalmology, San Francisco, 31th October-5th November 1982 </p><p>307 </p><p>Documenta Ophthalmologica 55,307-322 (1983). 9 Dr W. Junk Publishers, The Hague. Printed in The Netherlands </p></li><li><p>3O8 </p><p>discuss each of these four developments in turn, and try to convey to this distinguished audience my concept of the state-of-the-art. </p><p>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. </p><p>Standard izat ion o f perimetry </p><p>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. </p><p>In fact, the situation we encountered was even worse, because available standards were in illuminance units, rather than luminance units; that is, the </p><p>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. </p><p>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). </p></li><li><p>309 </p><p>While further development of standards certainly is needed in many areas, a foundation for growth is now in place. </p><p>Automation of perimetric testing </p><p>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. </p><p>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. </p><p>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 </p></li><li><p>310 </p><p>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. </p><p>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 functions- 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. </p><p>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. </p><p>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. </p><p>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, </p></li><li><p>311 </p><p>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. </p><p>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. </p><p>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. </p><p>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. </p><p>I am not sure where to place the Decker/Balor device attached to the 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. </p><p>Localization of anomalies </p><p>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 </p></li><li><p>312 </p><p>requirement for senstivie procedures for use in the relativ...</p></li></ul>