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A Review of Strategies for Screening of the Visual Fields
Abstract
Some strategies for rapid investigation of the visual fields are reviewed. Those aspects considered are the testing of central and peripheral fields, the pattern and density of sampling the visual field with static stimuli and the most suitable stimulus intensity at which to begin the screening of each subject. Some of the design features of 10 visual field screeners and 3 automated perimeters are tabulated to indicate the importance of control of perimetric variables and how strategies for screening have developed from earlier to later designs.
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The most serious disturbance in visual function is primarily deterioration of central visual acuity, followed by visual field changes. Furthermore, it is also important to detect visual field changes for diagnostic and therapeutic purposes.
The authors noticed while measuring the VF with Friedmann Visual Field Analyser (F.V.F.A.) in normal subjects the frequent occurence that a single stimulus point’s sensitivity was decreased as compared to remaining stimulus points. In order to clarify this, the visual fields of 592 eyes measured with the FVFA were analyzed and the positions with reduced sensitivity noted (fig. 1 and table 1).
Furthermore the authors have studied fundus photographs (within 30 degrees from fovea) and superimposed a chart of F.V.F.A. over the photograph, to see which point corresponded to a retinal vessel. They also compared the results of F.V.F.A. and Tübinger perimeter.
A number of studies on the frequency distribution of early visual field defects in glaucoma have been carried out using different methods of perimetry. All workers agree that the earliest defects occur within the Bjerrum area, 5°–15° eccentricity (1–5). Controversy lies as to whether early temporal paracentral scotomas connected to the blind spot can occur as an early field defect in glaucoma.
In doing perimetry, we aim for the earliest and most effective detection of visual field defects (9); with the introduction of new and standardized instruments, accuracy in the detection of visual field defects has increased.
A more elaborate description of this instrument has been given in Documenta Ophthal-mologica Proceedings Series,Vol. 22, pp. 71–74 (1980).
This perimeter (Fig. 1) has been constructed for automatic and non-automatic detection of visual field defects. Some technical data are presented in the table. The stimulus distribution is shown in Fig. 2.
The Peritest aims at completing a detectionphase within five minutes. At missed positions the intensity of defects can be further examined.
The method of screening for glaucomatous visual field defects proposed by Armaly was evaluated in 106 normal people and 49 people with glaucomatous defects. The method was found to have a high sensitivity and also a high specificity and with the modifications to be described, lends itself to clinical and survey screening. The method's strength and weaknesses are outlined in detail in the paper.
This third edition of the Diagnosis and Therapy of the Glaucomas by Kolker and Hetherington is recommended to students and practitioners of ophthalmology.
The basic format and most of the content of the previous edition have been wisely maintained by the current authors. Significant editions to the text have been made only in areas that have been developed since the last revision in 1965, which attests to the initial attention to careful organization and detail made by Drs. Becker and Shaffer. There are, however, small changes in organization throughout the text that reveal the authors' critical review of the previous writers' viewpoint.
The clinical importance of disc and field changes have been stressed with the addition of fluorescein angiography studies of the disc as well as refinements of static and kinetic perimetry with the Goldmann perimeter. Cup-disc diameter ratios and the ocular effects of corticosteroids have received their deserved expansion.
Multiple stimulus visual field examination can be used as a comparatively rapid method for the detection of visual field defects. However, the method should be correctly used and results should be sensibly interpreted. Based on a statistical analysis of the differential threshold values of 22 normal eyes of 22 normal subjects, it was concluded that (1) for accurate visual field examination, the application of a standard luminance of the stimuli for patients of a certain age group for the investigation of the visual field with multiple stimulus campimetry instruments should not be considered; it is preferable to perform threshold measurements as in single stimulus static perimetry; (2) simultaneous perception of differently localised stimuli, i.e. perception after an equal number of increments in luminance, is usually not possible due to the large variations in the shape of the individual sensitivity curves with respect to the average sensitivity curve. Consequently, simultaneousness of perception should not be considered as a criterion of normality; (3) multiple stimulus presentation merely facilitates simultaneous approach of the threshold level.
The visual fields of 1834 subjects with supposedly normal eyes were examined during a mass screening program with the Visual Field Analyser. All defects were checked by means of static and kinetic perimetry. Visual field defects were encountered in almost 2% of the subjects. It was shown that reliable mass visual field examinations can very well be carried out in a relatively short time (6 min per two eyes). The expenses are low and there are few false positive results (about 1).Die Gesichtsfelder von 1834 Personen mit angeblich normalen Augen wurden whrend einer Massen-Rntgendurchleuchtung untersucht. Alle Defekte erfuhren eine Kontrolle mit statischer und kinetischer Perimetrie. Gesichtsfeldausflle wurden bei beinahe 2% der untersuchten Personen angetroffen. Es erwies sich, da eine verlliche Gesichtsfelduntersuchung sehr gut in relativ kurzer Zeit auszufhren ist (6 min fr zwei Augen). Die Kosten fallen gering aus, und es gibt wenige falsch positive Resultate ( 1).
The Armaly technique, a method of screening for glaucomatous field defects was evaluated in 100 normal eyes and 38 selected central field defects using the Goldmann perimeter and the Auto-Plot tangent screen. The screening results obtained from the Goldmann perimeter and the tangent screen using the selective perimetry of Armaly were compared with the results obtained from the Friedmann central field analyser. Testing normal eyes we found the highest initial false positive rate with the Friedmann analyser and the lowest initial false positive rate with the Auto-Plot tangent screen. The specificity of the Friedmann analyser for detecting early central field changes is less than the Goldmann perimeter or the Auto-Plot tangent screen when using Armaly's technique. On the other hand, the Friedmann analyser turned out to be the easiest instrument to handle and requires least experiences for the observer. Some problems of mass screening perimetry are discusssd.
An apparatus for static perimetry of the central visual field at 64 points is described. The testing is fully automatic: the test logic is programmed into a mini-computer and the results are plotted as a diagram in polar coordinates.
A few cases with small or medium sized visual field defects have been analyzed by conventional methods and by the automatic instrument with satisfying results.
Manual perimetry has certain inherent limitations stemming from both the patient and the examiner. Automated perimetry, if properly developed, can offer the advantages of exact reproducibility of the examination strategy, accuracy achieved through averaging of repeated determinations, and systematic application of previous data to the current examination. The history, concepts and clinical practically of automated perimetry are discussed. Several systems capable of performing functions resembling human intellectual activity are commerically available; one, the OctopusTM, is described in detail.
We describe our initial clinical trials comparing the Fieldmaster automated visual field plotter (Synemed, Inc) with Goldmann kinetic perimetry performed by highly skilled perimetrists. The Fieldmaster utilizes a quick, randomized test procedure referred to as 'suprathreshold static perimetry.' The calibration and stimulus control features of the Fieldmaster have made it possible to derive approximate Goldmann-equivalent stimulus values and provide accurate, reproducible test conditions. Evaluation of 105 eyes (61 with defects, 44 normal) revealed a 98.5% detection rate and a 4% false alarm rate for the Fieldmaster in comparison with Goldmann kinetic perimetry. Based on these results, the Fieldmaster appears to have great potential value as a quantitative visual field screening device for the detecion of visual field defects.
Automatic perimetry was performed in 2998 eyes of 1511 subjects comprising 78% of all persons born 1907--1921 and resident in a certain small area. Unreliable or abnormal tests were repeated. The average number of tests per person was 2.25. About 90% of all tests in normal eyes were performed in less than 3 min. The screening was considered negative in 2887 eyes, incomplete in 20 eyes and positive in 91 eyes (3%). Eighteen of the positives were previously unknown glaucomatous defects. There was only one unexplained "false positive". We concluded that the method is quick, sensitive, specific and dependable. The apparatus is simple to manage and cheap to run.
One hundred fifty-one eyes of 101 consecutive patients with chronic open-angle and low tension glaucoma showed typical visual field changes. Sixty of the eyes had a nasal step, either alone or in combination with other defects. In 17 of these eyes, it was possible to demonstrate an isolated scotoma in the nasal periphery. It was concluded that the peripheral nasal step is a nerve fiber bundle defect that in its earliest phase produces a scotoma. In this sense, it behaves similar to the more central defects, rather than simply as a depression of isopters nasally.
• Twenty-two eyes of 22 patients with initially normal visual fields developed glaucomatous field defects. In 13 of these, the development of the definitive field defect was preceded by a localized minor disturbance in the area where the defect appeared subsequently. In a control group of 22 ocular hypertensives without field defects, six eyes had localized disturbances similar to those that preceded the field defects in the study group. This type of minor localized disturbance may represent an early glaucomatous visual change detectable before the appearance of definitive scotomas.
(Arch Ophthalmol 95:1173-1175, 1977)
It may be postulated that, in proportion as the defects are smaller, as the intensity is less, as the defects are situated more centrally, and as the changes in the defect are smaller and slower, the more static perimetry is to be taken into consideration. Static perimetry records the form of defects in a new manner and offers new diagnostic possibilities. Moreover, static perimetry enables one to lay down the intensity of defects also quantitatively, analogous to the loss of visual acuity.
Six hundred twenty-one subjects with an applanation pressure of 20 mm Hg or greater in both eyes and a visual acuity of 20/30 or better were examined for glaucomatous field defects by selective perimetry using the 1-2 and 1-4 targets of the Goldmann perimeter. Significant defects included paracentral scotomas, nasal step, and pressure dependent contraction of the isopter. These defects were present in 106 eyes. Only two required the 1-4 target. Eleven required isopter determination with the 1-2. Ninety-three were detected by stationary presentation at 5, 10, and 15 circles. The frequency of field defects increased significantly with age and with applanation pressure level.
In some experiments it was proved that both the level and the variation of the differential threshold of a single stimulus is the same as the level and variation of the threshold for this stimulus when presented simultaneously with 2 or 3 other stimuli (multiple stimulus). The stimuli were presented as the corners of a triangle (or quadrangle) with the fixation object in the centre of this triangle, the smallest distance from stimuli to fixation object was 2°. The largest distance was 25°. Thresholds for single and multiple stimulus presentation were the same for all eccentricities, for regular and irregular spatial presentation, for presentation at threshold level and at suprathreshold level of the multiple stimuli. The importance of these findings for visual field investigation is discussed.
A warning is given against the incorrect use of the Visual Field Analyser. The recommended filter dial positions and the differences in threshold luminance between the various stimuli are discussed.
Fifty-one consecutive patients with primary open-angle glaucoma had 81 eyes with glaucomatous field loss. Peripheral nasal step field defects were found in 21 eyes (26%) and in nine of these the nasal step was the only demonstrable glaucoma field defect.
The possible applications of computer-assisted static perimetry are examined after five years of personal controlled studies of different types of computerized perimeters. The common advantage of all computer-assisted perimeters is the elimination of the influence of the perimetrist on the results. However, some perimeters are fully computer-assisted and some are only partially so. Even after complete elimination of the perimetrist's influence, some physiological and psychological influences remain due to the patient and will cause fluctuations of the results. In perimeters, the density of the grid and the adaptive strategy of exact threshold measurement are important in obtaining reproducible results. A compromise between duration of the test and exactness has to be found. The most acceptable compromise seems to be an uneven distribution of stimuli, which form a denser grid in areas of special interest and a wider grid in areas less likely to be involved, combined with exact threshold measurements only in suspicious areas. Multiple stimulus presentation is not adequate. High sensitivity of screening is not a great advantage, unless combined with a high specificity. We have shown that using the same stimulus luminosity for center and periphery (a nonadaptive strategy) produces nonspecific results. Only an adaptive strategy can result in high sensitivity and specificity. Adaptive strategy means that the luminosity of the stimulus is adapted to the individual threshold curve of the visual field. In addition, the exact individual thresholds are bracketed by small up and down steps of variation in luminosity. In some cases, scanning programs with two levels of adaptation can be sufficient. The user of modern perimeters must understand such terms as: asb, dB, presentation time, and diameter of stimuli. Projection of stimuli is preferred to light emitting diodes or glass fiber optics. The programs (software) of the modern instruments are of the greatest importance, because the clinical experience that the perimetrist had to acquire in previous manual perimetry is incorporated in these programs. In the Octopus perimeter a delta program is available that differentiates patient fluctuations that may be insignificant from directed significant alterations of the field which might require alteration of therapy. The programs are listed for different computer-assisted perimeters, and their choice is described. The costs of the perimeters are also given. Many controlled clinical studies are quoted briefly where they are useful for understanding the discussion. A brief chapter deals with the reliability of the perimetric test.(ABSTRACT TRUNCATED AT 400 WORDS)
We used a blue stimulus on the Friedmann visual field analyzer for static spot-checking for glaucomatous defects. In the 60 eyes tested, the blue stimulus was not more sensitive in detecting glaucomatous defects than the white stimulus.
The central visual fields of 44 optometric patients with known or suspected field defects were measured with the Friedmann Visual Field Analyser (FVA) and a 2-m tangent screen. The clinical correlation of visual field characteristics was at least adequate in more than 90% of eyes. Statistically significant correlations were also found between the area of scotoma found on the tangent screen and (1) the number of locations with reduced sensitivity and (2) the average reduction in sensitivity of the stimulated locations as determined by the FVA.
Automated (Fieldmaster) and manual kinetic perimetry were performed in 1,019 eyes with various visual disorders. tunder appropriate test conditions, automated Fieldmaster evaluations showed a 96.1% detection rate and a 4.7% false alarm rate for detection of visual field defects. Preliminary results for 168 eyes showed that sequential follow-up testing with the Fieldmaster correctly identified progression or regression of visual field loss in more than 94% (34 of 36) of the eyes with visual field changes. The Fieldmaster correctly determined no change in visual field characteristics for 99% (131 of 132) of the eyes with stable visual fields. These data indicate that the Fieldmaster is an excellent device for detecting visual field defects, and also has some capabilities for monitoring progression or regression of visual field loss.
Extrafoveal vision is one of the most important of all ocular functions. It is essential to locomotion, and, in this era of rapid movement, it is of greater protective value to the human organism than any other of the special senses. Certainly it is of more importance today than ever before in history. A correct analysis of abnormalities of the visual field has a diagnostic value in disease of the entire visual pathway that can hardly be overemphasized. Ocular dysfunction is frequently reflected in defective visual fields as are disease in the entire supratentorial compartment of the intracranial cavity and some general systemic disturbances of both somatic and psychic origin. Examination of the visual field includes many methods and devices. Most of them are cumbersome and difficult to use with any degree of both speed and accuracy. The complexity of the methods available, the time required to apply these methods
The development of the multiple-pattern tachystoscopic visual field screener by Harrington1 has made a highly useful new tool available to all interested in the detection of and care of glaucoma. Its usefulness in industrial medicine and other fields is also being increasingly documented.2
Both the need for epidemiologic study of primary glaucoma and the infinitely greater effectiveness of therapy undertaken early in the course of the disease make a reasonably accurate screening procedure for glaucoma a highly desirable goal, and some form of visual field testing can scarcely fail to be included in such a procedure. Since the timeconsuming nature of classic methods of central field testing, plus the need for skilled operators to perform the test, almost precludes their use in mass screening techniques, the multiple-pattern tachystoscopic visual field screener has appeared to offer the best substitute yet found which can fill the needs for a reasonably
Introduction
In the Department of Ophthalmology at the University of Michigan it was noted that the peripheral fields rarely demonstrated a defect that the central fields (Bjerrum screen) failed to show. It was this observation that initiated the present study. In this paper it is not our intention to discuss the ultimate fine points that might be gleaned with research field techniques but rather to emphasize that our methods closely approximate the techniques used in the average clinic and ophthalmologist's office.J. P. F. Lloyd summed up the situation well by stating, "... there is no provision for anything between the magnificent fields taken by Traquair and his literal followers which appear in publications such as that of Hughes (1943) on the one hand, and on the other the hurried scrawlings and weird frescoes found attached to hospital notes, such as these.... It is important to realize that only in ideal
Although the incidence of blindness in the United States is the lowest of any major nation (54 per 100,000), preventable blindness still occurs far too frequently. Despite the efforts of the ophthalmologists, the general practitioner, and the public health workers, there are now 17,000 legally blind persons in Ohio—enough to populate a small city. Improvement of these statistics of tragedy would be possible by application of existing knowledge through earlier detection and treatment of serious eye diseases.
A proven and fruitful method for early detection of serious disease is the widespread use of well-chosen screening procedures. The objective of a screening procedure is not to diagnose disease but to detect persons who are likely to have disease, in order to permit referral for definitive study and care. The ideal screening method should not fail too many normal persons (false-positive result) and, more important, should not overlook any case of disease