The Limitations of Kinetic Perimetry in Early Scotoma Detection

THE LIMITATIONS OF KINETIC PERIMETRY IN EARLY SCOTOMA DETECTION GERALD L. PORTNEY, MDt and

MARIJANE A. KROHN, MA BY INVITATION

DAVIS, CALIFORNIA When tested by Goldmann kinetic perimetry ten patients with glaucomatous optic disc cupping had no visual field defects. but visual field defects were detected when tested by threshold static perimetry on the Tubingen perimeter. To improve the detection ability of kinetic perimetry, we suggest placing the interisopter spot-checks closer together or expanding the central 30° plotting area.

information obtained is directly proportional to the number of isopters plotted.

The likelihood of detecting a visual field defect of a certain minimum size depends upon the number of locations examined. To test every 10 square area of the central 30 0 field would require nearly 3,000 measurements, a task INTRODUCTION which greatly exceeds the practical KINETIC perimetry is the most limits of perimetric testing. A thorcommon method of visual field test- ough kinetic examination of the ing for glaucoma and ocular hyper- entire visual field generally intensive patients. The examiner cludes between 60 and 100 points, moves a target of specified lumi- with an additional 100 points pronance and size from the periphery vided by suprathreshold spot-checktoward the center until the patient ing between isopters. This amount first detects it. An equal-sensitivity of information limits the ability of circle or isopter is generated by kinetic perimetry to reliably detect repeating measurements along visual field defects. many meridians, recording the Another factor affecting the early results, and connecting the locadetection of visual field defects is tions on paper. By using stimuli of various sizes and luminance values, the luminance of the test stimulus. the perimetrist produces multiple Large intervals between target isopters. The amount of visual field luminance values may produce substantial distances between isopters, leaving many intermediate locaSubmitted for publication Sept 29, 1977. tions untested. Spot-checking beFrom the Department of Ophthalmology, School of tween isopters may test these locaMedicine, University of California, Davis. tions, although shallow scotomata tOr Portney died May 23, 1977. will be missed if the target is too Presented at the Eighty·second Annual Meeting of bright. Other factors which may inthe American Academy of Ophthalmology and fluence detection capabilities during Otolaryngology, Dallas, Oct 2-6, 1977. kinetic perimetry are: uniformity of Reprint requests to Department of Ophthalmology, School of Medicine, University of California, speed, direction of target motion, target size, patient reaction time, Davis, CA 95616 (Mariiane A. Krohn, MA). 287

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refractive error, and the patient's visual sensitivity gradient. Although static perimetry is a more time-consuming method of visual field testing, it has greater stimulus control which eliminates many of the problems associated with kinetic perimetry. This technique measures the light sensitivity threshold at close intervals along selected meridians, yielding a profile of visual sensitivity. Most examiners perform static perimetry to further evaluate defects which kinetic perimetry or screening procedures have already detected. In 1967, Drance et alI reported that tangent screen kinetic perimetry failed to find some visual field defects which were subsequently detected by threshold static perimetry, a topic infrequently discussed in literature since then. Although the Goldmann perimeter allows for more accurate stimulus conditions and easy spot-checking in kinetic examinations, it leaves visual field defects undetected. This paper describes a series of ten eyes in which careful kinetic perimetry on the Goldmann perimeter failed to find a visual field defect, which threshold static perimetry along preselected meridians subsequently revealed.

METHODS From approximately 200 patients with glaucoma and ocular hypertension, tested by both perimetric methods, seen from 1975 through 1977 at the University of California, Davis, we selected ten patients with threshold static visual field defects not previously revealed by kinetic perimetry. Before we

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found the visual field defect by threshold static perimetry, five patients were originally considered ocular hypertensives, with no previous visual field defects in either eye. All five ocular hypertensive patients had optic disc defects associated with the visual field defect, which were later detected by threshold static perimetry. The fellow eyes had high pressures but normal discs and fields. The other five patients were originally considered glaucoma patients because of visual field defects in their fellow eyes. However, the visual field defect we detected by threshold static perimetry was the first visual field defect detected for the eye included in the study. These were also associated with glaucomatous optic disc cupping. The ten eyes were refracted to 20/ 25 or better; the pupils were 4 mm or larger; and the eyes had no other pathologic conditions. The Goldmann kinetic visual field examination preceded the Tubingen static threshold examination by a maximum of one month. For the kinetic examination on the Goldmann perimeter, patients used their best manifested refraction with the appropriate amount of plus lens for their age, distance of the perimeter bowl, degree of cycloplegia, and spherical equivalent for the cylinder. Within the central 30° the perimetrist plotted two or three isopters, measuring at least 14 points per isopter. Between each set of two isopters, the perimetrist spot-checked with the target which had mapped the larger of the two isopters. This is called suprathreshold static spot-checking. These checks were at 5° intervals from the center along each 15° meridian. Inside the smallest isopter, the size of the fixation device limited spot-checking to within 2°

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of the center. Perimetrists performed these tests without the aid of an eccentric fixation device, although the results indicate that the central fixation device did not mask any of the defects. The kinetic perimetric examination was completed with one or two peripheral isopters (Fig 1). IZO

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lected to intersect the meridian at the deepest level of the defect. With the degree of eccentricity thus established, the threshold was measured at every 15° meridian until the entire circle was plotted. We used conservative criteria for accepting a visual field defect by static perimetry. The defect must be at least 5° wide and 0.5 log units deep, and both ofthese size requirements must be confirmed by circular static perimetry through the center of the meridional defect.

RESULTS

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Fig I.-The placement of isopters and suprathreshold spot-checks in typical kinetic examination on Goldmann perimeter.

The perimetrist tested patients on the Tubingen perimeter for the threshold static perimetry, using their best manifested refraction with the appropriate amount of add, as determined for the kinetic examination. The kinetic perimetry provided no clues for choosing a location for the static meridians; therefore, the perimetrist arbitrarily tested four meridians for each eye: 45°, 135°, 225°, and 315°. A lO-minute target was used to measure the threshold at every degree out to 20° and then at 2° intervals out to 30°. If the perimetrists found a defect on any of the four standard meridians, they retested the area in a circular plotting pattern, verifying each defect by at least two threshold static plots. The circular threshold static profiles were se-

The size, shape, and location of the ten defects reveal several interesting features. The most frequent regions affected were the superior temporal and inferior nasal quadrants with four defects each. One defect was present in each of the remaining two quadrants. Between 0° and 10° from fixation five defects were found; the other five were between 10° and 20°. Defects within 10° of fixation did not show a predilection for any particular quadrant. Grouping defects by size showed that most were narrow; eight defects were between 5° and 10° wide and two between 10° and 13°. Width was determined on the standard four testing meridians. There were five defects smaller than 45° long and five were greater than 55° long, the maximum being 120° long. The length represents the degrees of arc measured on the circular static profiles which verified the meridional defects. Long defects did not group in any particular range of eccentricity. Between 1.0 and 1.8 log units in depth there were eight defects, and two defects were between 0.5 and 1.0 log units deep (Fig 2).

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Goldmann chart paper's small scale plotting area in the central 30 0 • Several deep, narrow defects were medium length (Fig 3) and several were up to an entire hemi-field long (Fig 4). Of the ten defects, two did not fit the deep, narrow trough pattern. They were comparatively shallow, more nearly round, and might have been detected during the kinetic examination by a dimmer stimulus for spot-checking. The two profiles of threshold static perimetry are shown in Fig 5; the Goldmann chart demonstrates how the defect might have appeared if plotted kinetically.

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As a group, these defects were deep, narrow, slit-like troughs in the island of vision. They are difficult to plot with kinetic perimetry because of the shape and the

The number of missed scotomata is probably much greater than indicated in the current study. Using

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less stringent criteria and examining a greater number of meridians with static perimetry would probably detect more instances than these ten cases. DISCUSSION

lengthy to use in the entire central field as a detection procedure. However, the complementary interaction between th~ tests is disrupted by finding defects with threshold static perimetry not found by kinetic perimetry.

In current perimetric testing procedures, kinetic perimetry usually serves as a method of detection; threshold static perimetry is generally a secondary test to analyze defects found by kinetic perimetry. This sequence allows a more economic investment of the time necessary for static perimetry on patients who have clinically important visual field defects. Static perimetry is manually performed and too

In view of the practical limitations of manual static perimetry, kinetic perimetry testing methods should be improved to detect a larger percentage of visual field defects. To improve the probability of detecting the deep, narrow, trough-like defects, the perimetrist can move the spot-checks between isopters closer together than 15° intervals circularly and 50 intervals meridionally. The small-scaled area on the

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Goldmann chart paper for the central 30 0 makes it difficult to test every 2.5 0 accurately. A perimetrist would be placing spot-checks every 3 mm on the chart paper. The pantograph arm on the Goldmann perimeter has a large amount of play in its movement, so attempts to place spot-checks every 3 mm on the chart paper would not yield testing intervals every 2.5 0 on the perimeter bowl. Despite the theoretic inaccuracies associated with a concentrated pattern of spot-checks, it might increase the percentage of defects found by kinetic perimetry. A second factor complicating the accurate plotting of small narrow defects is the patient's normal re-

fixation movements. Microsaccades, with an amplitude of 3 0 to 40 , could mask a narrow nonseeing area in the field by intermittently positioning a seeing area in front of the critical test position. This factor might affect suprathreshold spotchecks during a kinetic detection procedure more than a threshold static profile, because a perimetrist spends a smaller amount of time in an area with spot-checks than with threshold static measurements. The increased time spent permits microsaccades to frequently reposition the eye in an alignment which allows the detection of the defect. We missed two defects because spot-checks were too bright for the

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depth of the defect. Rather than estimating the sensitiVity gradient between isopters to select a dimmer suprathreshold test object theoretically for an area, a perimetrist could plot an additional one or two intermediate isopters with appropriate spot-checks. However, this plan only temporarily upgrades present detection methods until better methods of detecting defects are determined. To further improve presently available kinetic perimetry, any method of expanding the plotting area of the central 30° would aid in detecting these easily missed slit defects. Our clinical experience indicates that these defects are easier to plot kinetically on the expanded central 30° Tubingen chart paper, although we have not formally compared it with kinetics on the Goldmann perimeter. Lacking a Tubingen perimeter, a perimetrist might have equal success with the expanded testing area on a tangent screen. In 1969, Theo Schmidt2 recommended a modification for the Goldmann perimeter which doubled the testing distance to 60 cm, expanded the plotting area for the central 30°, and enlarged the area covered by paracentral scotomata. In the future, clinically useful automated suprathreshold and threshold static perimetry may detect these defects more accurately.

293 SUMMARY

When ten patients with glaucomatous optic disc cupping were tested by Goldmann kinetic perimetry, no visual field defects were detected, but visual field defects were detected when tested by threshold static perimetry. Deep, narrow troughs made eight defects difficult to detect. The other two defects were round, shallow defects, eluding detection by their shallowness. Placing spotchecks closer together and using dimmer stimuli may improve the detection ability of Goldmann kinetic perimetry, but improving detection methods is necessary in order to find a larger percentage of heretofore undetected defects. ACKNOWLEDGMENTS This in vestigation was supported by Public Health Service research grant EY 01841·01 from the National Eye Institute. After the death of Gerald L. Portney, MD, John L. Keltner, MD, and Chris A. Johnson, PhD, gave the second author invaluable aid in preparing the manuscript.

Key Words: Goldmann perimeter; Tubingen perimeter; threshold static perimetry; suprathreshold static perimetry; kinetic perimetry; detecting visual field defects; glaucoma; ocular hypertension.

REFERENCES 1. Drance SM, Wheeler C, Pattullo M: The use of static perimetry in the early detection of glaucoma. Can J Ophthalmol 2:249-258, 1967.

2. Schmidt T: Uber die Verdoppelung der Untersuchungsdistanz am Goldmann-perimeter. Doc Ophthalmol 26:286-294, 1969.