Binocular Summation within the Binocular Visual Field

To study the influence of binocular summation on the threshold values of the central visual field in normal subjects, the authors modified the Octopus 201 by combining it with the space synoptophore. They tested ten normal subjects between 20 and 30 years of age. A space synoptophore was built into the cupola of the Octopus 201 so that the authors could confirm the conditions of binocular vision while they measured the visual sensitivity of the visual field under the binocular condition. Sensitivity of the visual field was thus measured while fusional patterns were displayed by the space synoptophore. Forty-seven points in the central visual field were tested with the SARGON program. The mean sensitivity in the central visual field was 30.4dB in the left eye, 30.3dB in the right eye, and 32.0dB in both eyes. The visual sensitivity under the binocular condition was higher than that under the monocular condition. The difference in the foveal sensitivity was 3.7dB between the monocular and binocular conditions. Binocular summation of the visual sensitivity in the binocular visual field was observed, and it was highest in the fovea. Combining the Octopus 201 with the space synoptophore was quite useful for the assessment of binocular summation. Introduction One of the important functions in the realization of binocularity is the binocular interaction within the binocular visual field. The increase in the amplitude of the visual-evoked potential by binocular stimulation is well known1-4. However, there have been very few reports on the visual sensitivity of perimetry by binocular stimulation5,6. In order to examine the binocular interaction within the binocular visual field, it was necessary to confirm the condition of the binocular vision while the visual sensitivity was measured. To evaluate binocular summation, we modified the Octopus 201 by combining it with the space synoptophore and tested light sensitivity in normal subjects. Address for correspondence: Akemi Wakayama, C.O., Department of Ophthalmology, Kinki University School of Medicine, Ohno-Higashi, Osaka-Sayama City, Osaka 589-8511, Japan 27.p65 11/25/99, 11:43 AM 193 194 Akemi Wakayama et al. Material and methods The ten normal subjects were aged between 20 and 30 years. Their corrected vision was 20/20 or better, refraction was within 1.5 diopters of spherical error and 0.75 diopters of astigmatism, and the binocular function was 60 seconds of arc by the TNO stereo-test. None of the subjects had any systemic or ophthalmological diseases likely to affect visual function. Visual sensitivity was measured with the Octopus 201 (Interzeag) and the space synoptophore (TOPCON) developed by Iwai7. Two tubes of the synoptophore were removed, and half mirrors only were installed in the position of the reflection mirrors (Figs. 1 and 2). It was built into the cupola of the Octopus 201 in order to measure monocular and binocular sensitivities in the central visual field. Sensitivities of the central visual field under monocular and binocular conditions were measured, while the fusional patterns were displayed on the space synoptophore. The fusional patterns were a 3° square for both eyes, a 45° diagonal line for the left eye, and a 135° diagonal line for the right eye (Fig. 3). Octopus perimetry was performed with a stimulus size 3, under the background luminance of 4 asb. The duration of target stimulus was 100 msec. Using the SARGON program, we designed a new program to test 47 points, 37 of which were located in the central 6° visual field and ten on the horizontal meridian subtending 8°, 10°, 12°, Fig. 1. The modified Octopus 201 combined with the space synoptophore. 27.p65 11/25/99, 11:43 AM 194 Binocular summation within the binocular visual field 195 Fig. 2. Schematic drawing of the measuring device. A. The cupola of the Octopus 201; B. the space synoptophore; C. the half mirror. Fig. 3. Fusional patterns displayed on the space synoptophore. 27.p65 11/25/99, 11:43 AM 195 196 Akemi Wakayama et al. 16°, and 20° (Fig. 4). We measured each double circle twice for the purpose of calculating the short-term fluctuation. Each measurement was carried out twice, and the mean values were used to evaluate the visual sensitivities under monocular and binocular conditions. Statistical analysis was carried out using the Wilcoxon rank sum test.