Gillray L. Kandel

Are the Dominant Eyes of Amblyopes Normal

Abstract The common assumption that the dominant eyes of unilateral amblyopes are normal eyes is shown to be unjustified. The dominant eyes of unilateral amblyopes are shown to have reduced sensitivity, reduced acuity, and a horizontal eccentricity of fixation when compared to eyes of persons with normal acuity and normal binocular fixation.

Preferential Looking as a Guide for Amblyopia Therapy in Monocular Infantile Cataracts

Despite recent advances in surgical technique and refractive correction, amblyopia remains a significant problem in the treatment of monocular infantile cataracts. Amblyopia therapy recommended by different authors during the preverbal period has varied from no patching to nearly full-time occlusion of the phakic eye. We measured preferential looking (PL) acuities sequentially in four infants following monocular cataract surgery and contact lens correction. This information was used to adjust occlusion of the phakic eye, which was prescribed 25%-100% of waking hours. Patching schedules were altered, on average, every three to four months in response to changes in PL acuities. Four increases in patching intensity retarded acuity development in the phakic and benefited development in the aphakic eyes. Nine decreases enhanced progress or yielded no change in the phakic and, with two exceptions, impeded progress in the aphakic eyes. Recognition acuities now available for two of the children show continuity with previous PL acuities and confirm useful vision in the aphakic eyes. We describe guidelines for adjusting occlusion based on our experience. We believe that PL modulation of patching therapy may result in more favorable visual outcomes for both eyes of infants with monocular cataracts.

Monocular fixation and acuity in amblyopic and normal eyes.

&NA; We studied the relation between eccentricity of monocular fixation and the minimum angle of resolution in visually normal subjects and in both the amblyopic and dominant eyes of amblyopes. For the amblyopic and visually normal eyes, this relation was linear; resolution was poorer at the eccentrically fixating locus than at the corresponding region of the normal eye. The dominant eyes of the strabismic amblyopes had a nasal component of eccentric fixation that was less than that of the companion amblyopic eyes, but greater than that found in the visually normal eyes. In terms of the eccentricity of monocular fixation, the dominent eyes of strabismic amblyopes were different from the normal eyes.

THE MINIMUM ANGLE OF RESOLUTION VS ANGLE OF REGARD FUNCTION AS MEASURED WITH DIFFERENT TARGETS

Abstract Although the minimum angle of resolution (reciprocal visual acuity) may be well approximated as a linear function of angle of regard, a fresh look at past research using several target types and spanning a wide luminance range indicate that a small but distinct monotonic nonlinearity exists in the function.

Near-Final Scotopic Thresholds in Normal Eyes and in the Dominant Eyes of Amblyopes

Near-final scotopic thresholds of dominant eyes of amblyopic subjects and age-matched persons with bilaterally normal vision were compared in three substudies. As a group, dominant eyes were found to

Experimentally induced variations in the dark adaptation functions of a severe strabismic amblyope

Dark adaptation curves were determined for an amblyopic and a normal control subject following a variety of preadaptation conditions. Sizable between-eye differences were found in the dark adaptation functions of only the amblyope; the magnitude of such differences varied with this subjects distance from the light preadapting screen and with the effective size of his pupils during the light preadaptation period. Marked differences were also found between the dark adaptation functions of both eyes of the amblyopic subject and those of the normal subject. The preadaptation-dependent changes in the dark adaptation function of the amblyopic subject are hypothesized to result from anomalies of amblyopic eye light adaptation which are referable to disturbances of retinal receptor alignment

A precise method of measuring fixational eccentricity using the Maxwell spot centroid

An improved version of a method which uses the Maxwell spot to measure eccentricity of fixation is described and discussed. The method determines the centroid of the macula psychophysically and locates the position of this centroid with respect to the point the O uses for fixation. The distance between these two points is a measure of eccentricity of fixation. It is estimated that the present method has an instrumental error of about 0.1 deg.

Eccentricity of the scotopic fovea about a photopic point as revealed by acuity contours.

Abstract Both photopic and scotopic (Vernier offset) acuity contours were determined along the horizontal and vertical meridians for 6° on either side of visual field center. The photopic contours evidenced bisymmetry about a photopic fixation point coincident with the center of the target. Scotopic contours, on the other hand, were not symmetrical about this same fixation point. A half maximum acuity criterion was employed to obtain a measure of contour symmetry along a specific meridian. The authors conclude that the physiologic foveal scotoma, as mapped by retinal acuity, is decentered with respect to a photopic point of fixation.

Classically conditioned limb reflexes reinforced by motor cortex stimulation

Abstract This study measures the latencies of, and the effect of the reduction of the interreinforcement time interval upon, conditional limb reflexes reinforced to an auditory conditional stimulus with movement evoking electrical stimulation of the motor-sensory cortex as the unconditional stimulus. Conditioned head movements were obtained in all, while limb movements developed in only 2, of 3 cats following 4.6 min reinforcement intervals. One-min reinforcement intervals did not abolish these limb responses which are here shown to have a latency significantly in excess of 1 sec. The conditional limb responses of this study are identified as a classical, as contrasted with the instrumental variant of other studies. The classical limb response is thought to develop if there is: (a) an absence of head movement induced extensor tonus; (b) a motor-sensory cortex stimulus adequate to evoke limb movement; and, (c) a period of conditional stimulus isolation ample to permit the observation of these long latency responses.

Pseudo-facilitation of conditioned avoidance by interposed insulin hypoglycemia ☆

Abstract Following the procedure of Gellhorn and Minatoya, insulin hypoglycemia is induced in two groups of 8 rats after they are trained until they make two successive CARs in a shuttlebox. Those rats who receive massed, no more than 20 trials per day, pretreatment training give more CARs after treatment than a similarly trained saline control group. This result agrees with the one reported by the above authors. However, when the hypoglycemia is induced in rats who received spaced pretreatment training of not more than two trials per day, the experimental animals give fewer CARs than similarly pretrained control animals. The latter result is at variance with the one reported by the above authors. A disinhibitory and deleterious role, rather than a facilitating one for hypoglycemia is hypothesized. Some aspects of Hulls behavior system are seen as relevant to experiments which claim learning facilitation. The conditions which warrant the use of facilitation as a construct in learning studies are briefly examined.