Congenital myopic esotropia: a case study

A congenital myope developed a 20 delta left esotropia at 8 months of age. His eyes aligned immediately with a -4.00 D correction and would become esotropic when the glasses were removed. Before eyeglass wear best corrected acuity was reduced for both eyes with the left eye acuity significantly lower than the right. From age 8 to 12 months with part-time eyeglass wear, acuity improved and became equal for the two eyes. At 12 months of age the eyeglasses were lost and within 1 month the strabismus no longer responded to minus lenses and amblyopia reappeared in the left eye. This indicates that a myopic infant may stop bifixating blurred images beyond his far point and then cease to be able to relax convergence thereafter. It has the broader implication that tonic vergence posture and AC/A ratio may develop according to the visual experience of each infant.

Pre-stereoptic binocular vision in infants

In a preferential looking experiment, identical patterns (vertical stripes) were presented to both eyes on one of two screens while orthogonal patterns (vertical stripes in one eye and horizontal stripes in the other) were presented on the other screen. Most infants younger than 3.5 months of age originally showed a preference for the dichoptic (interocularly orthogonal) pattern. At an average age of 3.5 months, however, they showed a sudden shift of preference from this pattern to the interocularly identical pattern. The full shift from a preference for one stimulus to the other (both statistically significant) occurred within a few weeks in most cases. The onset age of the shift in preference agreed with the onset age of fusion-rivalry discrimination found in a previous study (Birch et al., 1985). The original preference for the bincularly orthogonal patterns may be interpreted as a preference for a grid (interocularly emergent intersections) over a grating, judging from results of two control experiments. These data suggest that the pre-stereoptic system non-selectively combines information from the two eyes without regard to edge orientation because it loses eye-of-origin information at a relatively early stage of binocular visual processing. Thus, the pre-stereoptic system does not have the capability of interocular suppression. The theoretical and clinical significance of the new findings are discussed along with a neuronal model of cortical development of ocular segregation and binocular pathways.

Preferential-looking assessment of fusion and stereopsis in infants aged 1-6 months

The ability of infants to discriminate zero-disparity stimuli from both reverse contrast (rivalrous) and disparate (stereoscopic) stimuli was investigated in a two-alternative, forced-choice, preferential-looking paradigm. Few infants under 4 months of age demonstrated discrimination for any stimulus pairing. Of the infants tested at 4 months of age, approximately 70% preferred zero-disparity stimuli to reverse contrast stimuli, and 82% preferred stereoscopic stimuli to zero-disparity stimuli. Nearly 100% of 5- and 6-month-old infants exhibited these preferences. These findings suggest that sensory fusion is not present at birth but develops rapidly over the first 6 months of life. The time course for the development of sensory fusion was similar to the time course for the development of stereopsis in nine infants tested longitudinally.

Development of vernier acuity in infants

The development of vernier acuity in human infants aged 2-9 months was assessed by a preferential looking procedure using a vernier-motion display. The displacement of vernier offsets gives the impression of motion only when the vernier offsets are detected. Grating acuity of the same group of infants was also measured by a preferential looking procedure. Vernier acuity was found to be superior to grating acuity only after 3 months of age. This superiority of vernier acuity was compared with the superiority of stereoscopic acuity to grating acuity. The two classes of hyperacuity proved to be almost equivalent in terms of their developmental time-courses. A common physiological basis for the development of hyperacuities is suggested.

Adaptation to the reversal of binocular depth cues: effects of wearing left-right reversing spectacles on stereoscopic depth perception

The principle of stereopsis, that crossed disparity causes a convex perception and uncrossed disparity a concave one, has for a long time been considered to depend on a very rigid neural mechanism not affected by experience. Experiments are reported here which show that this relationship between disparity and perceived depth can be reversed by experience. An observer wore a pair of left-right reversing spectacles continuously for nine days. The spectacles also reversed the relation between the direction of perceived depth and the direction of binocular depth cues, ie disparity and vergence. For a period starting two days before wearing the spectacles and continuing until seventy-nine days after their removal the observer was examined with a haploscope and an electrooculograph. All the stereoscopic experiments were carried out without spectacles in order to examine some aftereffects of wearing spectacles. For the stereograms with linear contours not only the adaptive reversal of the relation between disparity and perceived depth, but also some abnormal depth perceptions and long-lasting aftereffects were found. For Julesz's random-dot stereograms, however, in which contours can be seen only after binocular combination, no adaptive change or reversal occurred. These results suggest that the process of stereopsis consists of two concurrent subprocesses.

Electromyographic study of patients with dysfunction of the Eustachian tube

In order to determine how often dysfunction of the tube might arise from dysfunction of the tubal muscles, electromyographic examination of the muscles was carried out on 34 patients with occluded or patent tube. Using a monopolar needle electrode inserted through the nose, selective EMG of the tensor and levator veli palatini muscles were picked up during swallowing. It was found that the patients showed neither abnormally reduced nor increased muscle activity. Comparison of muscle activity of the normal tube and of both the occluded and patent tube revealed no significant differences. Therefore, myogenic cause of tubal dysfunction seems improbable from the clinical viewpoint.