STRUCTURAL BASIS OF AMBLYOPIA & STRABISMUS

点击翻译按钮获取中文摘要

Significance Strabismus (also known colloquially as "crossed eyes") affects visual function in 2% of the American population. Our research is directed at elucidating the structural changes in the primate visual cortex, which occurs, from strabismus. Objectives In primate striate cortex, geniculocortical afferents in layer IVc terminate in parallel stripes called ocular dominance. This segregation of ocular inputs generates a related but distinct columnar system of monocular core zones alternating with binocular border strips. Evidence for this functional parcellation was obtained by comparing the effects of enucleation, eyelid suture, and retinal laser lesions on cytochrome oxidase (CO) activity in 8 macaques. Our goal was to learn how binocular, stereo-sensitive cells are organized in the visual cortex. Results Enucleation produced a high-contrast pattern of dark and light columns in layer IVc, corresponding precisely to the ocular dominance columns, whereas eyelid suture produced a low-contrast pattern of thin dark columns alternating with wide pale columns. [3H]proline eye injection showed that the thin dark columns corresponded to the core zones of the open eye's ocular dominance columns. The wide pale columns resulted from loss of CO activity in the sutured eye's core zones and within both eyes' border strips. Loss of CO activity within both eyes' border strips suggests that these regions are binocular. TO confirm our findings, we compared different CO patterns in the same cortex by making retinal laser lesions in 4 animals. They produced a CO pattern tantamount to "focal" enucleation, although contrast was low when laser damage was confined to the outer retina. CO levels in cortical scotomas remained severely depressed for months after retinal lesions, even when the other eye was enucleated. This observation provided little anatomical support for the notion to topographic plasticity after visual deafferentation. In a single human subject with macular degeneration, CO revealed a low-contrast pattern of ocular dominance columns, resembling the pattern in monkeys with laser-induced photoreceptor damage. Future Directions Analysis of the changes in metabolic activity, which occur in ocular dominance columns as a result of visual suppression, induced by strabismus. KEY WORDS strabismus, visual cortex, ocular dominance FUNDING National Eye Institute, RO1 EY 10217-06 PUBLICATIONS Horton, J.C., and Hocking, D.R., Monocular Core Zones and Binocular Border Strips in Primate Striate Cortex Revealed by the Contrasting Effects of Enucleation, EyelidSuture, and Retinal Laser Lesions Upon Cytochrome Oxidase Activity. Journal of Neuroscience,18:5433-5455,1998.