Experimental analysis of amblyopia and strabismus COLIN BLAKEMORE

In the past few years physiological experiments have brought us a little closer to an understanding of some forms of developmental amblyopia-deficits of visual acuity of central, not retinal, origin, which are not correctable by optical means. While amblyopia has become a catch-all term that covers the symptoms of a multitude of disorders, there are certain stereotyped experimental procedures that invariably lead to gross disturbances in the visual system. In this paper we shall describe a few of these experiments and attempt to relate them to some of the clinical origins of amblyopia in man. The cat has been the subject of a great deal of research on the development of the visual system, though it is clear that most of the observations, with some minor differences, also apply to monkeys (see von Noorden, 1974). By extrapolation, the situation is probably similar in man. Cats, monkeys, and man are all highly binocular animals. They have roughly the same amount of binocular overlap of the two visual fields, and their eyes are extremely mobile, showing disjunctive as well as conjugate movements. There is now behavioural evidence that both cats (Fox and Blake, 197i) and monkeys (Bough, I970) normally have stereoscopic vision, being able to discriminate the relative distances of objects solely on the basis of the retinal disparity of their images. Indeed, from neurophysiological experiments there is now a fair understanding of the actual neural mechanism of stereopsis.