Is amblyopia a peripheral defect?

Abstract

A class of retinal ganglion cells, the 'sustained' or 'X' cells in the area centralis of the retina, provides the physiological basis of high visual acuity. Our hypothesis, that amblyopia is a functional loss of X-cells due to inappropriate stimulation of the fovea by habitually blurred images during the critical period of development, has been supported by experiments on kittens reared with various types of surgically produced squint or with penalization. Amblyopia was associated with a loss of visual acuity of X-cells in the area centralis of the squinting eyes which had lost the ability to fix or of the penalized eyes, i.e. amblyopia occurred in the eyes which received habitually blurred images during the critical period of development. Thus amblyopia has a peripheral (retinal) cause. Regardless of whether or not the eye was amblyopic, a loss of binocularly driven cells in the visual cortex was a common feature in all uniocularly treated cases. When one eye was amblyopic the cortical cells tended to favour the non-amblyopic eye and the number of cells driven by the amblyopic eye was reduced. These central effects may play a role in suppressing unwanted images from the amblyopic eye while the fixing eye is in use. But the central effects do not cause amblyopia.