Since different writers use the term "amblyopia ex anopsia" to express radically diverse ideas, it is needful to define its meaning in this discussion. Negatively it is not applied to a dulness of vision induced either by an organic lesion, which can be objectively seen with the ophthalmoscope or otherwise; nor by exclusion of light from the retina, in part or whole, during long periods; nor by defective refraction or disturbed muscular equilibrium of either ciliary, rectus or oblique muscles. Positively it is applied to that dulness of vision which attends the inability of the brain to recognize impressions sent it from the retina.
As to the nature and causes of the dulled vision, we have three widely differing views. The first contends that the brain actively inhibits the visual center from receiving impressions, until it loses its receptive power in whole or part; the second says that the brain