New methods for discriminating neural and optical losses of vision

Visual acuity, the premier test of visual function, is analyzed as a three-stage, hierarchical sequence beginning with the detection of spatial contrast, followed by the resolution of that contrast into spatially separate elements, and ending with the identification of a particular arrangement of elements as one of several possible test objects, e.g., a letter in the Snellen alphabet. Each stage in this process has its own inherent limitations which are associated with different stages of the visual pathway. New methods are described for testing each stage of the hierarchy individually for the purpose of identifying the weak link in the chain, thus paving the way for differential diagnosis of optical and neural losses of vision.