Abstract

Although acuity tests adequately document visual loss in patients with spherical and/or astigmatic refractive error, acuity tests incompletely describe or even fail to detect visual loss in some patients with visual pathway dysfunction at retinal, optic nerve, and cortical levels. Sine wave grating contrast sensitivity tests reveal four kinds of loss: (1) selective low, (2) selective intermediate (notch), (3) selective high, and (4) general. (Many patients show mixed loss.) Acuity tests detect classes (3) and (4) only. Low and/or notch loss can be produced by monocular diplopia even in the presence of 20/20 acuity and can be induced by the test procedure, but when such cases are eliminated, cases remain whose visual loss can be attributed to selective vulnerability of neurons that prefer targets of low and/or intermediate spatial frequencies. It is known that some patients with multiple sclerosis (MS) experience orientation-specific loss that can vary over the visual field, suggesting patchy involvement of cortical neurons. Sensitivity loss can be accompanied by discrimination loss including reduced ability to discriminate between different target sizes and orientations. In MS the pattern of loss can change dramatically over short time periods especially in patients with Uhthoff’s syndrome. In patients with ocular hypertension, low frequency loss that spares visual acuity has been attributed to selective damage to large (alpha) retinal ganglion cells. Low-contrast letter charts provide a simple shotgun test of sensitivity and/or discrimination that distinguishes pathway involvement from a purely refractive problem and can detect hidden visual loss in 20/20 (or better) eyes of patients with pathway involvement including macular degeneration, diabetes, glaucoma, ocular hypertension, Parkinson’s disease, and MS.

© 1986 Optical Society of America