Contrast sensitivity changes in ocular hypertension and early glaucoma (summary)

Abstract

The visual system is organized to distinguish spatial and temporal elements at various levels of contrast. This ability depends on the neural subsystems including the small X and larger Y ganglion cells of the retina. X cells have high spatial contrast sensitivity, but low temporal contrast sensitivity. Just the opposite is true for Y cells. Patients with glaucoma show reductions in both spatial and temporal contrast sensitivity, which suggests that both the X and Y systems are damaged by this disease. Static and dynamic tests are used to assess contrast sensitivity. Static contrast sensitivity tests measure the threshold contrast at which gratings of varying spatial frequency become visible. Dynamic or temporally modulated tests utilizing diffuse and counterphase flicker measure the threshold of visibility of a stimulus whose contrast varies cyclically, alternating between light and dark. Age, refractive error, pupil and stimulus size, and retinal eccentricity all affect the outcome of contrast sensitivity testing. The values obtained are also dependent on the psychophysical technique used to determine sensitivity. Early studies of contrast sensitivity in patients with chronic simple glaucoma (CSG) and ocular hypertension (OHT) have demonstrated spatial and temporal sensitivity losses.