Neural Losses Correlated With Visual Losses in Clinical Perimetry

Abstract

Abstract: : Purpose: The validity of clinical perimetry for evaluation of the pathology of glaucoma is based on correlated losses in retinal ganglion cells and visual sensitivity, but relationships between neural and visual losses are not precise. The purpose of the present study was to investigate the sources of imprecision in the neural-sensitivity relationship for standard clinical perimetry. Methods: Perimetry data, by behavioral testing, and retinal histology data were obtained from rhesus monkeys with significant visual field defects caused by experimental glaucoma. Ganglion cell densities were obtained from sections of retina that corresponded to perimetry test locations at 3x3 deg, 9x9 deg and 15x15 deg in each quadrant and at 4 additional nasal field locations. Perimetry sensitivity as a function of ganglion cell density at corresponding retina/visual field locations was analyzed. Results: In log-log coordinates, the relationship for visual sensitivity as a function of ganglion cell density was linear. Neural-sensitivity functions were unsystematic across subjects and the neural and sensitivity losses were often poorly correlated for a given subject. The imprecision of the general relationship was reduced by compensation for the effect of retinal eccentricity on the slope and intercept of the neural-sensitivity relationship, and for the variation in retinal ganglion cell density with eccentricity. Conclusions: With retinal eccentricity as a factor, the neural losses from glaucoma are predictable from visual sensitivity measurements by clinical perimetry. The relationships derived from experimental glaucoma in monkeys also accurately predict the rate of age-related losses of retinal ganglion cells in humans, based on the normative perimetry data for age-related reductions in visual sensitivity.

Keywords: perimetry • ganglion cells • animal model