PERIMETRY AND CLINICAL PSYCHOPHYSICS IN GLAUCOMA

Emanuel Hospital And Health Center, Portland OR

Investigators

Linked publications & trials

Abstract

DESCRIPTION (from abstract): Glaucoma is one of the leading causes of blindness. Approximately 2 million people in the United States have glaucoma, and another 3 to 6 million people, including 4-8 percent of the population over age 40, are at risk of developing glaucoma because of elevated intraocular pressure. The ability to detect the earliest signs of glaucomatous damage to the optic nerve is important for effective clinical decision-making concerning treatment intervention. In order to improve early detection, an understanding of the nature of early glaucomatous damage to the optic nerve is essential. This project tests three competing hypotheses concerning the basis of early glaucomatous damage: (1) that there is a selective loss of large diameter optic nerve fibers; (2) that the earliest glaucomatous damage is specific to a group of nerve fibers that terminate in the magnocellular layers of the lateral geniculate nucleus (M-cells); or (3) that nerve fiber losses in glaucoma are not specific to particular fiber pathways or sizes, but are most readily noticed for visual functions that are subserved by nerve fibers that have minimal redundancy or receptive field coverage. The three hypotheses will be tested by longitudinally evaluating a variety of visual functions throughout the visual field of moderate and high risk ocular hypertensives and patients with early glaucomatous visual field loss. The visual functions will include conventional automated perimetry, short wavelength automated perimetry (SWAP), resolution perimetry, high frequency flicker perimetry, and frequency doubling perimetry. These functions are thought to be mediated by ganglion cells with different functional properties, fiber sizes and amounts of coverage or redundancy. By examining the extent of neural damage and changes over time in the various visual functions, it will be possible to determine the validity of the three hypotheses. The outcome of this work will provide both a theoretical and an empirical basis for the development of new screening procedures for glaucoma. This project will also assess the relation between early losses of visual function in glaucoma and structural changes to the optic nerve head. Quantitative measures of optic disc topography will be obtained, using infrared raster stereography with the Glaucoma-Scope and confocal scanning laser ophthalmoscopy with the Heidelberg Retina Tomograph. Together with evaluations of visual function, these optic disc topography measures will permit the relationship between structural and functional losses to be determined for early glaucomatous damage.