There is considerable individual variation in the susceptibility of the optic nerve to damage from glaucoma. High intraocular pressure is an important risk factor, but its measurement cannot be used to reliably predict which patients will develop visual loss. Computerized threshold perimetry has increased the consistency with which reliable visual field data can be obtained. Still, perimetry remains a subjective test which may detect abnormalities only after significant optic nerve damage has occurred. There is considerable clinical and histological evidence that damage to the optic nerve head precedes measurable visual field loss. Sensitive, objective measures are required to detect glaucomatous optic nerve damage before functional loss occurs, and to provide an accurate barometer of the success or failure of treatment. This prospective longitudinal clinical study uses quantitative measurements of the surface contour of the optic nerve head and peripapillary nerve fiber layer to test the hypotheses that: 1) structural changes of the optic nerve head and nerve fiber layer precede visual field loss in subjects at risk for developing glaucoma, and 2) quantitative measurements of the optic nerve head and nerve fiber layer are more sensitive than measurements of the visual field to document progressive glaucomatous damage in patients with early glaucoma. Simultaneous stereoscopic videographic image acquisition (Rodenstock Analyzer) and computerized digital image processing will generate the quantitative measurements. To test the above hypotheses effectively, additional objectives of the proposed work are to 1) implement hardware changes in the image acquisition system to increase image and measurement resolution; 2) develop methods of image processing to increase the accuracy and decrease the variability of measurements; 3) develop new structural parameters which more closely reflect the number of retinal ganglion cell axons in an eye; 4) prospectively measure the effects of aging on the structure of the optic nerve and peripapillary nerve fiber layer in a group of age-matched normal controls, and 5) define the clinical utility of computerized image analysis of the optic nerve head and nerve fiber layer by comparison with clinical techniques.
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