Measurement of retinal nerve fiber layer thickness and its functional correlations with the visual field

We have developed a technique for stereophotogrammetric measurements of retinal nerve fiber layer thickness at the disc margin. This technique has a reproducibility ranging from 3.9% to 6.0% in normal, ocular hypertensive and high pressure open angle glaucomatous eyes. The presence of a halo or scleral crescent had no effect on the reproducibility of the measurements. The measurements have shown that ocular hypertensive eyes have about an 18% decrease of retinal nerve fiber layer thickness compared to normals. High pressure open angle glaucomatous eyes have about a 43% decrease in retinal nerve fiber layer thickness compared to normals. This technique allows the development of maps of retinal nerve fiber layer thickness so that localized changes at the disc margin can be detected. The thinnest nerve fiber layer occurs primarily in the temporal segment. This technique has also correlated measurements of nerve fiber layer thickness with other measurements of the optic disc, particularly showing a significant correlation with area of pallor as well as measurements of the width of optic disc cup at about halfway between surface and the bottom of the cup. A significant correlation with visual field loss has been shown in high pressure open angle glaucomatous eyes, primarily with the temporal quadrant of the retinal nerve fiber layer and the nasal visual field. The rate of the visual field change in primary open angle glaucoma has been correlated with the initial nerve fiber layer thickness, with the greater the retinal nerve fiber layer thickness the greater the rate of the visual field loss during follow-up. These findings suggest that retinal nerve fiber layer thickness discriminates between normal, ocular hypertensive eyes as well as those with open angle glaucomas and may be useful in following patients with open angle glaucoma prior to development of the visual field loss.