An optimal reference plane to detect glaucomatous nerve fiber layer abnormalities with computerized image analysis

Nerve fiber layer height measured with respect to a standardized retinal reference plane is diminished by glaucoma. The definition of the reference plane influences the nerve fiber layer measurements. We empirically determined the best reference plane for measurement of nerve fiber layer height. Optimal parameters for measurement reproducibility were determined for a group of 6 normal and 6 glaucomatous eyes each imaged nine times. Optimal ability to distinguish normal from glaucomatous eyes was determined for a group of 33 normal eyes and 36 glaucomatous eyes each imaged once. Measurements with the smallest variability (root mean square error = 32 gm) and the highest sensitivity (83%) and specificity (88%) were achieved when the reference plane is defined by portions of the image from a peripheral temporal area 32° wide, and for two peripheral nasal areas of 55° width centered 30° above and below horizontal. These parameters for the definition of the reference plane should provide measurements of nerve fiber layer height with the least variability and the greatest ability to discriminate between eyes with early glaucomatous damage and normal eyes.