Disc-to-macula distance to disc-diameter ratio for optic disc size estimation

Purpose: To investigate the usefulness of the parameter of disc-to-macula distance (DM) to disc-diameter (DD) ratio in estimating optic disc size. Patients and Methods: A total of 88 normal subjects, 18 subjects with physiological macrodiscs, and 16 early glaucomatous patients were recruited for the study. The DM, which is the horizontal distance between the center of the optic disc and the macula, and DD were determined by planimetry. Results: No significant differences in DM were observed among the three groups (P = 0.12). The DM:DD ratios were significantly lower (P < 0.0001) in subjects with physiological macrodiscs (1.91 +/- 0.07) compared with normal subjects (2.54 +/- 0.13) and glaucomatous patients (2.50 +/- 0.15). No correlation between the DM:DD ratios and refractive error was found (P = 0.10). Conclusions: The DM:DD ratio can be taken as a relative size unit for the optic disc. In particular, the ratio may be clinically useful in the identification of macrodiscs.