The performance of optic disc-macula distance to disc-diameter ratio in qualitative and quantitative assessment of the optic disc size.

OBJECTIVES

We aimed to evaluate the performance of the optic disc-macula distance to disc-diameter ratio (DM/DD) in qualitative and quantitative assessment of optic disc size.

METHODS

In 300 apparently normal eyes, we determined the correlation between DM/DD and the planimetric disc area (DA) and evaluated the performance of DM/DD in discriminating between small and large discs. The ability of DM/DD to predict the actual DA was validated in a separate cohort of 200 eyes. The disc size in eyes with glaucoma or related diseases was compared with DA- or DM/DD-based disc size.

RESULTS

The DM/DD and its square of inverse (DD2/DM2) showed excellent non-linear and linear correlations, respectively, with DA (p < 0.001 and p < 0.001, respectively), demonstrating their performance in discriminating between small (<2.04 mm2) and large (>2.94 mm2) disc sizes with an area under the receiver operating characteristic curve of 0.901 and 0.959, respectively. The difference between the predicted DA and planimetric DA was within ±10% in more than 80% of the eyes. Eyes with suspected and normal-tension glaucoma exhibited larger discs (p < 0.01) when evaluated using both DM/DD and DA. The variation in disc-macula distance seemed to be a confounding factor for DM/DD in inferring the precise disc size.

CONCLUSION

DM/DD, which can be easily calculated from various kinds of fundus photographs or images, was an excellent and interchangeable tool for qualitative and quantitative assessment of disc size, which did not require correction for ocular magnification.