Planimetrically determined vertical cup/disc and rim width/disc diameter ratios and related factors

To evaluate the distribution and factors related to planimetrically determined vertical cup/disc (v-C/D) and rim width/disc diameter (Rw/Dd) ratios of the optic discs in a population-based study of Japanese subjects without glaucoma.

Of 4632 eligible residents 40 years of age and older, 3762 residents underwent a detailed ocular examination including sequential optic disc stereo photography with a digital nonmydriatic fundus camera. The photographs were assessed by computer-assisted planimetry. The authors studied both eyes of 2311 nonglaucomatous subjects and only one right (left) eye of 196 (175) subjects for whom disc stereo photographs were of acceptable quality.

The median (2.5th and/or 97.5th percentile) disc area, v-C/D, its asymmetry, and the superior- and inferior-minimal Rw/Dd ratios were 2.56 (1.68, 3.71) mm(2), 0.56 (0.70), 0.05 (0.14), 0.18 (0.10), and 0.21 (0.12), respectively. Multiple regression analysis showed that males had larger discs and superior Rw/Dd and smaller inferior Rw/Dd ratios. Increased age was correlated with increased v-C/D and decreased superior and inferior Rw/Dd ratios. Higher intraocular pressure (IOP) and thinner central corneal thickness (CCT) were correlated with higher v-C/D and smaller inferior rim/disc ratios, and lower diastolic ocular perfusion pressure (OPP) with greater v-C/D and smaller superior Rw/Dd ratios.

In nonglaucomatous eyes, increased v-C/D and decreased superior and inferior Rw/Dd ratios were significantly correlated not only with increased age and disc size but also with higher IOP, lower diastolic OPP, and thinner CCT, suggesting that these simple disc parameters also represent vulnerability to glaucoma insults in nonglaucomatous eyes.