Characteristics of the optic disc cup

The frequency distribution of the optic cup/optic disc ratio (CDR) and the optic cup depth (OCD) were investigated using clinical data. The mean CDR is 0.30 (SD = 0.13), and the mean OCD is 2.10 D (SD = 0.89 D). Seventy-four percent of 1352 eyes had a CDR of 0.3 or less, and 68% of 1168 eyes had an OCD of 2 D or less. The distribution of the CDR's differs from a normal distribution, but that of the OCD's is nearly normal.