cup-disc ratio

ratio, cup-disc (C/D) 

The ratio of the horizontal diameter of the physiological cup to that of the horizontal diameter of the optic disc. It should be less than 0.5. If it exceeds that value, or if there is a difference in ratio between the two eyes, or if there is a progressive enlargement of the cup, glaucoma may be suspected (Fig. R1). See glaucomatous cup." >Fig. R1 Diagram of the physiological cup with a cup-disc ratio of 0