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March 2002

How Big Is Small?

Arch Ophthalmol. 2002;120(3):406. doi:

In reply

As mentioned in our report, the vast majority of optic discs affected by nonarteritic anterior ischemic optic neuropathy (AION), along with the fellow unaffected nerves, have small cup-disc ratios. In 1974, Hayreh1 found no physiologic cup in 9 of 10 normal fellow eyes in patients with AION. Beck et al2 found that 37 of 51 fellow eyes had no cup, 7 had cup-disc ratios of 0.1, 4 of 0.2, 2 of 0.3, and 1 of 0.4. Felt et al3 noted similar findings. In their report, 14 of 30 patients, but only 2 of 29 controls, had cup-disc ratios of 0.1 or less. In all the above cases, cup-disc ratios and comments regarding optic disc structure were based on photographic evaluation and, in some cases, Hruby lens examination. The designation "disc at risk" is therefore a clinical one connoting small cup-disc ratio. Indeed, Bengtsson4 found a close association between cup-disc ratio and optic disc diameter. Thus, most optic nerves involved by AION with small cup-disc ratios are presumed to be small. Such "small" optic discs are thought to have crowding of axons as they pass through the lamina cribrosa, making such axons susceptible to ischemia. Precise quantification of optic disc diameter or information regarding the cause of the "disc at risk" is of interest but superfluous in the clinical setting.

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