In eyes with normal fields, the cup/disc (C/D) ratio was found to be significantly related to applanation pressure PA level, ratio of pressure reading at the beginning of the tonogram and the tonographic estimate of aqueous outflow activity (Po/C), and C-value. The frequency of C/D > 0.3 increased significantly with the PA level and with the magnitude of the Po/C ratio. It increased also as the C-value became smaller. This relationship was independent of age or family history of glaucoma.
Armaly MF, Sayegh RE. The Cup/Disc RatioThe Findings of Tonometry and Tonography in the Normal Eye. Arch Ophthalmol. 1969;82(2):191-196. doi:10.1001/archopht.1969.00990020193008