Use of photographs for measuring cupping in the optic disc

Abstract

(1) Four cup : disc ratios were measured from photographs of optic discs: (a) Cv/Dv, the ratio of the vertical diameters of the cup and disc respectively; (b) Ch/Dh, the corresponding ratio for the horizontal diameters; (c) A c/Ad, the area of the cup divided by the area of the disc; (d) r/d, the narrowest part of the rim round the cup divided by the diameter of the disc. (2) A special method of photography is described for enhancing the colour contrast between the floor of the cup in an optic disc and the surrounding rim of healthy tissue; this results in an improvement in the reliability of measurement of the above ratios. (3) The ratios were examined for their ability to separate discs in eyes with full fields from those in eyes with glaucomatous field defects. Up to go per cent. of discs could be separated in this way, the best separation being achieved with the vertical diameter ratio, Cv/Dv.