The Disc-Macula Distance to Disc Diameter Ratio: A New Test for Confirming Optic Nerve Hypoplasia in Young Children

The disc-macula: disc diameter (DM:DD) ratio is the ratio of the horizontal distance between the center of the optic disc and the macula to the mean diameter of the optic disc, as evaluated from fundus photographs. The diagnosis of optic nerve hypoplasia may be difficult in cases in which the optic discs are slightly reduced in size, or when the double ring sign is absent and the condition is bilateral. The DM:DD ratio was calculated for six eyes of five children with ophthalmoscopically obvious optic nerve hypoplasia, 12 eyes of six children in whom the diagnosis of optic nerve hypoplasia was equivocal (but established by visual field examination and retinal red free photography), 13 eyes of eight children with optic atrophy, and 25 eyes of 17 children with normal optic discs. The DM:DD ratio was found to be significantly higher for both groups with optic nerve hypoplasia than for those with optic atrophy and the normal controls. For practical purposes, when the DM:DD ratio is greater than 3.0, the diagnosis of optic nerve hypoplasia should be seriously considered.