Optic nerve hypoplasia: papillary diameter and clinical correlation.

Hypoplasia of the optic nerve is often subtle, and reduction in papillary diameter can be difficult to detect during ophthalmoscopic examination. Using a slit-lamp and a posterior fundus contact lens, we evaluated papillary diameter by bringing margins of the light beam to coincide with the limits of the optic nerve head. The method was standardized with 140 presumably normal eyes. Then we studied 17 consecutive eyes showing optic nerve hypoplasia. Hypoplasic discs were separated into two categories: (1) nine cases defined as having "moderate" hypoplasia, in which average disc diameters ranged between -2 and -2.5 standard deviations under the mean normal value; and (2) eight eyes with "severe" hypoplasia, showing average disc diameters less than the normal mean value by 2.5 standard deviations or more. Double peripapillary ring sign and low disc/artery ratio are clues often used in the diagnosis of optic nerve hypoplasia. The incidence of these signs was also evaluated in the hypoplasic discs studies. The double ring sign was present in two of the nine eyes with moderate hypoplasia, and in seven of the eight eyes with severe hypoplasia. Of eight eyes with moderate hypoplasia, only one showed a disc/artery ratio inferior to the mean normal value -2 standard deviations, whereas this ratio was significantly reduced in all cases of severe hypoplasia. These ophthalmoscopic clues therefore appear to be much less valuable than direct measurement of the optic disc for detecting a subtle reduction in disc diameter. This is of particular interest when one considers that all the nine eyes with moderate hypoplasia had alteration in visual function upon presentation.(ABSTRACT TRUNCATED AT 250 WORDS)