Simple photogrammetric diagnosis of optic nerve hypoplasia.

It is often clinically important, but also often difficult, to make a definitive morphologic diagnosis of optic nerve hypoplasia in a young child. If, however, one can obtain a photograph of the fundus, including the optic disc, one can make a simple measurement of the horizontal diameter of the optic disc and make this diagnosis. To determine if the horizontal diameter of the optic disc on a 35-mm photographic transparency could be used to separate patients with optic nerve hypoplasia from normal individuals, I measured directly on the transparency the horizontal diameter of the optic disc image taken by a standard 30 degrees field fundus camera with X2.5 magnification in a series of 55 normal eyes, and in 16 eyes with clinically confirmed optic nerve hypoplasia. For the normal series of eyes, the mean optic disc horizontal image diameter was 3.88 mm, with a range of 3.44 to 4.70 mm. For the series of eyes with optic nerve hypoplasia, the mean horizontal diameter was 2.64 mm, with a range of 1.80 to 3.27 mm. There was no overlap between the normal control series and the pathologic series. In subjects with no major ametropia (less than 2.5 diopters of spherical or cylindrical refractive error), a 3.4-mm horizontal diameter optic disc image on a 35-mm transparency can be used as a clinical guide or dividing line for the diagnosis of optic nerve hypoplasia, larger nerves being considered normal and smaller nerves being considered hypoplastic.