Variability of the real dimensions of normal human optic discs.

Using Littmann's method for correcting the magnification of central fundus photographs, we evaluated planimetrically the color slides of 88 unselected optic discs without evidence of any optic nerve disease. High myopes (less than -8.00 diopters) had been excluded. Mean optic disc area measured 2.89 +/- 0.76 mm2 (minimum 0.86 mm2, maximum 5.39 mm2), mean cup area 0.63 +/- 0.64 mm2 (minimum 0.00 mm2, maximum 3.10 mm2) and mean neuroretinal rim area 2.26 +/- 0.58 mm2 (minimum 0.86 mm2, maximum 3.84 mm2). Horizontal disc diameter ranged from 0.91 mm to 2.42 mm (mean 1.79 +/- 0.27 mm) and vertical diameter from 1.08 mm to 2.76 mm (mean 1.97 +/- 0.29 mm). Coefficients of variation of the method's reproducibility were 0.03 for intraobserver and 0.03 for interobserver determination. Regarding the Gaussian distribution curve based on these preliminary data, microdiscs can be defined as being smaller than 1.4 mm2 (mean minus two standard deviations) and macrodiscs as being larger than 4.4 mm2 (mean plus two standard deviations).