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Editor,—In the optic disc, all visual afference originating in the photoreceptors of more than 1000 mm2retina is concentrated on an area of about 2 mm2 to 3 mm2. The retinal ganglion cell axons are nowhere else so densely and tightly packed as in the optic nerve head. It explains the importance of the optic disc for anomalies and diseases of the optic nerve. Regarding the marked interindividual variability of the size of the optic disc,1 we undertook the present study to evaluate whether the dimensions of the optic disc are correlated with the length and weight of the whole body.
The study included 517 white subjects (243 women, 274 men) with a mean age of 46.6 (SD 13.0) years (range 8–87 years) and a mean refractive error of −0.91 (2.77) dioptres (range −24.0 to +7.0 dioptres). The subjects came to the eye hospital for diagnosis and treatment of glaucoma (n=244), or for diseases in the contralateral eye not included in the study (n=273). If both eyes had been examined, only one randomly selected eye per individual was considered for statistical analysis. For all subjects, colour stereo optic disc photographs had been taken. The diapositives were projected, the outlines of the optic disc were plotted on paper and morphometrically evaluated. The ocular and camera magnification was corrected according to the Littmann method taking into account the anterior corneal curvature and refractive error.2 3 Body length and body weight were additionally determined.
No statistically significant relation was found between area and diameters of the optic disc and length and weight of the whole body (p>0.50; Pearson’s correlation coefficient R2<0.0005) (Fig 1). The same held true when only eyes with a myopic refractive error of less than 4 dioptres were taken into account, or when we considered only eyes with a myopic and hyperopic refractive error of less than 4 dioptres, or eyes with a myopic and hyperopic refractive error of less than 2 dioptres. Dividing the total study group into women and men, both sexes differed significantly (p<0.0001; Mann–Whitney test) in body length and body weight. They did not vary significantly (p=0.45) in optic disc area (2.74 (SD 0.72) mm2 in women versus 2.80 (0.72) mm2 in men).
The results suggest that, in white people, the size of the optic disc is independent of the dimensions of the whole body. Although the Littmann method may underestimate optic disc measurements in myopic eyes,4 one may arrive at this conclusion, since the correlations between disc area and body length and weight also remained statistically insignificant when only eyes with minor refractive errors were taken into account. The result of this study corresponds with the finding that women and men, although varying in body length and weight, did not differ in optic disc area. It agrees with other morphometric studies in which women and men did not vary significantly in retinal surface area and number of retinal photoreceptors and optic nerve fibres while optic disc area was significantly correlated with the count of optic nerve fibres and retinal photoreceptors and retinal surface area.5 The finding of the present study that the size of the optic disc is independent of the dimensions of the whole body may be important for optic nerve anomalies and diseases, such as optic disc drusen and non-arteritic anterior ischaemic optic neuropathy, the frequencies of which are correlated with optic disc size.5
Supported by Deutsche Forschungsgemeinschaft (Klinische Forschergruppe “Glaukome", grant no Na 55/6–2).