Position of the fovea centralis with respect to the optic nerve head

Examination of the ocular fundus via indirect ophthalmoscopy gives the clinician an impression of foveal position relative to the nerve head. In some patients, the fovea appears to be in an unusual position (i.e., ectopic): it may appear to be higher or lower than expected, or closer to or farther from the nerve head. There is little published quantitative information on this subject. The purpose of this study was to examine foveal position in a group of normal adult eyes, so that clinicians and other researchers will be able to determine on a more objective basis whether or not a given patient shows foveal ectopia. Using ocular fundus photographs for 446 normal adult eyes, we found the foveal center to be, on average, 6.11 degrees +/- 3.32 degrees below a horizontal line bisecting the nerve head. For a smaller sample of 66 eyes, we found the average distance between the nerve head and foveal centers to be 4.93 +/- 0.33 mm (right eye) and 4.88 +/- 0.36 mm (left eye). Correlations of these data for right and left eyes are also examined. Nerve head data for the group of 66 right eyes were also analyzed to yield dimensions of a best-fitting ellipse: the mean minor axis was 1.75 +/- 0.2 mm; the mean major axis 1.95 +/- 0.2 mm. Ectopia (heterotopia) of the fovea has been found in association with chorioretinitis, fibrous traction bands, and/or colobomas of the choroid and optic nerve (including anomalous insertion of the optic nerve), microcephalus, and microphthalmia. A number of separate cases with anomalous nerve heads and/or foveal positions are discussed in this paper.(ABSTRACT TRUNCATED AT 250 WORDS)