Determination of the Location of the Fovea on the Fundus

PURPOSE: To evaluate whether the distance between optic nerve head and fovea in healthy eyes determined by scanning laser ophthalmoscope may facilitate estimation of the location of the fovea relative to the optic disc in patients with macular disease. METHODS: The angular distance was measured, in horizontal and vertical directions, between the center of the optic nerve head and the fovea in 104 eyes of 104 healthy probands. For additional evaluation of intraindividual variation in 70 of these persons the contralateral eye was measured as well. RESULTS: The distance between the optic disc and the fovea differed vertically more than horizontally (-1.5 +/- 0.9 degrees -3.65 to +0.65 degrees vs. 15.5 +/- 1.1 degrees 13.0-17.9 degrees ). There was a mean angle between the fovea and the center of the optic disc versus the horizon of -5.6 +/- 3.3 degrees. The intraindividual difference between right and left eyes was markedly lower, with average angles being 0.2 +/- 1.3 degrees vertically and 0.0 +/- 1.1 degrees horizontally. CONCLUSIONS: The distance between the optic nerve head and the fovea does not allow for a meaningful determination of the location of the fovea in eyes in which morphologic changes have occurred. The angle of rotation of the fovea relatively to the center of the optic nerve head is relatively stable. Therefore, the size of a central scotoma can be determined by movement of the blind spot according to the change of the preferred retinal locus (PRL). In addition, the knowledge of the location of the fovea enables determination of the position in the contralateral eye of the same patient.