Positions of Ocular Geometrical and Visual Axes in Brazilian, Chinese and Italian Populations

Purpose: To identify the relative positions of geometrical and visual axes of the eye and present a method to locate the visual center when the geometrical axis is taken as a reference.Methods: Topography elevation data was collected using a Pentacam HR (R) topographer from 2040 normal eyes of 1020 healthy participants in Brazil, China and Italy. A three-dimensional, rotation algorithm, a first-order Zernike polynomial fit and a nonlinear least-squares error function was used within an optimization function to locate the geometrical axis and the visual center of each eye.Results: The right eyes of participants were significantly more tilted than left eyes throughout the topography scanning process (p<0.001). The visual centers were always located in the nasal-superior quadrant, although the visual centers of fellow eyes were not symmetrically located. Mean distances between the visual center and the geometrical center in right eyes were 0.80.29mm, 0.56 +/- 0.18mm and 0.91 +/- 0.34mm among Brazilian, Chinese and Italian participants, respectively, and located at angular positions of 38.7 +/- 24.5 degrees, 23.0 +/- 29.8 degrees and 23.1 +/- 28.1 degrees from the nasal side. However, in left eyes, mean distances were 0.76 +/- 0.33mm, 0.45 +/- 0.12mm and 0.75 +/- 0.33mm at polar angles from the nasal side of 59.3 +/- 29.0 degrees, 50.6 +/- 44.5 degrees and 61.8 +/- 34.1 degrees, respectively.Conclusions: Fellow eyes do not perform similarly during the fixation process, with right eyes tending to tilt more than left eyes, and the visual centers of the fellow eyes positioned differently relative to the geometrical centers.