Intrasubject corneal thickness asymmetry

PURPOSE: To establish the normal distribution for intrasubject (right eye/left eye) central corneal pachymetry in a refractive surgery population. METHODS: A retrospective analysis was performed on 1448 eyes of 724 consecutive patients evaluated for refractive surgery. Pachymetric data were obtained from the Pentacam Eye Scanner. Right and left eye pachymetry values were compared for the corneal apex, pupil center, and thinnest point. Statistical analysis was performed to determine normal levels of variance. RESULTS: The average apex reading was 539.3±36.8 μm, median 542 μm, and mode 539 μm (range: 411 to 664 μm). Values for the pupil center (average 538.7 μm) and thinnest point (average 536.1 μm) followed a similar distribution. The average pachymetry difference between fellow eyes was 8.8±7.2 μm at the apex, 8.9±8.3 μm at the pupil center, and 9.0±8.3 μm at the thinnest region. CONCLUSIONS: Individuals with a greater than 23.2 μm apical pachymetry difference represent less than 5% of the population. Individuals with an apical difference greater than 30.4 μm represent less than 0.5%. Pachymetric asymmetry outside the normal range should alert the clinician to examine for other parameters that are more established refractive surgery risk factors.