International Values of Central Pachymetry in Normal Subjects by Rotating Scheimpflug Camera.

Purpose: In corneal refractive surgery, postoperative ectasia risk assessment routinely includes pachymetric analysis at the apex and thinnest point. We examined whether these data differ worldwide and constructed preliminary country-specific normative thresholds.

Design: This was a multicenter, cross-sectional study.

Methods: Using the Pentacam Eye Scanner (OCULUS GmbH, Wetzlar, Germany), we examined 1 randomly selected eye from each of 555 normal adults (8 countries, 6 continents), measuring the thinnest point location, central pachymetry (thinnest point, pupillary center, and apex), and the apex-thinnest point difference. International differences were assessed by 1-way analysis of variance. Normative thresholds were defined by 2- and 3-SD gates or Tukey method.

Results: The thinnest point averaged 0.44 mm temporal and 0.29 mm inferior to the apex. Individual thinnest points located more than 1.0 mm inferior represented fewer than 0.5% of normal corneas (>0.76 mm in the US subgroup). The mean thinnest-point pachymetry was 536 μm overall, and values less than 469 or 435 μm (-2 or -3 SD, respectively) would be expected in less than 2.5% or 0.15% of normal corneas, respectively. The thinnest-point pachymetry averaged 2 to 3 μm thinner than apical (range, 0-32 μm). Differences of greater than 8.5 μm would be expected in less than 0.5% of normal corneas overall.

Conclusions: International differences were largely clinically insignificant. Nevertheless, it remains preferable to establish racial/geographic-specific normative values. We defined preliminary generalized and country-specific thresholds useful to the corneal refractive surgeon for identifying potentially abnormal corneas based on common pachymetric parameters, particularly the thinnest point by tomography.