Pentacam HR Indices Variation in Normal Corneas with Different Corneal Thickness.

Purpose: To evaluate the effect of variable corneal thickness on Pentacam HR diagnostic indices in normal corneas.

Methods: Retrospective study was conducted at Al Watany Eye Hospital, Cairo, Egypt. Consecutive 160 eyes of young myopic subjects without KC were evaluated using Pentacam HR (WaveLight Allegro Oculyzer II, Erlangen, Germany). The elevation- and thickness-based indices were recorded. Enrolled corneas were categorized into three groups according to TCT quartiles; group 1 (39 eyes) included corneas with TCT <523  µ m, group 2 (81 eyes) with TCT between 523 and 564  µ m, while group 3 (40 eyes) enrolled TCT >564  µ m. The possible effect of pachymetry on Pentacam HR indices was assessed using partial correlation tests.

Results: In normal corneas, back elevation from best fit sphere (BE from BFS) and that from best fit toric ellipsoid (BFTE) were the elevation indices that showed statistically significant differences among groups ( P =0.013 and 0.019, respectively). Regarding pachymetric indices, maximum pachymetry progression index (PPI max) showed statistical significance ( P =0.001). Partial correlations, after excluding age and refractive error effects, showed that TCT was correlated with BE from BFS, BE from BFTE, and PPI max ( P =0.001, 0.001,0.002, respectively).

Conclusions: Some Pentacam HR indices varied with different corneal thickness in normal corneas. This necessitates inclusion of pachymetric subgroups in the normative database. The use of the more robust indices (average pachymetry progression index and front elevations) is recommended in relatively thin or thick corneas.