RESUMO
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 µm, group 2 (81 eyes) with TCT between 523 and 564 µm, while group 3 (40 eyes) enrolled TCT >564 µm. 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.
RESUMO
PURPOSE: To assess the effect of age on elevation and pachymetric Pentacam keratoconus (KC) detection indices, and the need to adjust normative values accordingly. METHODS: In a retrospective study, 95 eyes of myopic normal subjects without KC were evaluated using the OCULUS Pentacam, with an age range of 17.4 to 46.8 years. Subjects were categorised into three groups according to their age: the first included those younger than 21 years (19 eyes), the second was for the age range of 21-40 years (65 eyes), and the third comprised subjects older than 40 years (11 eyes). RESULTS: There were statistically significant differences among the three groups regarding many elevation indices: AE from BFS, PE from BFS, and PE minus AE from BFS (P = 0.003, 0.010, and <0.001, resp.), and pachymetric indices: PPI avg, PPI max, ART avg, ART max, and diagonal decentration of the thinnest point (P = <0.001, 0.024, 0.003, 0.026, and 0.026, resp.). On comparing subjects below 21 years to those above 40 years, there was a statistically significant decrease of both PE from BFS and PE minus AE (P = 0.005 and <0.001, resp.) and statistically significant increase in AE from BFS (P = 0.001). CONCLUSIONS: Age is an important determinant of elevation indices, significantly altering their normative values. The use of the more robust pachymetry, rather than elevation, indices is recommended in subjects below 21 or above 40 years of age.
