Pentacam Scheimpflug tomography findings in topographically normal patients and subclinical keratoconus cases

To evaluate Pentacam ectasia detection indices in topographically normal patients and in subclinical keratoconus cases.

Prospective, observational case series.

setting: Institutional. patients: Group 1 comprised 1 eye from 189 patients with unremarkable topography and Groups 2 and 3 included the better and worse eyes, respectively, of 55 keratoconic patients. Group 2 eyes with normal topography (n = 37) were considered subclinical keratoconus cases. observation procedure: Pentacam Scheimpflug tomography. main outcome measures: Eleven Pentacam ectasia detection indices.

All Pentacam ectasia indices significantly differed between Groups 1 and 2 and were correlated with keratoconus grade. Only 99 eyes (52%) in Group 1 had normal values for every index, whereas 7 subclinical keratoconus eyes (19%) showed 2 or fewer abnormal indices. Standardized relational thickness and overall deviation indices had 73% and 89% sensitivity for subclinical keratoconus, respectively. Both average and maximum pachymetric progression indices offered 84% sensitivity while maximum relational thickness index showed 78% sensitivity for subclinical keratoconus. Optimized cutoff values for subclinical keratoconus increased the sensitivity of the standardized and maximum relational thickness indices.

Pentacam Scheimpflug tomography can detect most subclinical keratoconus cases with unremarkable topography, but performance is not as good as reported and varies considerably for each index. The overall deviation, average and maximum pachymetric progression, and maximum relational thickness indices offer the highest sensitivity, which can be improved by using optimized cutoff values. Specificity constitutes an issue for some indices and up to 10% of subclinical keratoconus cases may go undetected by this technology.