Pentacam HR criteria for curvature change in keratoconus and postoperative LASIK ectasia

To determine criteria for keratoconus or postoperative LASIK ectasia progression or improvement based on Pentacam HR (Oculus Optikgeräte GmbH) measured steepest corneal curvature.

Sixty-one eyes from 41 patients with keratoconus or postoperative LASIK ectasia were evaluated. Each eye was measured 5 times with the Pentacam HR during the same clinic visit and the random measurement variations of Rmin(back) and maximal keratometry (Kmax; mathematically linked to Rmin[front]) were statistically analyzed. Confidence levels for diagnosing true curvature change were determined for 3 typical clinical situations differing by the number of available Pentacam measurements.

With a single past and single present Pentacam HR measurement available (situation 1+1), the 95% confidence levels of true change for ΔKmax, ΔRmin(front), and ΔRmin(back) were 1.51 diopters (D), 0.162 mm, and 0.290 mm, respectively. With one prior and the average of five present Pentacam measurements (situation 5+1), the 95% confidence levels of true change for ΔKmax, ΔRmin(front), and ΔRmin(back) were 1.17 D, 0.126 mm, and 0.225 mm, respectively. With the average of five past and five present measurements (situation 5+5), the 95% confidence levels of true change for ΔKmax, ΔRmin(front), and ΔRmin(back) were 0.68 D, 0.072 mm, and 0.130 mm, respectively.

Steepest corneal curvature changed with 95% confidence if the difference between single past and present Kmax exceeded 1.51 D. With the advantage of five past and five present measurements, 95% confidence of real Kmax change occurs at a 0.68-D difference.