Interocular differences of the Pentacam measurements in normal subjects

The aim of this study was to determine the interocular differences of the Pentacam corneal measurements in a normal population.

A retrospective analysis was performed on 550 eyes of 275 consecutive subjects evaluated for refractive surgery at the Rassoul Akram Hospital, Iran University of Medical Sciences. A Pentacam Scheimpflug camera was used for corneal measurements. Statistical analysis was performed to determine the normal levels of the difference between the two eyes.

One hundred and four men and 171 women with a mean age of 29.1 +/- 7.73 years were evaluated. The mean (range) interocular difference was 2.17 (zero to 21) microm for maximum anterior elevation (AEmax), 3.62 (zero to 31) microm for maximum posterior elevation (PEmax), 8.42 (zero to 30) microm for minimum corneal thickness (CTmin), 0.06 (zero to 0.4) mm(3) for three millimetre corneal volume (CV3), 0.19 (zero to 1.2) mm(3) for five millimetre corneal volume (CV5), 0.44 (zero to 2.9) mm(3) for seven millimetre corneal volume (CV7), 0.24 (zero to 2.5) dioptres for the mean keratometry (Km) and 0.39 (zero to 2.5) D for measurements of the corneal dioptric power in the steepest meridian (Kmax).

Individuals with differences greater than 17.4 microm in AEmax, 29.1 microm in PEmax, 29.6 microm in CTmin, 2 D in Km, 2.27 D in Kmax, 0.32 in CV3, 1.05 in CV5, and 2.6 in CV7 between eyes represent less than 0.5 per cent of the population. An interocular difference outside the normal range should alert the clinician to examine for other parameters that are more predictive of post-refractive surgical ectasia.