Repeatability of Central Corneal Thickness Measures by Orbscan Pachymetry for Right and Left Eyes

Objectives: To assess the repeatability of Orbscan measures on right versus left eyes. Methods: Three Orbscan measures were taken from the right eye and then the left eye by the same operator on 50 healthy myopic subjects (average right eye = -4.3 DS) aged 19 to 58 years, half of whom were successful long-term soft contact lens (SCL) wearers. The central point thickness measurement was compared for the 3 scans for each eye, the variability calculated based on the coefficient of variation (COV) and also paired comparisons with limits of agreement. No acoustic factor was applied. Results: Single central point thickness values ranged from 0.483 to 0.663 mm. with mean values of 0.579 mm for both eyes, with no statistically significant difference between spectacle wearers and SCL wearers (P >= 0.387). From 3 repeat scans, the net difference was -0.001 mm between third and first scans of right eyes and +0.001 min for left eyes (P >= 0.5). Overall, the COV was close to 1%, being marginally higher (0.955% and 1.176%) in spectacle wearers than SCL wearers (0.922% and 0.836%; P, NS). However, an overall assessment of the COV data indicates that the values were inversely related to absolute thickness values, being slightly higher for thinner versus thicker comeas (P <= 0.01). The limits of agreement (95% confidence interval) between repeat sets of measures were 0.018 mm for third versus first scans of either eye or 0.023 mm for first scans of right versus left eyes. Conclusions: The results confirm excellent repeatability of Orbscan pachymetry measures in both spectacle and contact lens wearers. For the adult subjects assessed, there was no evidence of a right/left eye difference and/or a progressive change in measured thickness with time. The high similarity between right and left eye measures should be taken into account if data from both eyes are being used either in contralateral eye comparisons or in comparative Studies of different pachymeters.