Pentacam vs SP3000P specular microscopy in measuring corneal thickness

• Oculus Pentacam measures significantly thicker corneas compared with specular microscopy.
• There was a good linear correlation between the values obtained with these two devices.
• A regression formula that could make the results obtained with these machines comparable was found.

PurposeTo compare corneal thickness (CT) measurements obtained with SP3000P specular microscope and Pentacam in eyes screened to undergo refractive surgery (RS).MethodsIn this prospective study, a non-randomized consecutive series of 73 healthy eyes (age range: 14–78 years; mean = 38.4 ± 14.9) underwent CT measurement with both Oculus Pentacam and Topcon SP3000P specular microscope to assess their suitability to undergo corneal RS.ResultsCT measurements with SP3000P ranged from 451 to 609 μs (mean 523.1 ± 34.4 μs). The measurements obtained with Pentacam ranged at the corneal apex from 477 to 672 μs (mean 558.9 ± 38.9 μs), at the pupil center from 477 to 672 μs (mean 557.9 ± 38.9 μs) and at the thinnest point from 474 to 669 μs (mean 551.1 ± 39.4 μs). CT measurements showed a good correlation but a statistically significant difference at the pupil center (mean −34.9 ± 14.6 μs, R2 = 0.860, p < 0.001), at the apex (mean −35.9 ± 14.9 μs, R2 = 0.856, p < 0.001) and at the thinnest point (mean −32 ± 14.8 μs, R2 = 0.862, p < 0.001). The calculated regression formulas were: y = 0.816x + 66.94 for the apex, y = 0.819x + 66.07 for the pupil center and y = 0.810x + 73.13 for the thinnest point; where y is the CT measured with the SP3000P and x is the measurement obtained with the Oculus Pentacam.ConclusionsOur results suggest that SP3000P measures thinner corneas compared to the Pentacam and that the correcting factor we identified should be applied to make comparisons between these two devices.