Novel pachometry calibration

The purpose of this study was to develop a simple method for cross-calibrating instruments that measure corneal thickness.

Fourteen rigid lenses of different thicknesses were manufactured using a material with refractive index of 1.376. Center thickness of the lenses (CT) was measured using a computerized optical pachometer (OP), two optical coherence tomographers (OCTs), and a confocal microscope (CM). Accuracy of measurements was compared between the four instruments.

Before calibrating the machines, there was a significant effect of the measurement device (p < 0.05). The differences between instruments were eliminated (p > 0.05) after applying calibration equations for each device. In addition, after each instrument was calibrated with lenses of 1.376 refractive index, there was no significant difference (p > 0.05) between measured values of lens center thickness by OP, each OCT, CM, and the physical center thickness of the lenses.

Using calibration lenses with the same refractive index as the cornea (1.376) allows rapid and simple calibration of the pachometers so that corneal thickness measurements from different devices can be used interchangeably.