Comparison of central corneal thickness as measured by non-contact specular microscopy and ultrasound pachymetry before and post LASIK.

PURPOSE

To compare central corneal thickness (CCT) measurements made by ultrasound pachymetry and non-contact specular microscopy in eyes before and post laser in situ keratomileusis (LASIK).

METHODS

Forty eyes of 20 consecutive refractive surgery candidates were included in this study. The CCT in both eyes was measured before and 3 months after LASIK with a non-contact specular microscope and a ultrasound pachymeter.

RESULT

Both before and after LASIK, the difference of the mean CCT between non-contact specular microscopy and ultrasound pachymetry was statistically significant (P < 0.001 before surgery, and P = 0.02 after surgery). The difference between them was -14.41 microm and -3.69 microm, respectively. In both situations, non-contact specular microscopy and ultrasound pachymetry measurements were highly correlated (r = 0.959, before surgery, and r = 0.979 after LASIK). Bland-Altman analysis showed that either before or post LASIK, the 95% limits of agreement have a span of approximately 30 microm. Preoperatively, the mean standard deviation of repeated measurements was 4.26 microm by ultrasound pachymetry, and 4.02 microm by non-contact specular microscopy, whereas it was 3.83 microm by ultrasound pachymetry, and 3.89 microm by non-contact specular microscopy, postoperatively. No statistically significant differences were found between the mean standard deviations by these two devices in both situations (P = 0.561 before surgery, and P = 0.849 after LASIK).

CONCLUSIONS

Both before and after LASIK, non-contact specular microscopy is not in complete agreement with ultrasound pachymetry in measuring CCT. Both devices provided comparable repeatability of measurements.