Comparison of specular microscopy and ultrasound pachymetry before and after cataract surgery

To compare specular microscopy (Topcon SP-3000P, Topcon Corporation, Tokyo, Japan) and ultrasound (US) technology when evaluating central corneal thickness (CCT) prior to and after phacoemulsification. Corneal edema was assessed in phacoemulsification patients due to senile cataract by measuring CCT preoperatively and 1 day, 1 month, and 3 months postoperatively. Bland-Altman analysis was performed to assess interchangeability between pachymetry techniques for each visit. Repeated measures analysis of variance was performed to evaluate variation in CCT agreement depending on the degree of corneal edema. One hundred and eighteen patients aged 73.9 +/- 10.1 years were recruited. Topcon SP-3000P provided significant (p < 0.0001) lower CCT values than US with and without induced corneal edema. Mean differences between CCT techniques for baseline, 1 day, 1 month and 3 months after cataract surgery were -28.9 +/- 22.6, -30.5 +/- 41.4, -32.3 +/- 16.2 and -33.0 +/- 16.9 mu m, respectively. The systematic bias observed was not significantly different among the 4 visits (p = 0.59). The estimated limits of agreement (based on 1.96 standard deviation) were substantial, being 90.5, 165.8, 64.9 and 67.5 um at baseline, 1 day and 1 and 3 months. Topcon SP-3000P provides similar systematic bias in comparison with US technique for CCT measurements regardless of the degree of corneal edema after phacoemulsification, which should be reduced after applying a constant calibration adjustment of similar to 30 mu m. However, interchangeability between techniques may be still limited by the notable random measurement error.