Analyzing small-incision cataract surgery by Orbscan II fourth-dimensional pachymetry mapping

To assess the changes in pachymetry after routine corneal and scleral tunnel phacoemulsification.

Discipline of Ophthalmology, University of Auckland, Auckland, New Zealand.

This prospective study comprised 174 eyes of 174 consecutive patients having uneventful, small-incision, sutureless, phacoemulsification cataract surgery; 124 patients had a clear corneal incision and 50, a superior scleral tunnel incision. Difference pachymetry maps were derived from Orbscan II elevation topography data obtained before and 4 weeks after surgery. Corneal thickness changes at 12 midperipheral areas located in 12 meridians were derived from difference (subtraction) maps. The mean corneal thickness within a single area corresponding to the center of the surgical incision was compared to the mean pachymetry readings of all 12 midperipheral measurements.

The overall mean midperipheral corneal thickness (12 samples per cornea) increased by a mean of 5.89 microm +/- 16.09 (SD) in the clear corneal incision group and 6.89 +/- 14.50 microm in the scleral tunnel group. The mean central corneal thickness increased by 7.28 +/- 20.98 microm and 7.74 +/- 21.34 microm, respectively. The corneal thickness in the meridian closest to the incision was significantly higher than the mean value of the 12 meridians measured in both groups, with means of 14.95 +/- 26.86 microm in the clear corneal group (P =.001) and 16.22 +/- 21.23 microm in the scleral tunnel group (P =.002). There were no statistically significant postoperative differences in the central, midperipheral, or incision-site corneal thickness measurements between the 2 surgical techniques (P =.77).

Time-dependent (fourth-dimensional) pachymetry subtraction maps are useful for following corneal dynamics over time. This study found that small-incision phacoemulsification techniques--scleral and corneal tunnel--had a minor but similar effect on corneal thickness 4 weeks after surgery.