Corneal incision size makes little diffrence in cataract extraction

June 1, 2011

Clear corneal microincisions of 2.2 and 1.8 mm produce similar low levels of surgically induced astigmatism after cataract extraction.

The 1.8-mm incision causes less modification in the K values and less surgically induced magnitude and scatter, but the difference between these parameters and those measured with the 2.2-mm incision was not significant. Dr. Febbraro presented his findings at the annual meeting of the American Society of Cataract and Refractive Surgery.

The evolution of the technologies used in cataract extraction surgery has included creation of progressively smaller incisions in the hope of inducing less astigmatism postoperatively and lowering the incidence of serious infections. The standard 3-mm incision decreased in size over time to 2.2 mm and even further to 1.8 mm along with the evolution from standard phacoemulsification cataract extraction (PKE) to microcoaxial PKE.

Astigmatism study

A total of 116 eyes were included in this nonrandomized prospective series. Group 1 was composed of 54 eyes that underwent PKE in which a 2.2-mm superior clear corneal incision was created and a microincision cataract surgery (MICS) IOL (Akreos Microincision, Bausch + Lomb) was implanted, and group 2 was composed of 62 eyes that underwent PKE in which a 1.8-mm superior clear corneal incision was created and an Akreos MICS IOL was implanted using a wound-assisted technique. In both groups, the incision was a two-plane wound that was not enlarged to facilitate implantation of the IOLs, Dr. Febbraro said.

Astigmatism was measured using an autorefractometer (ARK-560, Nidek) preoperatively and 1 month postoperatively. Surgically induced astigmatism was measured using the arithmetic method by subtracting the preoperative K values from the postoperative values and by the Alpins method of vector analysis in which the magnitude and axis changes in the keratometry astigmatism were calculated. Surgically induced astigmatism Polar Plots (Eye Pro 2011) were created.

Using the arithmetic method, in group 1 with the 2.2-mm incision, the mean preoperative astigmatism was 0.58 ± 0.46 D and the mean postoperative astigmatism was 0.76 ± 0.43 D, a difference that reached significance (p = 0.0018). In group 2, with the 1.8-mm incision, the mean preoperative astigmatism of 0.66 ± 0.45 D increased negligibly to 0.67 ± 0.49 D, which did not reach significance (p > 0.05).

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