Square incision for implanting toric intraocular lens provides refractive results

May 15, 2010

The use of a toric IOL corrects low levels of preoperative astigmatism in patients undergoing cataract surgery.

In addition, using square wounds and starting farther back provides a better refractive result, said Dr. Ernest, a private practitioner in Jackson, MI, and on the clinical staff of Kresge Eye Institute, Detroit.

He described two studies: the first reported the combined results of two surgeons using two different incisions, and a second retrospective study of patients who underwent surgery performed by Dr. Ernest, using the square limbal incision only.

Dr. Ernest and co-author Edward J. Holland, MD, a practicing ophthalmologist with Cincinnati Eye Institute, Cincinnati, conducted a prospective study that included 25 patients (30 eyes) with about 1 D of pre-existing corneal astigmatism. The purpose of the study was to determine patient response to the toric IOL.

The investigators found, on average, that there was a decrease in the postoperative cylinder to 0.4 D from preoperative levels ranging from 0.75 to 1.03 D. In addition, they also found that patient satisfaction was good. On a scale of 1 to 5, the distance vision was scored from 4.4 to 4.6. About 74% of the patients did not wear spectacles for distance vision postoperatively compared with 65% of patients who depended on spectacles for distance vision preoperatively, Dr. Ernest said.

He pointed out two problems with the study over and above the small sample size. The first was a difference in the surgically induced astigmatism between the two surgeons that was the product of two different incision types used during the surgeries. Dr. Holland used a clear corneal incision and Dr. Ernest used a square limbal incision. A comparison of the two incision types showed that the clear corneal incision induced a mean of 0.6 ± 0.4 D and the square limbal incision induced 0.3 ± 0.2 D, with the square limbal incision inducing about half the astigmatism of the clear corneal incision.

"My belief in using square wounds and starting farther back is demonstrated by the results," Dr. Ernest said.

Another problem with the study was the blending of two different surgeons, two different surgically induced levels of astigmatism, and no controls.

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