Square and nearly square incisions prevent hypotony

July 1, 2007

Clear corneal wounds-with square or nearly square surface architecture-that are meticulously checked for incisional sealing are stable postoperatively, as demonstrated by the absence of hypotony and wound leakage. In a sealed clear corneal wound, IOP remains reasonably stable relative to the level set at the conclusion of the procedure.

Key Points

"An association has been described between clear corneal incisions and postoperative infection after cataract surgery," said Dr. Belani, who is involved in clinical research and part-time practice at Advanced Vision Care, Los Angeles, and in part-time practice at Kaiser Permanente West Los Angeles.

"Although not universal, the literature suggests this trend. Peter McDonnell, MD, and colleagues from the Wilmer Eye Institute, Baltimore, have indicted that incisions are unstable at low IOPs, although wound construction and architecture were not emphasized," she said.

"Corneal tunnels, for example, are not as easy to control as scleral corneal tunnels, because the latter are made in multiple planes with a dull blade. Clear corneal tunnels are typically created with a very sharp blade and a single-pass incision," she said.

Beside shape and blade sharpness, other factors that affect the wound construction are IOP, tissue thickness and rigidity, and the surgeon, Dr. Belani noted.

She recounted that postoperative hypotony after clear corneal cataract extraction was reported in 2001 (Shingleton BJ, Wadhwani RA, O'Donoghue MW, Baylus S, Hoey H. Evaluation of intraocular pressure in the immediate period after phacoemulsification. J Cataract Refract Surg. 2001;27:524-527) and more recently by her group (Masket S, Belani S. Proper wound construction to prevent short-term ocular hypotony after clear corneal incision cataract surgery. J Cataract Refract Surg. 2007;33:383-386). Dr. Shingleton and colleagues created unsutured 3.0-mm incisions and found that 20.5% of eyes had IOP of ≤5 mm Hg by 30 minutes postoperatively.

In addition, Dr. McDonnell found that these wounds in rabbits and humans are unstable at IOP levels of < 10 mm Hg and reported wound gaping at these IOP levels that resulted in fluid leakage out of the anterior chamber, hypotony, and a negative pressure gradient that allows fluid flow back into the anterior chamber.

To address the question of whether proper wound construction-i.e., square incisions combined with meticulous control of incisional seals-can prevent hypotony early postoperatively after clear corneal incision cataract surgery, she and co-author Samuel Masket, MD, evaluated 2.2-mm and 3-mm clear corneal cataract incisions with square or nearly square surface architecture for stability. They retrospectively reviewed the charts of 60 patients who had undergone clear corneal cataract extraction by microcoaxial phacoemulsification from January to September 2006. A square 2.2-mm incision had been used in 50 patients, and a nearly square 3-mm incision had been used in 10 patients.

"Initially, the IOP was elevated to seal the internal lips of the wound and then lowered to physiologic levels of about 15 to 20 mm Hg and measured with a tonometer. The hermetic sealing of the wound was confirmed by Seidel testing," Dr. Belani said.

Two to 6 hours after the conclusion of the surgery, IOP levels were measured.

The mean IOP level postoperatively in the 50 eyes with 2.2-mm square incisions was 19.2 mm Hg, and in the 10 eyes with a 3-mm nearly square incision, it was 16.6 mm Hg. No patient had an IOP less than 10 mm Hg. No suture was required in any eye. No hypotony or wound leakage was seen in any patient at any point after surgery. Although this was a very small study to determine efficacy, no infections were noted in any eyes, Dr. Belani reported.

"We believe that the IOP level early after surgery is a valid marker of wound stability. An incompetent, poorly constructed clear corneal incision may be associated with hypotony, leakage, and an increased infection rate. Careful wound construction with appropriate architecture, that is, square wound construction, combined with hermetic sealing, should reduce this tendency," she concluded.