Microincision procedures alter corneal wound architecture

Key Points

"Microincision cataract surgery is increasing in popularity," said Dr. Weikert, assistant professor of ophthalmology, Baylor College of Medicine, Houston. "Bimanual microincision cataract surgery has been gaining acceptance in recent years, and coaxial microincision cataract surgery is a procedure that was introduced recently. Previous studies have found trauma related to the incision with scanning electron microscopy in both conventional small-incision cataract surgery and bimanual microincision cataract surgery."

Dr. Weikert and colleague Douglas Koch, MD, conducted a study to evaluate the changes in the wound architecture regarding the loss of endothelial cells and trauma to Descemet's membrane in both the bimanual and coaxial techniques at the site of the phacoemulsification needle site, the irrigation or second instrument site, and the site through which the IOL was injected.

The bimanual procedure was performed using a certain phaco system (Sovereign with WhiteStar, Advanced Medical Optics), phaco needle (MST, MicroSurgical Technology), and 20-gauge irrigating chopper (DuoMax, ASI CO). Paracenteses were made using a 1.3-mm blade (V-Lance, Alcon Laboratories). The IOL was inserted through a separate incision using either a 3.0- or 2.3-mm blade, he said.

The coaxial procedure was done using tri-modal cataract removal instrument (Infiniti, Alcon Laboratories) with a flared 30° round tip with a micro-smooth ultrasleeve. The procedure was done through an incision created using a 2.3-mm steel knife, and the second instrument was a Nagahara chopper used through a 1.3-mm paracentesis. In this procedure, the IOL was injected using a specific delivery system (Monarch II, Alcon Laboratories) through the phaco wound, according to Dr. Weikert.

The investigators evaluated the intraoperative phaco time and other phaco parameters and measured the incisions before and after the surgery. Then the corneas were harvested, and scanning electron microscopy was performed to determine the features of the wound.

For both procedures, there was a slight increase in the size of the wound preoperatively to postoperatively, Dr. Weikert said.

In light of data from previous studies showing no substantial changes to the external corneal surface, the investigators focused on the alterations in the internal cornea. To optimize their results, each scanning electron micrograph was used at a consistent level of magnification. Image processing software was used to measure the area of endothelial cell loss surrounding each surgical incision. Three area measurements were taken for each incision, which agreed within 0.05 mm² , Dr. Weikert said.

Endothelial cell loss

"In assessing the damage to the corneal endothelium, the mean cell loss surrounding the phaco wounds was slightly greater in the eyes treated with the microcoaxial procedure as compared with the phaco site in the bimanual cases," he reported.

Regarding the wound made by the second instrument, the area of endothelial cell loss was slightly greater with the bimanual procedure compared with the coaxial procedure, but the two procedures did not differ substantially.

"Considering the total endothelial cell loss and the differences at each wound, the total areas between the procedures were fairly equivalent," he stated.

When the investigators considered the trauma to Descemet's membrane, Dr. Weikert found that "tears occurred in three varieties. There was either extension at the wound edge, incision rupture of the posterior lip of the wound, or flap loss of Descemet's membrane."