Is there more risk with 25-gauge vitrectomy?

"Endophthalmitis is the most dreaded complication after any intraocular procedure," said Dr. Kunimoto here at the American Academy of Ophthalmology annual meeting. "It has been well documented that different procedures are associated with different rates of endophthalmitis. For example, endophthalmitis occurring after trabeculectomy has an incidence of about 1 in 500 cases, after cataract about 1 in 1,500 cases, and after vitrectomy about 1 in 2,500 cases.

"In contrast, 25-gauge vitrectomy is initiated by placing three cannulas through the conjunctiva, sclera, and pars plana. At the end of the procedure, the cannulas are removed and the wounds are self-sealing because of the small incision size," he explained. Dr. Kunimoto is in private practice in Phoenix.

Dr. Kunimoto and colleagues examined 8,601 consecutive patients who had undergone vitrectomy at Wills Eye Institute, Philadelphia, during a 3-year period. The eight patients in whom endophthalmitis was diagnosed after vitrectomy were included in the study.

"All were analyzed for medical conditions that might predispose them to the development of endophthalmitis, such as surgical indications, operative complications, postoperative hypotony, and antibiotic use," he reported. "No risk factors for the development of endophthalmitis were identified. None of these eight patients received either preoperative antibiotic drops or postoperative oral antibiotics. All of the eight patients received perioperative povidone-iodine and all were left with fluid-filled eyes."

A total of 5,498 patients underwent 20-gauge vitrectomy, and 3,103 underwent 25-gauge vitrectomy. "One of the 5,498 patients that underwent 20-gauge vitrectomy developed endophthalmitis, yielding an incidence of 0.018%, and seven of the 3,103 patients treated with 25-gauge vitrectomy developed endophthalmitis, yielding an incidence of 0.23% [p = 0.004 by Fisher's two-tailed exact test]. This represents a greater than 12-fold difference between the two groups," Dr. Kunimoto said.

The setting for endophthalmitis

Dr. Kunimoto suggested reasons for the difference in the rates of endophthalmitis between the two groups. The first is that sclerotomy wounds that are not sutured at the end of surgery may allow normal eye flora access during the postoperative period. That fact, coupled with the knowledge that the wounds need about 2 weeks to close completely, may provide the setting for endophthalmitis to develop. This scenario also occurs after cataract surgery, he said, with higher rates of endophthalmitis associated with clear corneal wounds.