February 2007

 

CATARACT/ IOL

 

Wound construction key to avoiding endophthalmitis


by Tony Realini, M.D.

 

 

 

High-risk aspects of clear corneal incisions identified in study

In Hovanesian's study, eight eye bank corneas (courtesy of Vision Share) were mounted on an artificial anterior chamber. India ink was used for to test for ingress and egress of fluid through cataract wounds at different simulated intraocular pressures.

Source: John Hovanesian, M.D.

Post-op endophthalmitis is the most dreaded complication following cataract surgery. Most often it occurs unexpectedly in eyes that underwent uncomplicated surgery. As cataract surgical techniques evolve, wound construction has become an important factor in determining the risk of endophthalmitis.

"Recent reports have shown a substantial increase in the incidence of post-operative endophthalmitis after cataract extraction in the last decade," said Massimo Busin, M.D., Forli, Italy. He pointed out that this coincides with the change from scleral tunnel incisions to sutureless clear corneal incisions.

John Hovanesian, M.D., Laguna Beach, Calif., agreed. “Initially, a beveled corneal incision will self-seal, because hydrostatic pressure in the eye forces the internal lip of the wound closed. Intraocular pressure drops in the first few hours after surgery, and wound gape allows surface contaminants to enter the anterior chamber.”

Identifying risk for endophthalmitis

To identify which aspects of clear corneal wounds increase the risk for endophthalmitis, Dr. Busin and several colleagues undertook a retrospective analysis of nearly 10,000 eyes undergoing cataract surgery via clear corneal incisions between 1996 and 2005. The research team evaluated three parameters of the corneal wound: its location (nasal or temporal), with (5.5 versus 3.2 mm), and whether or not a suture was placed.

"All patients underwent a standard procedure by one of two surgeons," said Dr. Busin. In all cases, the surgeon sat at the 12 o'clock position. "Therefore, all right eyes were operated on through a temporal approach and all left eyes through a nasal approach."

Eyes were fairly evenly divided between the nasal and temporal approaches. Approximately two-thirds of patients had suture closure of the incision. "In about one-fourth of patients, the incision was enlarged from 3.2 mm to 5.5 mm for implantation of a rigid PMMA lens,” said Dr. Busin.

Post-op endophthalmitis developed in 17 of the 9,663 eyes (0.18%). Of these, 15 occurred in eyes with temporal incisions (15 of 4,893; 0.31%) and two in eyes with nasal incisions (2 of 4,770; 0.042%).

Sixteen cases of endophthalmitis occurred in eyes that did not receive a suture (16 of 3,984; 0.4%), and only one case of endophthalmitis occurred in an eye that did receive a suture (1 of 5,679; 0.018%).

Endophthalmitis occurred in six eyes with 3.2-mm incisions (6 of 7,297; 0.08%) versus 11 eyes with 5.5 mm incisions (11 of 2,366; 0.46%).

Concluded Dr. Busin, "A larger, temporal, unsutured, clear corneal tunnel exposes cataract patients to an increased risk of developing post-operative endophthalmitis."

Source: John Hovanesian, M.D.

Clear cornea incisions are frequently left unsutured after surgery, with the assumption being that they are self sealing. Ashley Behrens, M.D., Wilmer Eye Institute, Johns Hopkins University, Baltimore, recently conducted an evaluation of clear cornea cataract incisions using a new anterior segment optical coherence tomography (OCT) instrument.

Dr. Behrens and his group obtained OCT images on eight patients 24 hours after uncomplicated clear cornea cataract surgery. "At the slitlamp, the clear corneal wounds appeared well-apposed and no apparent leakage was observed in any of the examined patients. However, the OCT images revealed a partial wound gape in two of the eight patients,” said Dr. Behrens. “Interestingly, these two patients had the lowest IOP values of the group, approximately 10 mm Hg each." "These findings serve as additional evidence that self-sealing clear corneal wounds may gape spontaneously during the early post-operative period," he said.1 Prevention is the best treatment for endophthalmitis. To this end, Dr. Hovanesian and colleagues have developed a technique to create a watertight seal in clear corneal incisions in the immediate post-operative period by using fibrin adhesive. The adhesive comes in two parts, the fibrinogen portion and the thrombin portion; when these two portions come into contact, the adhesive is formed.

Their delivery of these two components of the fibrin adhesive into the wound is simple. At the completion of the operation, the top of the keratome is coated with the fibrinogen portion, and the bottom is coated with the thrombin portion.

“The knife is then carefully inserted without cutting tissue back into the incision, to coat the anterior and posterior aspects of the incision with fibrinogen and thrombin, respectively.” said Dr. Hovanesian. "When the knife is withdrawn, the two compounds mix, sealing the wound."1 The adhesive polymerizes within 30 seconds, he said.

He tested this method using eight eyebank eyes. After constructing 2.5–mm clear corneal incisions with the keratome, four were sealed using fibrin adhesive and four were left unsealed. An artificial anterior chamber was used to deliver balanced salt solution (BSS), and IOP was adjusted by raising and lowering the BSS bottle. India ink was used to test for wound leaks at both low and high IOP.

“All four control eyes without adheasive had ingress of India ink at low and high IOP,” said Dr. Hovanesian. “In contrast, none of the four eyes sealed with fibrin adhesive had ingress of fluid at low or high IOP.”

While this study provides preliminary evidence that clear corneal incisions can be sealed using fibrin tissue adhesive, "The potential toxicities of fibrin adhesive to intraocular structures have not been carefully studied and require further investigation," said Dr. Hovanesian.

Editors’ note: Dr. Realini is associate professor of ophthalmology, West Virginia University Eye Institute, Morgantown, and participates in the speakers' bureau for Alcon (Fort Worth, Texas), Allergan (Irvine, Calif.), Merck (Whitehouse Station, N.J.), Novartis (Basel, Switzerland), and Pfizer (New York). He is a member of EyeWorld's editorial board. Dr. Hovanesian is a consultant for Baxter BioScience (Costa Mesa, Calif.); IOP, Inc. (Round Lake, Ill.); DuPont; and Ista Pharmaceuticals (Irvine, Calif.). Drs. Behrens and Brusin have no financial interests related to their comments.

Contact Information

Busin: mbusin@yahoo.com

Hovanesian: DrHovanesian@harvardeye.com

Behrens: abehrens@jhmi.edu

Refrences

1. Behrens A, Stark WJ, Pratzer K, McDonnell PJ. Dynamics of small-incision clear cornea wounds after phacoemulsification surgery in the early postoperative period using optical coherence tomography. J Refract Surg (in press).

Wound construction key to avoiding endophthalmitis Wound construction key to avoiding endophthalmitis
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