Endophthalmitis higher with CCI than scleral tunnel

San Francisco-A number of studies have suggested an increased rate of endophthalmitis with clear cornea surgery compared with scleral tunnel surgery, and potential causes of this increase include incision location, incision architecture and changes in antibiotic prophylaxis, according to David G. Hwang, MD.

Possible reasons include the absence of the conjunctiva as a barrier, location of temporal incisions in the exposed interpalpebral fissure rather than under the upper lid, and the use of an incision architecture that does not prevent bacterial entry into the eye, Dr. Hwang said. He is professor of ophthalmology, and director, Cornea Service, University of California, San Francisco.

Several studies Speaking in a session on primary eye care management problems, Dr. Hwang presented findings from several studies that support his contention that the rate of endophthalmitis is higher with clear cornea incisions.

In a study of cadaver eyes subjected to experimental clear cornea incisions done in a one-plane fashion, investigators showed that at lower IOPs there was gaping of the posterior wound, demonstrated by optical coherence tomography. India ink placed on the surface showed entry of these particles into the superficial and the deeper layers of the incision, and presumably it was also possible for the particles to enter the eye itself, Dr. Hwang explained.

In addition, one eye bank study showed that there are differences in resistance to an external pressure placed on eyes that have been subjected to differing incision architectures.

For example, with a one-plane clear corneal incision with a pressure of 22 mm Hg, the bursting strength was reduced by half when the pressure was reduced to 12 mm Hg. This suggests that pressurizing the anterior chamber may have only transient benefits in terms of creating a seal, Dr. Hwang said.

"Creating a two-plane incision had no additional benefit, but a three-plane incision was somewhat better than the one-plane incision," he added. "In fact, we could also reproduce that same benefit by moving the one-plane incision closer to the limbus. But by far the most important benefit was by lengthening the tunnel so that we created a square incision. This had the strongest architecture of them all.

"Based on these studies and others, we would suggest that a self-sealing wound architecture would ideally be based at the limbus, would have multiple planes, and most importantly would have as long a tunnel as possible, ideally with the length equaling the width of the incision," he continued. "This should be largely self-sealing at normal IOPs with minimal hydration, and we should therefore suture any incision that leaks or an eye that is at high risk for endophthalmitis, such as a case of a torn posterior capsule."

Prophylaxis Antibiotics and antisepsis prophylaxis is another critical issue in prevention of endophthalmitis. With the transition to clear cornea incisions, surgeons have continued to use povidone-iodine antisepsis while simultaneously moving away from subconjunctival antibiotic injections and in many cases toward antibiotics in irrigating solutions or the exclusive use of topical antibiotics, predominantly fluoroquinolones.

While there are data suggesting a trend toward a protective effect from antibiotics, human studies have found no decrease in the culture positivity rate of anterior chamber aspirates from povidone-iodine-treated patients who have additionally had preoperative topical antibiotics compared with those who have not, Dr. Hwang said.

Evidence of a protective effect is stronger, however, with subconjunctival antibiotics, he added.

"The question really becomes: 'Can we provide an equivalent degree of antibiotic delivery with newer drugs or improved dosing regimens as these traditional subconjunctival antibiotics provided?' " he said.