Cataract surgeons agree that proper incision construction is paramount for achieving good postoperative stability that will reduce the risk for endophthalmitis. The safety of the clear cornea incision technique versus use of other incision types remains controversial, however.
New Orleans-The role of less-forgiving incisions as a risk factor for post-cataract surgery endophthalmitis has been a subject of discussion for years. During the Spotlight on Cataracts session at the annual meeting of the American Academy of Ophthalmology, I. Howard Fine, MD, spoke in support of the clear cornea incision (CCI) technique he introduced in 1992 and focused on the need for attention to detail in its construction and management. In a follow-up presentation, Paul H. Ernest, MD, also concentrated on the importance of adhering to principles of good wound construction and encouraged attendees to incorporate elements that increase the margin of safety.
Noting that the overwhelming majority of cataract surgeons now have adopted CCIs, Dr. Fine said that the available literature examining the association between CCIs and postoperative endophthalmitis is contradictory. Although some studies demonstrate that a recent increase in prevalence of endophthalmitis corresponds with use of a CCI, other large studies found no association.
The latter research includes a study of more than 100,000 patients operated on in the United Kingdom between 1996 and 2004; a 20-year study of cataract surgeries performed in western Australia; an investigation of 20,000 U.S. patients whose surgeries included a CCI and a topical, fourth-generation fluoroquinolone for endophthalmitis prophylaxis; and a Swedish study specifically designed to examine the incidence of endophthalmitis in relation to incision type.
"In our practice, Dr. Mark Packer, Dr. Richard Hoffman, and I have operated through a temporal CCI in more than 10,000 eyes and over 11 years without a single case of endophthalmitis," said Dr. Fine, clinical professor of ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland.
Dr. Fine told attendees that other factors must be considered for their possible role in an increasing rate of endophthalmitis, among them the change in antibiotic resistance among the gram-positive microorganisms that are the leading pathogenic cause of post-cataract surgery endophthalmitis. Incision construction also is paramount, Dr. Fine said, adding that its role is recognized in the conclusion of an American Society of Cataract and Refractive Surgery (ASCRS) white paper on the association between CCIs and the risk of postoperative endophthalmitis (J Cataract Refract Surg. 2006;32:1556-1559).
"In its report, the authors from the ASCRS Cataract Clinical Committee stated that with the appropriate use of aseptic methods, including careful draping, chemoprophylaxis-and, particularly, CCI design, construction, and sealing-the risk for infection can be appropriately low," said Dr. Fine, who also is in private practice in Eugene, OR.
"Cataract surgery begins with incision construction," he continued. "Clearly, however, not all CCIs are the same, and we cannot lump them all together and discuss them as if they were. The literature on this topic is incomplete because there has been no standardization or description of CCI construction, architecture, or profile in the published studies."
Dr. Fine told attendees that with the exception of transitioning to use of trapezoidal blades, his method for making a CCI has remained constant since he first introduced the technique 15 years ago: he makes the incision in the plane of the cornea with a chord length equal to at least 2 mm.
Recently, Dr. Fine said, a study using anterior segment optical coherence tomography (OCT) for in vivo imaging to examine the profile of CCIs revealed some interesting findings.
"We documented by OCT that our technique creates an incision with an arcuate configuration that is longer than the chord length we were measuring and that features a uniquely advantageous architecture characterized by a tongue-and-groove-like fit between the incision floor and roof," he said. "Our OCT studies also showed that our practice of routinely performing stromal hydration at the end of the case results in stromal swelling that persists for at least 24 hours. That factor combined with the stability conferred by the unique architecture of our CCIs results in adequate self-sealability that is the critical factor in our long history of clear cornea surgery with no cases of endophthalmitis."
In addition to performing stromal hydration of the CCI and the side port incision, Dr. Fine and colleagues always verify incision sealability using fluorescein dye, he said. Although formerly they digitally applied pressure to the incision to check for leakage, Dr. Fine added, they have abandoned that step because such pinpoint pressure is likely to induce leakage but unlikely to occur in the postoperative period.
He also told attendees that his research indicates that surgeons need to pay more careful attention to constructing the side port incision. A simultaneous shift to temporal surgery and CCI use may play a role in the increase in endophthalmitis rates, too, Dr. Fine said.
"For a right-handed coaxial surgeon operating on left eyes, the side port incision is located in the inferior conjunctiva cul-de-sac. It would be interesting to review the literature reporting an increased incidence of endophthalmitis with CCI to see if it was left eyes that predominated. Perhaps this factor is the culprit in what appears to be an increased incidence of endophthalmitis with the introduction of the CCI," Dr. Fine said.
Dr. Ernest reviewed the principles of good wound construction and discussed how these principles are implemented with various incision types.
Recognizing that a well-constructed wound should have the proper dimensions to prevent egress of fluid and ingress of bacteria, allow for the tissue to return to its original configuration after being stretched intraoperatively, and seal as rapidly as possible, he said that evidence provided by carefully designed scientific studies favors limbal incisions over CCIs.
"Geometry, tissue properties, and histology are the critical components of the ideal cataract incision. With the goal of minimizing endophthalmitis risk, I would encourage surgeons to incorporate as many factors into their procedure as they feel comfortable, to optimize those features," said Dr. Ernest, in private practice in Jackson, MI, and founder of TLC Eye Care of Michigan.
Reviewing the related evidence, Dr. Ernest cited studies that he and other researchers have conducted using basic engineering and scientific principles and incorporating rigorous methodology to examine the features contributing to ideal wound performance. The studies included extreme challenges to elicit changes in the performance of differently constructed wounds, tested a single variable at a time to eliminate potential confounding, and included repeat testing for verification of the accuracy of the findings.
Regarding geometry, Dr. Ernest said that the available research indicates that square wounds are desirable because they provide the greatest mechanical stability as well as the greatest refractive stability. Rectangular wounds are less stable and also are susceptible to changes in IOP, he said. Comparing limbal and corneal incisions, Dr. Ernest noted that limbal incisions always are square, and with the advent of microincision techniques, cornea incisions also can be created with a square architecture.
With respect to tissue properties, elasticity is desirable because it allows the tissue to return to its original configuration after being distorted by surgical instrumentation, he said. Limbal incisions fulfill that criterion because elastin is found in the limbus but is not present in corneal tissue, Dr. Ernest added.
With the use of sutureless techniques, rapid sealing is desired, he said. All incisions heal via the action of fibroblasts, but histologic studies show a dramatic difference in the time to healing comparing incisions created in the vascular-based limbus versus in clear cornea, Dr. Ernest said. Limbal incisions heal in 7 days as a result of fibroblast invasion into the incision site, whereas healing of avascular CCIs depends on keratocytes undergoing metaplasia to fibroblasts and takes 30 to 60 days, he added.
"In the interim period, the incision site is susceptible to ingress of bacteria," Dr. Ernest said.
Although some may argue that the action of the corneal endothelial pump contributes to immediate sealing of clear corneal wounds, Dr. Ernest said that his research suggests that the endothelial pump is not a key factor affecting wound stability. Studies evaluating resistance to external pressure of 3-mm incisions created in cadaver and cat eyes demonstrated that at 4 days after surgery, no difference existed between the two models in the amount of applied pressure that induced leakage of CCIs. A comparison of limbal incisions, however, showed that the resistance to pressure was twofold higher in the cat eye compared with the cadaver eye.
"These findings indicate the viable endothelial pump in the cat eye provided no benefit for improved stability of the CCI and demonstrate the importance of fibroblastic activity for incision sealing," Dr. Ernest said.
Ballooning of the conjunctiva may occur with limbal incisions only, and it represents an adverse feature of that technique, he said. Conjunctival ballooning results if the keratome blade nicks the posterior conjunctiva as the surgeon drags the tissue into the incision, Dr. Ernest said, adding that careful surgical technique can prevent this complication.
"The likelihood of conjunctival ballooning also is decreased now with the advances in phaco technology that allow tighter-fitting wounds so there is less egress of fluid even if the conjunctiva is nicked," he said. "If a buttonhole is inadvertently made in the conjunctiva, however, surgeons also can perform a mini-peritomy to solve the problem."OT