July 2007




Preserving corneal architecture

by Rich Daly EyeWorld Contributing Editor




Research provides controversial support for a procedure that combines old and new surgical approaches

Uneventful bimanual microincision cataract surgery that provided good results with damage to the corneal architecture.

Source: Rosa Braga-Mele M.Ed, MD. FRC

Microincision coaxial phacoemulsification matches standard coaxial phacoemulsification in lower rates of induced wound changes that lead to wound leakage when compared with microincision bimanual phacoemulsification, according to recent research.

The findings were based on a prospective study of 15 human cadaver eyes (three groups of five eyes) ranging from one to four days postmortem that underwent simulated phacoemulsification by bimanual phacoemulsification (1.2-mm incision), standard coaxial phacoemulsification (2.75 mm), or microincision coaxial phacoemulsification (2.2 mm). All phaco settings were kept constant in each group, and after phaco, IOP was cyclically raised and lowered from 0 to 125 mm Hg.

Spontaneous wound leakage was evident in all five eyes having bimanual phacoemulsification, The study, published in the March issue of the Journal of Cataract & Refractive Surgery, found spontaneous wound leakage in all eyes undergoing bimanual phaco, in one of five eyes having standard coaxial phaco, and in none of the eyes receiving microincision coaxial phaco. India ink penetration was grossly evident in both eyes having bimanual phacoemulsification, one of two eyes having standard coaxial phacoemulsification, and neither of the eyes having microincision coaxial phacoemulsification.

Scanning electron microscopy showed increased endothelial cell loss and greater compromise to Descemet’s membrane with bimanual phacoemulsification than with standard coaxial phacoemulsification or microincision coaxial phaco.

The study is the comparison of wound morphology and integrity among the newer phaco techniques that use smaller incisions: bimanual phacoemulsification and microincision coaxial phacoemulsification. The advantage of the smaller, readily self-sealing wounds created in these surgeries is limited by the maintenance of wound morphology and integrity. This first head-to-head study of bimanual phacoemulsification versus microincision coaxial phacoemulsification aimed to answer the wound integrity questions.

Richard J. Mackool, M.D., clinical assistant professor of ophthalmology, New York Medical College, Astoria, N. Y., said the findings appear to match his clinical experience with the different types of incisions. The advantages Dr. Mackool has seen from microincision coaxial phaco has already led him to use that approach in the “vast majority” of his cataract patients.

“The inescapable conclusion is that incisions through which rigid instruments are inserted are much more likely to be undesirably torn, distorted, and otherwise damaged,” he said.

Doubts raised

The study findings appear to run counter to those from several animal, human, and clinical studies that have shown bimanual phaco to be relatively safe. The difference, according to the study authors, was that those studies primarily addressed corneal wound burn and did not directly study wound integrity.

The results of the study generally run counter to the experience of Mark Packer, M.D., clinical associate professor, Casey Eye Institute, Oregon Health & Science University, Portland, with microincision bimanual phaco, although he has limited experience with microincision coaxial surgery.

“My outcomes with biaxial phaco for routine cases are essentially identical to my outcomes with standard coaxial phaco,” Dr. Packer said.

Dr. Packer prefers the bimanual technique primarily because of the enhanced surgical flexibility and control made possible by separation of inflow and outflow. Among the many advantages he has found from the bimanual approach is the ability to use the irrigation flow from the second handpiece as an adjunctive surgical device to flush nuclear pieces from the angle or to loosen epinuclear or cortical material from the capsular bag.

The leakage findings of the authors appear to be a normal surgical outcome.

“Every surgeon from time to time experiences a non-sealing incision, and in these cases suture closure is usually indicated,” Dr. Packer said.

Dr. Packer uses the Seidel test at the conclusion of every intraocular surgical case to ensure complete incision closure. If the test result is initially positive, he follows up with stromal hydration and massage to facilitate sealing. If leakage continues, he adds a 10-0 nylon suture to close the incision. Dr. Packer also was critical of the study’s use of cadaver eyes because they lack the activity of the endothelial pump. The negative intrastromal pressure is a critical force in self sealing clear corneal incisions, he said.

The surgical approach of the study authors also drew considerable criticism from Dr. Packer and Jorge L. Aliу, M.D., Ph.D., Medical Director, Instituto Oftalmologica, de Alicante, and professor and chairman of ophthalmology, Miguel Hernandez University, and Medical Director, Instituto Oftalmologica de Alicante, Alicante, Spain.

Dr. Aliу said the use of “extremely high power” (60% versus his 10 to 20%), continuous mode instead of a hyperpulse mode, and higher vacuum levels could result in a very different impact of the phaco tip on the wound incision.

Despite those reservations, Dr. Aliу said some of the results are not in contradiction with his own clinical experience. His previously published research detailed the decreased vectorial astigmatic changes in the corneas that microincision coaxial cataract surgery provides, as well as decreased effective phaco time. The main value of the study is to contribute to a “better understanding of how we should manipulate or build up the instruments when incision size decrease is the target,” he said.

Dr. Aliу found similarly leaking incisions during his learning period with microincision coaxial surgery. As experience grows, incisions as small as 0.7 mm regularly produce stable wounds.

“So, in part [the study authors] are right and it might be that the results can be applicable to novel MICS [microincision cataract surgery] surgeons,” Dr. Aliу said.

Editors’ note: Dr. Packer has financial interests with Advanced Medical Optics (AMO, Santa Ana, Calif.), eyeonics (Aliso Viejo, Calif.), and Alcon (Fort Worth, Texas). Dr. Mackool has financial interests with Alcon. Dr. Aliу does not have any financial interests related to his comments.

Contact Information

Mackool: 718-228-3400, mackooleye@aol.com

Packer: 541-687-2110, mpacker@finemd.com

Aliу: +34-965 150-4 025, jlalio@vissum.com

Preserving corneal architecture Preserving corneal architecture
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