Randomized clinical trial adds evidence to better integrity of microcoaxial incisions

A randomized, masked, clinical trial evaluated the integrity of phacoemulsification incisions by measuring ingress of ocular surface fluid using trypan blue as a quantifying tracer. The results favored use of either a 2.2-mm microcoaxial or 2.8-mm standard coaxial incision versus smaller bimanual incisions.

Key Points

Chicago-Microcoaxial, bimanual, and standard coaxial phacoemulsification incisions all allow ingress of ocular surface fluid. The amount of fluid ingress is significantly greater in eyes with bimanual incisions compared with those operated on using either the microcoaxial or standard coaxial techniques, however, according to the results of a prospective, masked, randomized clinical study reported by Shetal Raj, MS, at the annual meeting of the American Society of Cataract and Refractive Surgery.

"There have been concerns about the integrity of bimanual phaco incisions and, therefore, the risk of postoperative anterior chamber contamination in eyes operated on with this surgical technique. This clinical study was undertaken to validate findings from a previous study we performed in an animal model where we noted bacterial ingress into the anterior chamber was significantly higher using the bimanual technique compared with microcoaxial surgery," said Raj, Iladevi Cataract and IOL Research Centre, Ahmedabad, Gujarat, India.

"Collectively, these results indicate that it is not the size of the incision that is important for sealing, but rather that architecture and morphology are the critical factors in wound integrity," she added.

All surgeries were performed by a single surgeon, Abhay R. Vasavada, MD, using a standardized technique involving a single-plane, temporal approach. Microcoaxial surgery was performed through a 2.2-mm single-plane incision with a 1.0-mm paracentesis. Coaxial surgery involved a 2.8-mm incision with a 1.0-mm paracentesis; the bimanual technique used a 1.2-mm incision for the phaco tip and a 1.4-mm incision for the irrigating chopper.

Eyes within each of the three surgical groups then were further randomly assigned to one of two subgroups for measurement of trypan blue ingress into the anterior chamber after either cortex removal or IOL implantation.

"These two time points were chosen to isolate the impact of the surgical technique and avoid confounding of the results by mechanical stretching of the incision that can occur with IOL implantation," Raj said.

To quantify the trypan blue ingress after cortex removal, the incisions were hydrated, the speculum was removed, and 0.5 ml of 0.0125% sterile trypan blue was applied over the conjunctiva. Then the patient was asked to blink. After 2 minutes, excess dye was washed off the surface with balanced salt solution, and 0.1 ml of aqueous humor was aspirated from the anterior chamber.

Optical density of the aqueous humor sample was measured using an ultraviolet spectrophotometer. The data were calibrated using a standard graph created from different dilutions of trypan blue measured at 595 nm. For ease of statistical comparison between groups, the data were converted to logs of dilutions.

At both measurement intervals, the results indicated significantly higher ingress of trypan blue originating from the ocular surface in the bimanual group compared with each of the other surgical arms. There were no significant differences comparing the microcoaxial or standard coaxial groups.

"The findings of this study also are consistent with a histological study we performed in rabbits, where we found the bimanual incisions are more prone to damage during surgery. Similarly, other investigators have shown that the bimanual phaco incisions are prone to damage and therefore at increased risk of leakage and penetration of ocular surface fluid," Raj said.