The goal of ophthalmic surgery is to achieve the desired effect with minimal trauma to the eye, as such, creating smaller incisions for clear cornea phacoemulsification continues to garner significant interest because it has been shown to decrease induced astigmatism and the need for suturing.¹ Currently, there are two methods of performing microincisional cataract surgery: bimanual and microincisional coaxial (microcoaxial) phacoemulsification.

Both bimanual and microcoaxial techniques use smaller incision sizes. Here, we will refer to our knowledge of the bimanual and microcoaxial techniques that induce two 1.2 mm and one 2.2 mm incision, respectively. Several firms have, however, recently manufactured surgical instruments that create even smaller incisions with both techniques, though the availability of and experience with these new devices is currently very limited.

Many researchers have reported the advantages of bimanual phaco to include less surgically-induced astigmatism, increased followability of nuclear fragments and the added flexibility of using two incisions, allowing differing angles for the surgical approach,^2,3 whilst disadvantages include anterior chamber instability, potential wound trauma and lower vacuum levels. With regards to microcoaxial phaco, less endothelial cell loss and less Descemet's membrane trauma have been reported,^4,5 however, the disadvantages of the technique have been found to be similar to those encountered in standard coaxial phaco, such as, difficulty in removing the sub-incisional cortex and decreased followability, as irrigation may push nuclear fragments away from the phaco tip.

Because of the paucity of studies regarding microcoaxial phaco, we sought to directly compare the wound integrity of incisions made using bimanual phacoemulsification with standard coaxial phaco and microcoaxial phaco, by observing wound leakage, histopathological evaluation of the wound and scanning electron microscopy (SEM) of the endothelial surface of the wound.

Bimanual pitched against coaxial & microcoaxial phaco

Table 1: Ultrasound parameters and instrumentation in phacoemulsification techniques.

Our study included fifteen human cadaveric eyes (five in each group) randomized for either standard coaxial, microincisional coaxial, or bimanual simulated cataract extraction. Each eye was exposed to continuous phacoemulsification with the tip positioned over the pupil centre for a total of two minutes, with five to 10 second alternating intervals of simulated occlusion (by pinching off the aspiration line) followed by non-occlusion. The Infiniti system (Alcon, USA) was used for coaxial eyes and the Sovereign system (Advanced Medical Optics, USA) was used for the bimanual eyes and comparable phaco settings were chosen for both. The Infiniti system was set with 60% fixed power in continuous pulse mode (17 pps) with a 35% on and 65% off-duty cycle, 12 cc/min aspiration and 300 mmHg vacuum. The Sovereign system was set in Whitestar mode with 60% power and C/F mode with a 33% on and 67% off-duty cycle, 12 cc/min aspiration and 300 mmHg vacuum. Incision size, handpiece tips and ultrasound times are summarized in Table 1.

After completing the simulated phaco cycle, the intraocular pressure (IOP) was cyclically raised and lowered from 0 to 125 mmHg in all eyes for 30 seconds while the wounds were monitored for spontaneous leakage. We processed two corneas from each treatment group for histologic evaluation to determine India ink penetration into the corneal wounds, and performed SEM on one cornea from each treatment group to evaluate Descemet's membrane and the corneal endothelium.