VITREOUS LOSS

Femtosecond laser-assisted cataract surgery almost completely, but not quite, eliminates posterior capsule ruptures or vitreous loss, harvey s Uy MD, Manila, Philippines, reported at the annual meeting of the American Academy of Ophthalmology. in his first 500 cases the rate of posterior capsular rupture and vitreous loss was less than one per cent. The majority of these cases had dense (> LOCs iii Grade 4) nuclei. however, the greater tear resistance of laser-assisted anterior capsulotomies appears to better preserve the integrity of the capsular bag, which facilitates management of vitreous loss, he noted.

Dr Uy said that femtosecond laser assistance helps prevent capsular rupture in several ways. The precision of the corneal incision helps stabilise the anterior chamber during surgery, and when fragmenting the lens the device can be programmed to leave an epinuclear plate at the back of the lens that helps prevent inadvertent contact of the posterior capsule by the phacoemulsification tip (Figure 1). Currently, he leaves a 1.0mm gap between the deepest laser cut and the back of the capsular bag. To further reduce the need for phaco power, Dr Uy often uses a pie-cut cutting pattern that allows insertion of a pre-chopper or other similar instrument to divide the nucleus into several pieces before it is evacuated (Figure 2).

[caption id='attachment_2221' align='alignright' width='300' caption='Figure 1. Planning screen capture demonstrating space between the posterior capsule and laser fragmented area that serves as a protective epinuclear plate for the posterior capsule'][/caption]

In the event of a posterior breach, the robust nature of the laser capsulotomy, whose regular edges have been shown to resist radial tears better than those seen in manual capsulorhexes, makes the capsular bag better able to withstand the stress of additional procedures to manage vitreous loss, Dr Uy said. These include anterior vitrectomy and use of tensioning devices to rescue the capsular bag. in the case of weak zonules, the capsule can be suspended with capsular hooks and can be expanded with tensioning rings. Dr Uy presented a case in which a patient suffered a large posterior tear during lens extraction. Because the capsular bag retained some structural integrity, he was able to support the bag and implant the lens in the bag despite the posterior tear. The surgery went well and post-op the patient did well with uncorrected visual acuity of 20/25, he said.

[caption id='attachment_2222' align='alignleft' width='300' caption='Figure 2. Real time image of a laser lens fragmented cataract using pie-cut pattern'][/caption]

In response to questions, Dr Uy added that there are a few complications that are unique to femtosecond cataract surgery. One is that bubbles created by the laser during capsule disruption may lead to a transient increase in intraocular pressure. Another is that proteins released by lasering the lens can block the trabecular meshwork if the interval between softening the lens and removing it is too long, also resulting in increased intraocular pressure. When large amounts of laser energy are applied, and the targets are too close to the pupil edge, papillary constriction can also occur. incomplete capsulotomies can also occur if the patient's head is not oriented properly to the femtosecond laser cutting plane, though this is rare and can be avoided with tilt compensation imaging software to ensure proper positioning of the laser during surgery, Dr Uy said.

Overall, laser-assisted surgery may make managing complications easier, but it is not a panacea, Dr Uy emphasised. 'Laser-assisted cataract surgery is not fool-proof. it makes vitreous loss management easier, but we still need careful planning, vigilance and good surgical principles to get successful outcomes.'