Retina Today - Drop and Stop: The Dropping and the Dropped Nucleus (January 2011)

摘要

In 2009, the United Kingdom National Cataract Dataset of 55,567 cases reported overall posterior capsular rupture or vitreous loss rates of 1.92%.1 The British Ophthalmological Surveillance Unit (BOSU) reported 610 nuclear fragments displaced into the vitreous during 1 year in the United Kingdom, which is an incidence of between two and three per 1,000 operations, or approximately 0.3%.2 Although the frequencies of these are low, the complications of a dropped nucleus or vitreous loss may include raised intraocular pressure (IOP), uveitis, corneal edema, cystoid macular edema, and retinal detachment. When managed properly, however, the risk of further complications can be minimized, and the results can be as good as if it had never happened. This is reflected in the fact that two-thirds of all patients with a dropped nucleus between 2003 and 2004 had a final corrected vision of 6/12 or better.3 RISK FACTORSThe many publications investigating risk factors associated with posterior capsule rupture and vitreous loss have allowed surgeons to more accurately predict complications prior to surgery, plan more effectively, and counsel patients who are at risk.1 Early recognition of posterior capsular rupture or zonule dehiscence is key to preventing further problems as surgery progresses; it allows the surgeon to try to avoid certain maneuvers that can upset a precariously perched nucleus. Robert Osher, MD, carried out a series of experiments on cadaveric eyes to better understand what role vitreous contributes to the nucleus drifting downward.4 His findings suggest that in most cases the nucleus will sit supported by the vitreous if undisturbed. Older vitreous with more syneresis, however, will allow easier passage of the nucleus into the posterior segment. He also noted that high infusion pressures and pressure gradients have little bearing on the behavior of the nucleus, as the pressure is equal across the whole eye. The effect of high aspiration and post-occlusion surge due to high vacuum settings, however, can easily pull the vitreous supporting the nucleus toward the phaco tip, allowing the nucleus to drop. He also identified the turbulence created by phacoemulsification as a contributing factor in shifting vitreous support. ANTERIOR VITREOUS REMOVALIt is important to note that the underlying principle of complication management in any surgical setting must be to reduce the risk of further complications. Although the nucleus may sit on the vitreous, it may not be safe to deal with it in that position, as surgical maneuvers disrupt vitreous or cause retinal traction, increasing the risk of retinal complications. We therefore present a straightforward didactic plan for dealing with posterior capsular rupture and/or vitreous loss, together with an algorithm for handling dropped nuclear fragments and a view of how the two surgical teams, anterior and posterior, should proceed. The primary goal for the surgeon following early posterior capsular rupture or zonular dehiscence is to remove as much of the remaining nucleus as possible, but not without considering the risks that this involves. The most important intraoperative risk factor is vitreous traction. Continued irrigation alone following posterior capsular rupture is unlikely to cause the nucleus to drop, as demonstrated by Dr. Osher. Rather, it allows time to reassess the situation, move the nuclear fragments to a safe position if possible, and then remove the second instrument. An ophthalmic viscosurgical device (OVD), preferably dispersive, can then be injected to coat and tamponade the vitreous while also supporting the nucleus, allowing the phaco needle to be withdrawn without letting the vitreous surge forward toward the wound. This acts as a a??freeze-frame,a?? allowing one to assess the situation and plan further strategies. Performing bimanual vitrectomy through two paracenteses with a low bottle he