Eyeworld

EW NEWS & OPINION 17 O n very rare occasions, an- terior chamber depth is inadequate to allow for cataract surgery to be safely performed. Ancil- lary measures, including digital ocular massage and intravenous administration of mannitol, in com- bination with the use of a viscoadap- tive OVD, are generally sufficient to manage the "crowded anterior seg- ment." However, should anterior chamber depth be inadequate to perform capsulorhexis and other stages of surgery, the cataract sur- geon may need to consider a very limited pars plana vitrectomy prior to cataract surgery. In this infre- quent scenario, the surgeon would note that the globe becomes "rock hard" after anterior chamber instilla- tion of a viscoadaptive OVD, yet the chamber depth remains inadequate for cataract surgery. Intumescent mature cataract and anterior seg- ment microphthalmos are typical causes. Although the anterior cham- ber may be shallow in cases of dif- fuse zonulopathy, the chamber will often deepen on administration of an OVD. The surgical technique involves making a single pars plana entry with a disposable MVR blade, gener- ally 3.5 mm posterior to the limbus. The unsleeved vitrectomy probe is aimed toward the middle of the globe and angled posteriorly in order to avoid damage to the poste- rior lens capsule; no infusion is nec- essary. High-speed cut rate and low vacuum setting is carried out for only a few seconds, the probe care- fully removed, and the anterior chamber deepened with additional OVD. In this manner, the vitreous volume is reduced, the anterior chamber deepened, and ocular hy- potony is avoided. Varying with the nature of the sclerotomy, suture clo- sure may be necessary at this time. The practice of pars plana vitre- ous aspiration at cataract surgery in this clinical scenario has been de- scribed previously. 1 In fact, during the infancy of lens implant surgery, and before the advent of OVDs, not infrequently surgeons would employ pars plana needle aspiration of vitre- ous in order to create anterior cham- ber space for lens implantation. With the advent of automated vit- rectomy, the technique changed and was eventually published in the peer-reviewed literature by David F. Chang, M.D. 2 Two following cases are illustrative. Case 1 A 69-year-old male was referred fol- lowing an attack of acute angle-clo- sure glaucoma. An intumescent, mature cataract ensued and cataract surgery was attempted. However, at surgery the chamber was noted to be extraordinarily shallow and the pro- cedure aborted prior to anterior cap- sulotomy. Upon examination one could note a prior superior iridectomy, posterior synechiae with an irregu- lar, poorly dilating pupil, and an as- sociated pupillary membrane (Figure 1). The cataract was fully white, pre- cluding examination of the posterior pole. However, the patient had brisk two-point light discrimination and grossly normal color perception. B- scan ultrasonography revealed a nor- mal posterior segment. The fellow eye was pseudophakic, but otherwise normal to examination. At surgery the patient received peribulbar injection anesthesia, digi- tal ocular massage, and 50 grams of intravenous mannitol. Despite these maneuvers, instillation of a small amount of DisCoVisc (Alcon, Fort Worth, Texas) via a paracentesis was accompanied by marked elevation of IOP, yet chamber workspace was in- adequate. As described, an auto- mated pars plana vitreous aspiration was performed and surgery com- pleted without complication. Sur- gery was complex in that it was necessary to perform synechiolyis, pupil membranectomy, pupil stretch, and trypan blue capsule staining. As the cataract was intu- mescent, copious liquefied white cortical material effused upon initia- tion of the capsulorhexis, but the capsulotomy was safely completed in two stages after aspirating the ma- terial (Figure 2). It is quite likely that by allowing the anterior capsule to flatten with OVD, the vitrectomy prevented uncontrolled tearing of the anterior capsule, in the manner of the "Argentinian flag sign". The post-op course was routine and the patient returned to normal visual function. However, owing to pre-existing synechiae, the pupil re- mained slightly irregular post-op. Case 2 A 68-year-old female came under care in 2005 and was noted to have asymmetric anterior chamber depths, with the LE noted to be par- ticularly shallow. This eye had a pre- vious laser peripheral iridotomy. Moreover, she had pseudoexfolia- tion, although there was no evi- dence of phacodonesis. Gradually, the involved eye developed a visu- ally significant cataract. Presurgical testing revealed an anterior chamber depth of less than 2.0 mm. At surgery the chamber could not be adequately deepened with ad- dition of DisCoVisc. Following ad- ministration of a small amount of subconjunctival anesthetic, a con- junctival peritomy was created and a limited automated pars plana vitrec- tomy performed as described above. Once completed, surgery was carried out routinely. Interestingly, there was no evidence of zonular weak- ness, although a capsular tension ring was placed prophylactically. by Samuel Masket, M.D., Basak Bostanci Ceran, M.D., and Nicole R. Fram, M.D. Vitrectomy prior to cataract removal for the "crowded anterior segment" E yes with very shallow anterior chambers come along every now and then. Most are anatomically small in the an- teroposterior dimension and carry hyper- opic refractive errors. The central anterior chambers of these eyes may be only a few corneal thicknesses deep, and their irises may be in apposition to the peripheral pos- terior cornea. Often they have had a pe- ripheral iridectomy already because they are anatomically predisposed to phakic pupillary block and angle closure glau- coma. Despite these obstacles, most of these eyes can undergo fairly routine cataract surgery with a few extra consider- ations—a little pre-op digital massage, the administration of a hyperosmotic agent, a carefully constructed cataract incision that prevents iris prolapse, and the judicious use of a highly retentive OVD. Every now and then, however, these relatively simple measures are not enough. Some times the patient has severe pain and an intraocular pressure of 60 mm Hg on presentation. The eye is in acute angle closure, or worse yet, phacomorphic or rubeotic angle closure. The anterior chamber may only be the depth of the pupil sphincter. In such eyes, there may be no anterior chamber into which to make a paracentesis. The iris may be against the posterior cornea. Once made, the iris prolapses immediately into the paracentesis incision. Forced entry with an OVD cannula only causes iris trauma. These are the eyes in which it might be necessary to perform a dry vitreous tap and make room in the posterior segment for the lens to drop back. It is a trick any cataract surgeon can learn. In their article, Drs. Masket, Ceran, and Fram describe their experience with the dry vitreous tap technique for the rare eye that presents with a very crowded anterior segment. Kevin Miller, M.D., complicated cataract cases editor Figure 1 Figure 2 Source: Samuel Masket, M.D. continued on page 18 December 2011 Complicated cataract cases Or view the video at www.eyeworld.org/ replay.php. 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