Eyeworld

EW RETINA 68 October 2016 by Steve Charles, MD scleral tunnel is not recommended. Creation of a scleral tunnel in a soft eye can result in suprachoroidal introduction of the cutter. Although some manufacturers have advocated 25-gauge vitrectomy for this setting, 23-gauge is a better choice because of tool stiffness in the context of topical anesthesia and eye move- ment. I use 25/27-gauge vitrectomy for all posterior vitrectomy cases, but these procedures are performed with a retrobulbar or occasionally peribulbar block. Visualization is essential for safe, effective anterior vitrectomy; triamcinolone particulate marking is ideal for this purpose. Triesence (Alcon, Fort Worth, Texas) is preser- vative-free. Many anterior segment sur- geons incorrectly think that vit- rectomy causes cystoid macular edema (CME); however, extensive pars plana posterior vitrectomy never causes CME, which refutes the vitreous removal hypothesis for CME causation. CME is associ- ated with anterior vitrectomy after capsule rupture in cataract surgery not because of vitreous removal but due to iris trauma from cellulose sponges, iris retractors and surgical manipulation. Cellulose sponges imbibe infusion fluid and liquid vit- reous, swell, and traumatize the iris as they are lifted out of the vitreous cavity. In addition, direct iris trauma occurs when they are used to test for vitreous. Sweeping the wound is also a dangerous maneuver; acute vitre- oretinal traction results from this maneuver. It is far safer to remove vitreous from the wound with the cutter. When capsule rupture occurs, the first step is to inject OVD be- fore removing the phaco probe to stabilize the anterior chamber and prevent lens material from moving posteriorly. A viscoelastic barrier is ideal for prevention of vitreous mo- bilization into a capsular defect and the phaco wound while removing remaining lens material and im- planting an intraocular lens. Posteri- or dislocation of lens material never damages the retina; inappropriate action by the surgeon is the real cause of retinal damage in this situ- ation. The phaco probe can give the i.e., retinal breaks. The lowest effec- tive aspiration flow rate or vacuum should be used to reduce non-pulsa- tile vitreoretinal traction. Technique is crucial as well; the vitreous cutter should never be pulled back while vitreous is engaged; the safest tech- nique is "continuous engage and advance," a term I coined. Infusion should always be used for anterior vitrectomy; so-called "dry vitrectomy" inherently pro- duces hypotony, scleral infolding often misinterpreted as choroidal effusion, miosis, and occasionally, catastrophic suprachoroidal hemor- rhage. The infusion should always be separated from the vitreous cutter incision; the infusion sleeve causes turbulence, which reduces vitrec- tomy efficiency as well as causes damage to the corneal endotheli- um. The vitreous cutter should be placed through one sideport incision or the pars plana and a 23-gauge angulated infusion cannula or an- terior chamber maintainer through another sideport; the cutter should never be placed through the phaco incision. Separating the cutter from the infusion reduces turbulence, endothelial damage, iris trauma, and is more efficient with respect to removing vitreous. Although many surgeons are not comfortable with pars plana vitrectomy, this approach removes all vitreous from the anterior segment without damage to the corneal endothelium or iris, eliminates vitreous to the wounds, and is effective at removing residual cortex. If a pars plana vitrectomy ap- proach is utilized, the phaco wound should be sutured to prevent iris prolapse. Although trocar-cannula systems have revolutionized suture- less, transconjunctival vitreoretinal surgery, they are unnecessary for pars plana approaches to anterior vitrectomy. The primary purpose of trocar-cannula systems is to main- tain misalignment of the conjuncti- va that was intentionally displaced from the sclerotomy site and allow tool exchange without wound damage. Neither of these advantages is relevant to the cataract surgery setting. It is better to make a small circumferential conjunctival incision 3.5 mm posterior to the limbus and enter with a 23-gauge MVR blade; a retinal traction. Anterior vitrectomy is never "simple," as some surgeons have incorrectly stated. Anterior vit- rectomy is performed in close prox- imity to the vitreous base, a zone of permanent adherence of vitreous to peripheral retina with 1/100 the tensile strength of posterior retina. The majority of post-cataract surgery retinal breaks occur at the posterior edge of the vitreous base. Aspirating liquid vitreous without a cutter is hazardous, liquid vitreous is illusory, severe vitreoretinal traction always occurs from pulling on the collagen fiber matrix. Vitreous cutters are far safer than cellulose sponge vitrectomy. Cellulose sponges should never be used to test for vitreous during cataract surgery or penetrating ker- atoplasty or removal of vitreous at the site of traumatic corneal-scleral lacerations. Vitreous cutters must be used with the highest possible cut- ting rates to minimize pulsatile vit- reoretinal traction. I coined the term "pulse flow" to describe the volume of vitreous that goes through the cutter port with each open/close cy- cle. High cutting rates produce lower pulse flows, less acceleration, and therefore less force on the vitreous. High cutting rates confine energy to the region near the port while lower cutting rates produce remote effects, Tips for avoiding a retinal break or detachment after cataract surgery I n spite of extraordinary ad- vancements in cataract surgery techniques and technology, rupture of the posterior capsule, posterior dislocation of lens material, and the need for anterior vitrectomy still occur at a substantial rate. It is likely that femtosecond laser-assisted cataract surgery will reduce the incidence of capsular rupture, but widespread adoption will take years. The relatively low in- cidence of capsular rupture can pro- duce the unintended consequence of poor preparation and even hasty, unwise actions. Anterior vitrectomy began with the pioneering work of David Kasner in the late 1960s, using cellulose sponges and scissors to remove anterior vitreous. This approach was based on the concept that the critical problem was vitreous incarceration in the cataract wound. Unfortunately, it was not recognized that severe intraoperative vitreoret- inal traction is inherent in cellulose sponge anterior vitrectomy. Lifting the sponge and adherent vitreous to enable scissors cutting as well as wicking cause marked acute vitreo- Management of capsule rupture at cataract surgery Ruptured capsule at cataract surgery Source: Byron Wood, Vitreous Microsurgery, Fifth Edition

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