Steve Charles, MD
In spite of extraordinary advancements 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 possible that femtosecond laser–assisted cataract surgery will reduce the incidence of capsule rupture, but widespread adoption is uncertain. The relatively low incidence of capsule rupture can produce the unintended consequence of poor preparation and even hasty, ill-advised 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 causing cystoid macular edema (CME) and retinal detachment. Unfortunately, it was not recognized that marked intraoperative vitreoretinal traction is inherent with cellulose sponge anterior vitrectomy. Lifting the sponge and adherent vitreous to enable scissors cutting caused wicking and marked acute vitreoretinal traction (Figure 65-1). Anterior vitrectomy is never “simple” as some surgeons have incorrectly stated. Anterior vitrectomy is performed in close proximity to the vitreous base, a zone of permanent vitreous adherence to peripheral retina with 1/100 the tensile strength of more posteriorly located retina. The majority of retinal breaks following cataract surgery occur at the posterior edge of the vitreous base. Aspirating liquid vitreous without a cutter is hazardous. Liquid vitreous is illusory, and severe vitreoretinal traction always results from pulling on the collagen fiber matrix.
Vitreous cutters are far safer than cellulose sponge vitrectomy methods. Cellulose sponges should never be used to test for vitreous during cataract surgery or penetrating keratoplasty or at the site of traumatic corneal-scleral lacerations. Vitreous cutters must be used with the highest possible cutting rates to minimize pulsatile vitreoretinal traction. The author coined the term pulse flow to describe the volume of vitreous that goes through the cutter port with each open/close cycle. High cutting rates produce lower pulse flows, and therefore less acceleration force on the vitreous. High cutting rates confine energy to regions near the port while lower cutting rates produce remote effects that can result in retinal breaks. The lowest effective aspiration flow rate or vacuum should be used to reduce nonpulsatile vitreoretinal traction. Technique is crucial as well, and the vitreous cutter should never be pulled back while vitreous is still engaged. The safest technique is continuous engage and advance, a term coined by the author.
Infusion should always be used for anterior vitrectomy. So-called dry vitrectomy without paired infusion inherently produces hypotony, scleral infolding (often misinterpreted as choroidal effusion), miosis, and occasionally, catastrophic suprachoroidal hemorrhage. The infusion should always be separated from the vitreous cutter incision. The coaxial infusion sleeve causes fluid turbulence, which reduces vitrectomy efficiency and may cause damage to the corneal endothelium. The vitreous cutter should be placed through one side-port incision or the pars plana and a 23-gauge angulated infusion cannula or anterior chamber maintainer is placed through another side port (Figure 65-2). The vitreous cutter should never be placed through the phaco incision. Separating the cutter from the infusion reduces turbulence, endothelial damage, and iris trauma and removes vitreous more efficiently. Although many cataract surgeons are not comfortable with pars plana anterior vitrectomy, this approach has several advantages. It removes all vitreous from the anterior segment with minimal damage to the corneal endothelium or iris, eliminates vitreous to the wounds, and is effective at removing residual cortex. However, care must be taken to avoid damaging the posterior capsule. If a pars plana vitrectomy approach is used, the phaco wound may need to be sutured to prevent iris prolapse. Although trocar-cannula systems have revolutionized sutureless, transconjunctival posterior vitreoretinal surgery, they are unnecessary for pars plana approaches for anterior vitrectomy. The primary purpose of trocar-cannula systems is to maintain misalignment of the conjunctiva that was intentionally displaced from the sclerotomy site to allow instrument exchange without wound damage. Neither of these advantages is relevant to the anterior vitrectomy setting. It is better to make a small circumferential conjunctival incision 3.5 mm posterior to the limbus and enter with a 23-gauge microvitreoretinal blade; a scleral tunnel is not recommended. Creation of a scleral tunnel in a soft eye can result in suprachoroidal or subretinal introduction of the cutter. Although some manufacturers have advocated 25-/27-gauge vitrectomy for this setting, 23- or 25-gauge is a better choice because of greater shaft stiffness in the context of topical anesthesia and the high force and amplitude of saccadic eye movement. The author uses 25-/27-gauge vitrectomy for all posterior vitrectomy cases, but these procedures are performed with a retrobulbar or rarely general anesthesia, always with akinesia.
Figure 65-1. Cellulose sponges should never be used to remove or test for vitreous; they cause unavoidable acute vitreoretinal traction because of wicking and lifting to cut.
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