This article is from April 2006 and may contain outdated material.
Anterior vitrectomy is a crucial tool in the skill set of the anterior segment surgeon. Although a planned anterior vitrectomy may be performed in such settings as traumatic cataract removal or secondary IOL placement, this procedure is most often an unplanned —and unwelcome—addition to a cataract surgery. Even the most experienced surgeon will occasionally be faced with vitreous inadvertently prolapsing into the anterior segment. Thus, a surgeon’s comfort with basic anterior vitrectomy principles and techniques can defuse intraoperative stress and improve patient outcomes when complications involving the vitreous occur.
A basic knowledge of vitreous anatomy is helpful for understanding the intraoperative behavior of the vitreous. While the vitreous is 98 to 99 percent water, it also contains a network of fine collagen bundles suspended in coils of mucopolysaccharide hyaluronic acid. These collagen and hyaluronate components impart a gel-like consistency and a degree of elasticity to the vitreous. While a small amount of traction can be absorbed by the vitreous, a larger amount may be transferred through its collagen bundles to the posterior and peripheral retina, resulting in retinal tears and macular edema.1 The vitreous adheres most firmly to the retina at the optic nerve and at the vitreous base, an anatomic region that extends from approximately 2 millimeters anterior to 4 mm posterior to the ora serrata. Looser attachments also occur along the retinal vessels, in the perimacular region and in the periphery of the posterior lens capsule.
Vitreous Prolapse After Capsular Rupture
As most vitreous prolapse in cataract surgery occurs after a rupture of the posterior capsule, the most important step in management is to recognize that capsular rupture has occurred. Early recognition of a capsular tear may limit the size of the rupture and the amount of vitreous prolapse. Posterior capsular tears occur at the highest rate toward the end of phacoemulsification, when few pieces of nucleus remain in the bag; during irrigation and aspiration (I&A) of cortical material; or during capsular polishing.
Signs of capsular rupture may include a sudden deepening of the anterior chamber with sudden pupillary dilation as the hydrostatic pressures between the anterior and posterior chambers are abruptly equalized. The nucleus or remaining nuclear fragments may also move posteriorly through the capsular tear, especially with the influx of additional fluid from the phacoemulsification hand piece or I&A tip. The nuclear fragments may not flow as readily toward the phaco tip when the fluid currents no longer circulate through an enclosed bag and when vitreous clogs the aspiration port. Visualization of the tear may be impeded by residual nuclear or cortical material, but if the surgeon suspects that a tear has occurred, it probably has.
Several steps should immediately be taken to prevent enlargement of the tear and further vitreous prolapse.
First, phacoemulsification and aspiration should be stopped. The phaco or I&A hand piece should be maintained in the irrigation-only position in the anterior chamber to maintain a closed system with positive pressure that tamponades further prolapse.
Next, the anterior chamber should be filled with dispersive viscoelastic injected through the side port.
Then the phaco hand piece may be safely removed from the eye.
Coaxial or Bimanual?
Before beginning an anterior vitrectomy, the surgeon must first decide whether to use coaxial or bimanual irrigation and vitrectomy equipment. Most commercially available anterior vitrectors are designed to allow coaxial irrigation and vitreous cutting. The main advantage of this approach is the relative ease with which the system can be set up.
Separating the irrigation from the vitrector, however, has numerous advantages. In combined equipment, since the irrigation port is adjacent to the cutter port, placement of the tip through a capsular tear into the anterior vitreous may cause the tear to enlarge and more vitreous to come forward due to local turbulent flow and vitreous volume expansion from hydration. Separation of the irrigation line from the cutter, with limbal placement of a separate infusion cannula through an additional stab incision and with flow directed toward the anterior chamber angle, can reduce this phenomenon markedly.
If a bimanual approach is employed, an additional side port incision should be made to accommodate the vitrector. Use of the preexisting phaco wound, which is too large for the sleeveless vitrector, results in a less-stable anterior chamber as fluid, and possibly more vitreous, leak through the wound. The additional side port incision also allows greater access to the whole anterior chamber, as the irrigation cannula and the vitrector can be placed through either port.
Some surgeons advocate placing the vitrector through a stab incision made 3 mm posterior to the limbus through the pars plana using a microvitreoretinal blade. This approach offers increased access to the anterior vitreous and draws vitreous posteriorly during aspiration and cutting, away from the anterior chamber and the entry incisions. Concern about the possibility of a retinal tear with this approach, however, leads many surgeons to prefer a limbal incision for the vitrector.
Technique and Settings
The goals of anterior vitrectomy are to remove the vitreous from the anterior chamber, to clear any vitreous from the entry incisions and to allow an IOL to be placed. The bottle height should be greatly lowered, to 15 to 20 centimeters above the eye, before placing the infusion into the anterior chamber. After the vitrector is placed through the second side port incision, a closed system is established and the vitrectomy can begin.
If small nuclear fragments remain, removal of these fragments with the vitrector can be attempted by lowering the cut rate to 300 cuts per minute (cpm) and increasing the available vacuum. This allows the stiffer nuclear tissues to be engaged at low vacuum and then molded into the port, to be cut as the vacuum is increased. Larger fragments may need to be elevated into the anterior chamber with viscoelastic and removed manually. Remaining cortical fragments can be removed gently by turning off the cutter and using low vacuum to strip them from the bag with the cutter aspiration tip.
For vitreous removal, the cut rate should be set high, at 500 to 600 cpm, with low to moderate aspiration. A high cut speed for vitreous removal causes vitreous to flow continuously into the cutter, resulting in less pulsatile stress being placed on the retina. The vitrector is then placed through the capsular tear just below the capsule with the aspiration port facing up toward the cornea. The cutter should be maintained in a fairly central position and not moved peripherally beyond the plane of the iris root to avoid undue stress on the vitreous base. The vitreous is removed to a level just posterior to the capsule.
At the completion of mechanical vitrectomy, a manual Weck-Cel vitrectomy should be performed at all incision wounds to ensure that no vitreous remains incarcerated. Instillation of acetylcholine can also help identify any remaining vitreous in the anterior chamber by revealing irregular eddy currents around vitreous strands and by showing peaking of the miotic pupil (indicating vitreous remaining in an incision). The original phaco incision should be checked carefully to ensure it is watertight, and it should be sutured if any doubt exists. Because of the additional intraoperative manipulation of the vitreous and ocular structures, subconjunctival antibiotics and corticosteroids, such as 1 milligram each of cefazolin (Ancef) and bethamethasone acetate (Celestone), should be given at the end of the procedure.
1 Sebag, J. “Vitreous Biochemistry, Morphology, and Clinical Examination,” in Clinical Ophthalmology, Vol 3, ed. D. Thomas (Philadelphia: Lippincott Williams & Wilkins, 1998), 7–15.
Dr. Reeves is chief resident and Dr. Kim is associate professor of ophthalmology. Both are at Duke Eye Center in Durham, N.C.
Kenalog-Assisted Anterior Vitrectomy
Perhaps the most challenging aspect of removing vitreous from the anterior chamber is visualizing it. Because of the optical clarity of vitreous and its similarity to cortical fibers, a surgeon often must use indirect clues, such as peaking of the pupil or decreased aspiration efficiency with either the phacoemulsification or I&A hand pieces, to determine the presence and extent of vitreous prolapse. For this reason, Burke and colleagues have used triamcinolone acetonide (Kenalog) to assist in visualization of vitreous in the anterior chamber.1Kenalog particles “stain” the vitreous gel, making it readily visible for removal.
Intravitreal injection of Kenalog is used to treat macular edema associated with a range of retinal diseases.2 However, controversy exists as to whether the preservative supernatant should first be removed prior to injection. While some surgeons use Kenalog directly from the bottle and diluted with balanced saline solution (BSS), other surgeons, in order to minimize potential toxicity from the preservative, remove the preservative supernatant and replace it with saline before injecting Kenalog into the eye.
If the surgeon wants to remove the preservative from commercially packaged Kenalog, several methods have been described. One approach is to allow the Kenalog to settle to the bottom of the vial, then to decant the majority of the clear preservative solution from the top and replace it with saline.
The Kenalog particles can also be more thoroughly “washed” by using the following method described by Burke. First, a tuberculin syringe is used to draw 0.2 milliliters of Kenalog from a well-shaken bottle of Kenalog 40 mg/mL. Next, the needle is removed and replaced with a 5-micrometer syringe filter. The plunger of the tuberculin syringe is then depressed to force the Kenalog supernatant through the filter, trapping the Kenalog particles in the filter. The filter is then transferred to a 5 mL syringe containing BSS, which is then forced through the filter to wash the trapped Kenalog particles. Clean BSS is then drawn back up through the filter to yield Kenalog in solution in the syringe. This washing can be repeated to further rinse the particles, which can finally be suspended in 2 mL of BSS and injected through a cannula into the anterior chamber.
1 Burke, S. E. et al. J Cataract Refract Surg 2003;29:645–651.
2 McCuen, B. W. et al. Am J Ophthalmol 1981;91:785–788.