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Anterior vitrectomy can ensure better outcomes after complicated cataract surgery


Surgeons must recognize and control damage early to reduce the likelihood of postoperative sequelae.


Issue: October 10, 2012

ByLisa Brothers Arbisser

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Cataract surgery has advanced to new levels, with smaller incisions, less postoperative iatrogenic astigmatism, quicker visual recovery, fewer postoperative restrictions and improved overall quality of vision. The IOLs have also largely improved, with premium lenses offering spectacle independence for both distance and near in most daily activities. Additionally, newer laser techniques to assist in reproducible anterior capsulorrhexis and the cataract extraction process have taken cataract surgery to even greater heights. 


Although these advances have greatly improved the quality of cataract surgery, potential complications continue to exist. One such complication that the surgeon and the operating room staff are not usually prepared to handle in a quick and efficient manner is the inadvertent opening of the posterior capsule with vitreous access to the anterior segment of the eye. Proper surgical management of capsular tear and its associated issues is of great importance to the overall postoperative visual outcome for the patient.


In this column, Arbisser describes an efficient stepwise approach to using anterior vitrectomy to ensure better visual outcomes for our patients.


Thomas John, MD


OSN Surgical Maneuvers Editor


 

Lisa Brothers Arbisser

Vitreous loss is inevitable. Given the volume of cataract surgery and the variety of pathology presented by the human eye, even in the best of hands there will be some rate of complications involving loss of the integrity of the capsular or zonular structure. Our obligation to our patients is to prevent vitreous loss when predictable and minimize the impact of its consequences when possible.


Complications can be placed into three categories: a broken capsule or loss of zonular integrity with an intact vitreous face, vitreous prolapse (defined as vitreous within the confines of the anterior chamber), and vitreous loss through the incision. The likelihood of postoperative sequelae increases significantly with each of these categories and motivates the surgeon to recognize and control damage at the earliest stage. The more vitreous traction we permit or cause and the more we fail to prevent inflammation, the lower the chance of an ideal outcome we offer our patient.


Surgical technique


A valuable tool whenever a broken hyaloid is suspected is Triesence (triamcinolone acetonide, Alcon). The particles adhere to the vitreous and not to viscoelastic. Instillation of this steroid diluted with balanced salt solution into the anterior chamber identifies vitreous prolapse like throwing a sheet over a ghost. Also, the drug has the therapeutic effect of reducing postoperative inflammation. 


Although anterior vitrectomy can be performed through a clear corneal or a pars plana approach, there are some absolute criteria we must follow. Whichever incision we choose, the instruments should be biaxial, with the irrigation separated from the vitrector. Because vitreous always follows a gradient from high to low pressure, if we want it to flow into the vitrector, irrigating at the tip will be counterproductive and fluid will tend to displace the vitreous body, necessitating that more be removed. The goal is to preserve as much of the vitreous structure as possible while removing any strands that have prolapsed into the anterior segment. Irrigation should always be through the side-port incision to encourage vitreous to remain posteriorly and keep higher pressure in the front of the eye. 


Whether the incision is clear corneal or scleral, it must snuggly fit the bare vitrector needle so vitreous cannot flow around it through a leaky incision. Default settings of irrigation in foot position 1, cutting in foot position 2, and then vacuum in foot position 3 must be confirmed to prevent followability and therefore traction. Always stay in foot position 2 (cutting) when moving the vitrector through vitreous to prevent inadvertent flow into the tip from causing traction. No actual vitreous removal will occur until foot position 3 is engaged. All machines have a manual override that switches the function of foot positions 2 and 3 so that vacuum can be applied without cutting to facilitate followability. This should only be employed when vitreous is no longer present, as in the removal of residual cortex. 


 

Figure 1. Use biaxial technique with irrigation through side-port and vitrector through another paracentesis sized to fit the bare vitrector shaft rather than the main clear corneal incision to obtain a closed system.

Images: Arbisser LB

 

Figure 2. Be sure to measure 3.5 mm back from the limbus with a caliper after creation of the peritomy in the quadrant convenient to the dominant hand to have a margin of safety within the pars plana.

 

 

Figure 3. The sclerotomy is made with the appropriately sized microvitreoretinal blade for the gauge of vitrector. Aim toward the center of the eye and visualize the tip within the pupil to confirm complete entry.

 

Figure 4. The irrigation is still placed in the side-port paracentesis and the vitrector, placed through the pars plana sclerotomy, is visualized in the pupil. The port should always be visible during vitreous removal.

 

 

Figure 5. A double-bite mattress or X suture with 8-0 Vicryl closes the sclerotomy and can be used to close Tenon’s and conjunctiva over the incision as well.

 

 

Figure 6. Triesence particulate identification of vitreous in a cadaver eye.

 

 

Figure 7. Sutureless 23- or 25-gauge trocar system initially makes a scleral tunnel parallel to the limbus with a non-coincident incision in the conjunctiva and sclera.

 

 

Figure 8. The cannula is rotated to enter sclera in a perpendicular fashion. This creates a watertight sutureless incision upon removal in almost all cases.

 

The cut rate should be at its highest setting available, 400 to 5,000 cuts per minute, depending on the machine. The aspiration flow rate is kept low: 20 cc per minute for 20-gauge instrumentation and 15 cc per minute for 23-gauge. The lowest vacuum that provides removal of vitreous should be employed, usually 150 mm Hg for 20-gauge and 350 mm Hg for 23-gauge, depending on how much of a viscoelastic-filled environment one is working in. I recommend this be on a panel or fixed setting rather than linear because the surgeon can then be anywhere in foot position 3, even pedal to the metal, without allowing too much vacuum. The bottle height is then balanced with the level of vacuum needed to get action so as to maintain a normotensive eye, usually around 80 cm for a 23-gauge cannula or chamber maintainer.


If a clear corneal approach is employed, tilt the vitrector down below the posterior capsule in order to pull vitreous back to the posterior segment. Remove or amputate anterior-posterior connections of any prolapsed vitreous. It can be difficult to fully amputate a flat sheet of vitreous or a strand to the incision that is adherent to the iris with this approach. There is a tendency to call more vitreous forward while trying to remove the vitreous that is already forward. Once we reach an endpoint with the maneuver, the pressure is lowest in the anterior segment, which encourages vitreous to present again on subsequent maneuvers. For these reasons a corneal incision may not be the optimal choice, although it is mandatory when there is no view available through the pupil and best when the surgeon is unfamiliar with the pars plana approach.


The reasons for using a pars plana sclerotomy for vitrectomy are that it leaves the lowest pressure posteriorly and allows subsequent maneuvers while minimizing re-presentation, it is the most efficient because it calls the vitreous home, and it will not unzip the zonules when vitreous presents around the lens equator by calling more vitreous forward through the defect. 


Pars plana approach


Finally, the pars plana approach facilitates amputation of the vitreous within incisions. Although we were taught to use a sweep from the side-port incision to drag entrapped vitreous away, this actually creates more traction on the connection through the pupil rather than efficiently freeing the vitreous from incarceration in the wound. I strongly discourage this practice. The preferred technique is particulate identification and sharp cutting or ideally using a vitrector to amputate connections posteriorly at the pupil margin. 


Once the vitreous sheet either retracts to the posterior segment or is severed from the vitreous within the wound, it is safe to remove residual vitreous from the incision with a cellulose sponge. Sponges should never be used to remove vitreous that is still attached posteriorly because they absorb vitreous strands, causing traction and, upon contact with iris tissue, inflammation. Anytime you touch a sponge to the incision, have scissors ready in the other hand so that, should you discover vitreous, you can cut it without lifting or stretching the strands. Immediately cut off the vitreous at the plane of the sclera so that you do not pull it forward out of the wound. Then you may address the vitreous in the optimal manner.


The pars plana incision is made by measuring 3.5 mm behind the limbus in a quadrant (away from ciliary arteries, vessels and muscle insertions) under a small fornix-based conjunctival flap. The microvitreoretinal blade is inserted, aiming toward the geometric center of the globe. Ideally it is visualized within the pupillary space, as is the vitrector, which follows. Upon completion of the vitrectomy, the incision should be free of vitreous incarceration and, if a 20-gauge vitrector was employed, sutured with a double-bite mattress stitch of 8-0 Vicryl or the surgeon’s preferred closure. 


If a 23-gauge trocar cannula system is to be used, a true sutureless incision can be performed. The eye must be firm and intact, with closed or sutured incisions. Pull the conjunctiva away from the site of puncture 3.5 mm back from the limbus and initiate a partial-thickness scleral tunnel with the trocar parallel to the limbus. Travel 2 mm, then turn the device perpendicular to the sclera and puncture the sclera in the direction of the optic nerve, driving the cannula trocar system through the eye wall. Once the trocar is in place, remove the microvitreoretinal blade and leave the seated cannula for the vitrector’s insertion. If vitreous has been lost, you will not be able to close the incisions, even with sutures, so a direct microvitreoretinal entry with suturing would be safest. Because the trocar cannula protrudes into the vitreous cavity, the vitrector probe never gets close to the retinal surface, as it does when inserted through a bare sclerotomy. This design provides a margin of safety upon entry and exit. As they become sharper and require less pressure for entry, trocars will become the entry of choice.


Effectively dealing with crisis is, more often than not, a matter of having prepared for it. We must remain ever mindful of not causing intraoperative or allowing postoperative vitreous traction. I hope this column will help you achieve the excellent visual results that are still obtainable in these challenging cases.