Minimizing Risks in Transconjunctival Vitrectomy Surgery
Preoperative, intraoperative and postoperative considerations
Abdhish R. Bhavsar, MD • Geoffrey G. Emerson, MD, PhD • M. Vaughn Emerson, MD • Jacob M. Jones, MD, PhD
Transconjunctival vitrectomy surgery has become commonplace today. The popularity of transconjunctival techniques stems from the potential for greater patient comfort, shorter opening and closing times, and finer instrumentation, which is desirable in certain circumstances. These methods, however, are associated with a different set of potential complications than traditional 20-gauge vitrectomy surgery. We discuss these complications here, together with potential strategies for risk mitigation. For convenience, we have subdivided the discussion into preoperative, intraoperative and postoperative considerations.
With regard to preoperative preparation, an important consideration is case selection; each surgeon should consider the advantages and disadvantages of 23-g or 25-g surgery vis-à-vis the surgical maneuvers required during each surgery.1,2 For example, the surgeon should be comfortable with the flexibility of the instruments, typically greater for 25-g instruments than 23-g. If the surgeon is not comfortable with the flexibility of the instruments during particular surgical maneuvers, then iatrogenic tears can occur, either due to direct trauma or excessive traction on epiretinal/fibrovascular membranes or traction on the vitreous attachments to the epiretinal/fibrovascular membranes. These complications can occur as a result of inadequate consideration of instrument movement and flexion at the fulcrum point (the sclerotomy site).
For vitreous hemorrhage, epiretinal membranes or macular holes, this flexibility may be tolerable for most surgeons. However, for complex tractional retinal detachments or intraocular foreign body removal, less flexibility and the greater stiffness characteristic of 20-g instruments may be helpful. Each surgeon should strongly consider case selection in determining which gauge vitrectomy system to use.
Once the decision has been made to proceed with transconjunctival surgery, attention should be given to pre-operative preparation of the eye for surgery, including anesthesia type and ocular surface preparation. Immobilization of the eye is ideal and can be achieved most commonly by retrobulbar anesthetic block with a mixture of 2% lidocaine and 0.75% bupivicaine (with or without hyaluronidase). On occasion, some patients with claustrophobia or anxiety may require general anesthesia. If there is inadequate akinesia, surgical maneuvers can be more difficult. When the globe moves, the instruments within the vitreous cavity move, and the surgeon is less likely to be able to control movement of the eye with a smaller-gauge instrument. This inability can be particularly problematic when operating on the surface of the retina during epiretinal membrane dissection or internal limiting membrane dissection.
A lack of akinesia can be easily addressed by supplementing the block with superior or inferior peribulbar or inferior retrobulbar lidocaine or bupivicaine. This application helps to minimize the risks that are associated with spontaneous ocular movement.
The preparation of the ocular surface deserves particular attention because the surgical incisions pass through the conjunctiva. First, we would recommend thoroughly treating ocular surface disease, such as blepharitis, prior to surgery. Second, we would recommend preparing the conjunctival surface with 5% povidone-iodine. At our institution, we place a drop of povidone-iodine on the conjunctival surface at the time of the retrobulbar block. Then during the preparation, while the lids and lashes are being scrubbed with povidone-iodine, another drop is placed on the conjunctival surface. The first author (ARB) also swipes the perilimbal conjunctiva with a cotton-tipped applicator soaked with 5% povidone-iodine just prior to starting the surgery.
We are careful to isolate the lid margin and lashes beneath the surgical drape when placing the speculum, such that the drape folds over and is posterior to the eyelid and eyelashes (Figure 1). One of us (ARB) prefers to have the eyelashes trimmed during the prep prior to surgery to help prevent the lashes from crossing the path of the instruments in case they are not completely isolated by the surgical drape.
Figure 1. Draping technique with 3M 1060 surgical drape placed such that the eyelid margins and lashes are isolated from the surgical field. REPRINTED WITH PERMISSION FROM BHAVSAR AR. VITRECTOMY SURGERY. IN: BHAVSAR AR, ED. RETINA AND VITREOUS SURGERY. PHILADELPHIA, PA: SAUNDERS/ELSEVIER; 2009:15-50.
The first step in transconjunctival vitrectomy surgery involves the creation of sclerotomies. We prefer to displace the conjunctiva anteriorly by several millimeters to the point of the desired sclerotomy location. Then, the sclerotomy is created using the trocar cannula with a biplanar entry, tangential to the sclera at first and then perpendicularly thereafter to create a self-sealing incision, as much as is possible.
The concept behind displacing the conjunctiva anteriorly is that it allows the conjunctiva to retract after the cannula is removed and thus does not permit a direct connection between the ocular surface and the sclerotomy. In experimental models of scleral incisions comparing 20-, 23- and 25-g sclerotomies, sutureless incisions (23-g and 25-g) were found to allow entry of ocular surface fluid.3 Thus, isolating the sclerotomy from the conjunctival entry by displacing the conjunctiva may help to minimize risk.
Postoperative hypotony (intraocular pressure <5 mm Hg) with or without wound leak has been reported in both 25-g and 23-g cases and occurs in up to 25% of 25-g cases4-9 and up to 6.5% of 23-g cases.8-14 Creating a self-sealing sclerotomy incision by employing an oblique or biplanar entry, as described above, helps to reduce the risk of postoperative hypotony and potentially endophthalmitis.15-19,28
Observing the infusion cannula tip and shaft directly in the vitreous, once they are placed through the trans-scleral cannula and before starting the infusion, is critical. Because the entry is angled, it is possible for the infusion cannula to be located in the suprachoroidal space or subretinal space. If the infusion is turned on while located in those spaces, it can create a retinal detachment, choroidal detachment or choroidal hemorrhage. If those complications occur, the infusion should be stopped immediately, and the infusion and sclerotomy cannulas should be removed from the eye and re-established via another sclerotomy location.
During the vitrectomy, the infusion line should be secured externally to the surgical drape with a steristrip to at least provide some security to prevent inadvertent withdrawal of the cannula from the eye. We continuously monitor the position of the infusion cannula during surgery to ensure that it has not been displaced from the sclerotomy. This process is particularly important when scleral depression is being performed during the vitrectomy. Even a small movement can displace the infusion cannula and result in sub-retinal or suprachoroidal fluid infusion.
If the infusion cannula is dislodged, sudden hypotony with choroidal detachment or hemorrhage is possible.20 In this case, prompt repressurization of the globe is necessary. This can be achieved by placing the infusion cannula in another patent sclerotomy port or by using a 30-g needle, injecting through the pars plana with balanced salt solution in the fluid-filled eye or with sterile air in the air-filled eye.
The surgical maneuvers during vitrectomy require attention to the angle of entry and exit from the cannulas. We would recommend inserting and removing the instruments at the same angle at which the cannula is placed. Doing so avoids stretching the sclerotomy during the entry and exit of each instrument. In addition, it avoids snagging the instrument on the cannula and inadvertently removing the cannula from the eye when an instrument is removed from the sclerotomy.
When instruments are removed from the sclerotomies for longer than a simple instrument exchange, the appropriate plugs should be placed to secure fluid flow or airflow through the cannulas. Doing this prevents unnecessary hypotony due to excessive fluid flow or airflow through the sclerotomies. Control of the IOP during vitrectomy is of great importance because sudden hypotony during vitrectomy can cause choroidal detachment or choroidal hemorrhage. When removing the cannula plugs, we recommend stabilizing the cannula itself with a forceps, ie, a 0.12 forceps, to prevent the cannula from being removed from the sclerotomy when the plug is removed (Figures 2 and 3).
Figure 2. Grasping the 23-g cannula with a .12 forceps prior to removing the plug.
Figure 3. Removal of the 23 cannula plug while still stabilizing the cannula itself with a 0.12 forceps.
The first author (ARB) prefers always to perform a complete vitrectomy, including peripheral vitreous removal. This practice may theoretically reduce postoperative retinal tears and detachment by decreasing potential vitreous traction and may reduce the risk of postoperative endophthalmitis. The central concept revolves around the increased risk of vitreous incarceration in the sclerotomy in the absence of a complete peripheral vitrectomy.21,22 This in turn serves as a wick that stents the sclerotomy open, potentially allowing a direct route for bacteria into the peripheral vitreous.23
The incidence of retinal tears with small-gauge vitrectomy surgery has been reported to be up to 24%.24 One way to minimize retinal tears is to reduce unnecessary traction on the vitreous while cutting with the vitrectomy handpiece. Care should also be taken to thoroughly trim the vitreous in the areas of the instrument cannulas to prevent vitreous entanglement when inserting or removing instrumentation. Equally, or perhaps more, important is the identification of retinal tears during surgery by indirect ophthalmoscopy or direct visualization with scleral depression, followed by treatment with cryoretinopexy or laser retinopexy.29
At the end of all of our 23- or 25-gauge vitrectomies, we perform a partial to full fluid-air exchange, and we leave the eye with either an air or gas fill. Doing so theoretically allows the surface tension of the bubble inside the eye to seal the sclerotomies. A leaky wound that is not “fluid-tight” may be “gas-tight” due to the surface tension of the gas bubble. This condition may in turn lead to less hypotony and perhaps a lower risk of endophthalmitis. In one meta-analysis of endophthalmitis in 25-g cases, out of 22 patients with endophthalmitis, 19 eyes were left fluid-filled at the end of the vitrectomy and did not undergo fluid-air exchange.25 Thus, it seems that fluid-air exchange and leaving the eye at least partly filled with air or gas can potentially reduce the risk of endophthalmitis.
If there is any leakage from any of the sclerotomies, gentle massage of the sclerotomy with a cotton-tipped applicator may reduce leakage. If there is still leakage, then we recommend placing a single 8.0 or 7.0 Vicryl suture through the sclerotomy to close it. Suture closure of sclerotomies may also be prudent when the patient is deemed likely to manipulate the eye extensively after surgery, has a severe cough, or has a history of postoperative nausea and vomiting. Suturing in such cases avoids the risk of postoperative hyptony, choroidal detachment or choroidal hemorrhage.
We also perform subconjunctival injections of dexamethasone and antibiotics (typically cefazolin) 0.5 cc each, adjacent and posterior to the sclerotomies, to balloon the conjunctiva over the sclerotomies. These injections can potentially maintain any vitreous wick in the subconjunctival space by “retracting” the wick away from the ocular surface and displacing the conjunctiva outward, thereby preventing any vitreous wick from connecting to the exterior conjunctiva.26
At the conclusion of the surgery, the primary author (ARB) places a drop of 5% povidone-iodine on the ocular surface to reduce the risk of endophthalmitis.27
The main postoperative concern inherent in smaller-gauge surgery without sutures is patency or leakage through the sclerotomies. If the eye is profoundly hypotonous postoperatively (ie, an IOP of 5 mm Hg or less), we would recommend considering repressurization of the eye with either sterile air or gas injected through the pars plana with a 30-g needle.
If the eye is still hypotonous and there is leakage from one or more of the sclerotomies, we recommend returning to the operating room, repressurizing the eye, and placing 8-0 or 7-0 Vicryl sutures through the leaking sclerotomies. This process will help to reduce the risk of postoperative hypotony or choroidal detachment or hemorrhage.
Transconjunctival/smaller-gauge vitrectomy surgery can be performed safely when the surgeon is well prepared to minimize the potential risks associated with the surgery. We hope the considerations described above will help you to minimize the risks associated with your vitrectomy surgeries. RP
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|Abdhish R. Bhavsar, MD, Geoffrey G. Emerson, MD, PhD, M. Vaughn Emerson, MD, and Jacob M. Jones, MD, PhD, practice with Retina Center of Minnesota. The authors report no financial interest in any products mentioned in this article. Dr. Bhavsar can be reached via e-mail at email@example.com.|