Article Date: 11/1/2008

Vitrectomy Tips in Diabetics

Vitrectomy Tips in Diabetics

These practical strategies can minimize complications and improve outcomes.

MARC J. SPIRN, MD · CARL D. REGILLO, MD

In the United States, 8% of the population has diabetes, accounting for approximately 23.6 million individuals.1 Even as the number of individuals diagnosed with diabetes continues to grow, an estimated 24% of diabetic patients live unknowingly with the disease. With this increase in the number of patients comes a concomitant increase in diabetic complications, including diabetic retinopathy, a frequent cause of vision loss. With tight glycemic control, both worsening of diabetic retinopathy and vision loss can be prevented. However, when blood glucose levels are poorly controlled for many years, patients may present with macular edema or proliferative diabetic retinopathy (PDR) with or without tractional changes. Depending on the clinical situation, laser photocoagulation (focal/grid or panretinal) or pharmacologic intervention may be warranted. When these options fail or are not possible, surgical intervention may then be indicated.

The decision to perform ocular surgery in a diabetic patient is not always cut and dry. However, once a decision to operate has been made, a detailed preoperative and perioperative plan can enhance patient outcomes. Considerations include surgical gauge, whether preoperative pharmacotherapy or laser treatment is warranted, and what surgical technique to pursue. In this article, we offer tips to enhance operative outcomes in diabetic patients.

Marc J. Spirn, MD is an attending surgeon at Wills Eye Institute and instructor of ophthalmology at Thomas Jefferson University, both in Philadelphia. Carl D. Regillo, MD, is director of clinical retina research at Wills and professor of ophthalmology at Jefferson. Dr. Regillo reports minimal financial interest in Alcon as a consultant; Dr. Spirn reports no financial interest in any products mentioned here. Dr. Spirn can be reached via e-mail at spirnm01@yahoo.com.

PREOPERATIVE PREPARATION

Preoperatively, important considerations include maximizing the patient's ocular and systemic health. Whenever possible, each patient should receive a thorough evaluation from his or her primary care physician. Specific attention should be paid to renal status, electrolyte levels, and cardiovascular status, any of which may have an impact on anesthesia's willingness and ability to proceed with the case.

In patients with known high-risk PDR, preoperative panretinal photocoagulation (PRP) is likely to be beneficial. Goodart found that patients who underwent preoperative PRP had slightly better visual acuity and fewer macular detachments than patients without preoperative PRP.2 In addition, preoperative PRP may stabilize neovascular fronds, limiting intraoperative bleeding and decreasing the likelihood of tears when lifting the hyaloid. In patients with vitreous hemorrhage without concomitant tractional changes, injection of anti-vascular endothelial growth factor (VEGF) agents, such as bevacizumab (Avastin, Genentech), may promote neovascular regression. Whether anti-VEGF agents decrease the need for pars plana vitrectomy (PPV) in cases of vitreous hemorrhage has yet to be determined.

The decision to use VEGF inhibitors preoperatively in the setting of tractional retinal detachments is complex and somewhat controversial.3-5 One impediment to repairing a tractional retinal detachment is the moderate to severe bleeding that can occur during the repair. Preoperative injection of anti-VEGF agents shrinks neovascular fronds and may reduce intraoperative bleeding. In addition to shrinking the blood vessels, however, the VEGF inhibitors also can cause contraction of tissue, sometimes exacerbating the traction and increasing the degree of retinal detachment. For this reason, when we inject VEGF inhibitors preoperatively, we prefer to inject no more than 1 week prior to surgery, with the ideal time frame being 3 to 7 days prior to surgery. This time frame appears to enable neovascular regression while limiting fibrovascular contraction.

One additional consideration is whether or not to include dextrose in the infusion bottle. For phakic diabetic patients, adding dextrose to the balanced salt solution infusion may prevent cataractagenesis. In pseudophakic patients, however, this is not necessary.

CHOOSING THE GAUGE

When the day of surgery arrives and the patient has been optimized preoperatively, the next significant decision involves what gauge instrumentation to use. Of the 3 available gauges — 20, 23, and 25 — each has its advantages and limitations.

Both 23-g and 25-g instrumentation allow for transconjunctival, sutureless vitrectomy, which enhances patient postoperative comfort, reduces postoperative astigmatism, and often shortens operative times compared to traditional 20-g techniques.6,7 The transconjunctival approach may be particularly beneficial in patients where minimizing conjunctival scarring is paramount, such as in patients with advanced glaucoma or in patients who have had multiple prior surgeries.

Patient characteristics may influence one's decision to choose 23-g vs 25-g instruments. In nearly all cases, optimal outcomes can be achieved with 25-g instrumentation alone. However, the increased rigidity of 23-g instrumentation, especially the laser, may make 23-g preferable in diabetic cases when extensive laser is needed. Additionally, 23-g instrumentation is more suitable for clearing dense, or chronic, vitreous hemorrhages because its larger lumen is less likely to get clogged and more efficiently clears the blood.

We typically choose 25-g for simple macular edema cases and for re-ops, where less laser is necessary and where hypotony may be more likely with larger sclerotomies.8 In both instances, we prefer to bevel the sclerotomies to prevent postoperative hypotony. For most cases, including complex tractional retinal detachments, we usually choose 23-g instrumentation.

One of the main disadvantages of 23- and 25-g surgery is the somewhat limited available instrumentation. Instruments such as the membrane peeling cutting (MPC) scissors or fragmatome are not available in small sizes, and others, such as illuminated lasers, are subpar compared to their 20-g counterparts. The most worrisome concern of 23- and 25-g surgery is the suspected increased rate of endophthalmitis. In a retrospective series, Kunimoto et al. observed that 25-g surgery had an endophthalmitis rate 12 times greater than 20-g vitrectomy.9 This has yet to be proved in a prospective clinical trial. Postoperative hypotony may sometimes increase the risk of postoperative vitreous hemorrhage or hyphema, especially in eyes with PDR. When using 25- or 23-g surgery, we routinely use an air bubble at the conclusion of the case to insure good sclerotomy closure which should help to minimize the risk of postoperative hypotony and endophthalmitis.10

The main advantage of 20-g is that additional instruments are available. This is typically less important for simple membrane peels or when clearing a vitreous hemorrhage. In severe tractional retinal detachments, however, additional instruments may be beneficial. For example, self-illuminating instruments may facilitate bimanual surgery, and MPC scissors may ease segmentation, delamination, or en bloc dissection. If these instruments are needed, we usually prefer a hybrid technique where we use a 23-g infusion with 2 ports: a 23-g port and a 20-g port to accommodate the necessary instrument. Another option, if bimanual surgery is needed, is that one can always use an illuminated infusion canula or a fourth port with illumination (e.g., Tornambe Torpedo; Insight Instruments, Stuart, FL) and still use 25- or 23-g entry for the other 3 ports.

POSITIONING SCLEROTOMIES

Optimizing the superior sclerotomy placement can facilitate various aspects of the subsequent surgical procedure. When endolaser is unlikely, we typically orient the superior sclerotomies at 10 o'clock and 2 o'clock, which facilitates membrane peeling by limiting torque. When endolaser is likely to be necessary, we typically move the sclerotomies closer to the horizontals, placing them at 9:30 and 2:30. This allows better access to the superior retina when performing endolaser.

PARS PLANA VITRECTOMY FOR MACULAR EDEMA

Many recent studies have focused on the possible benefits of pars plana vitrectomy (PPV) for the treatment of diabetic macular edema (DME). It appears that, in select cases, PPV may improve DME and improve visual acuity, with potentially long-lasting effects.

In practice, we generally consider PPV for macular edema, either in cases that are refractory to focal/grid laser and pharmacologic intervention or in cases where a mechanical component is obvious. In cases with a mechanical component, lifting the hyaloid and peeling any epiretinal membrane is usually sufficient. In cases of preoperative posterior vitreous detachment, it may be helpful to also peel the internal limiting membrane (ILM).11-48 Intravitreal triamcinolone acetonide and indocyanine green are useful surgical adjuncts in many diabetic vitrectomy cases, not just those for refractory DME. Triamcinolone is an excellent tool for visualizing attached posterior hyaloids and can also be useful to peeling membranes. Either agent can be used to help peel ILM as needed. Furthermore, even if the primary purpose of the PPV is for another indication, we may also purposefully leave some triamcinolone in the vitreous cavity at the end of the case to minimize postoperative inflammation and macular edema. This is especially so if some edema was identified and extensive PRP was needed intraoperatively.

PARS PLANA VITRECTOMY FOR VITREOUS HEMORRHAGE

Other reasons to consider PPV in a diabetic patient are a nonclearing vitreous hemorrhage, a dense premacular hemorrhage with an intact posterior hyaloid, or a new dense vitreous hemorrhage in a patient's only seeing eye. As mentioned earlier, when treating vitreous hemorrhages, we place the sclerotomies closer to the horizontal meridian to optimize our ability to use laser superiorly. In addition, we prefer a curved, illuminated laser probe, as this minimizes the likelihood of lenticular touch and allows for unassisted depressed laser. In many cases of PDR, it is often advantageous to extend the PRP into the far periphery, even all the way to the ora, to help minimize the risk of neovascular complications postoperatively such as neovascular glaucoma.

One difficulty that may be encountered during these surgeries is the creation of a break around an area of neovascularization. Longstanding diabetics often have ischemic retinas which may be more prone to breaks than nondiabetic retinas. If one aspirates the posterior hyaloid near a tuft of NVE, a break can be created. To avoid this, care should be taken to circumscribe all areas of NVE with the vitrector to release all tangential vitreous traction on tufts of neovascularization elsewhere (NVE) before lifting the hyaloid. After carefully removing all gel from areas of NVE, the remainder of the hyaloid can be carefully lifted and peripheral dissection can take place.

PARS PLANA VITRECTOMY FOR TRACTIONAL RETINAL DETACHMENT

Tractional retinal detachments (TRDs) are among the most challenging cases performed by a vitreoretinal specialist. The primary goals of TRD repair is to remove all traction without creating a rhegmatogenous break. If this is possible, no tamponading agent is necessary, and visual recovery may be optimized.

Whenever we are performing a TRD repair, we pay special attention to the infusion pressure. Eyes with TRDs typically have compromised ocular blood flow and these cases are frequently longer than average, so minimizing high-infusion pressures, which may further limit ocular blood flow to the optic nerve or retina, is paramount. One frequent reason to increase the infusion pressure would be to tamponade a bleeding vessel. Preoperative use of anti-VEGF agents, which may help limit bleeding, may help decrease the amount of time spent at high pressures.

It is important to recognize that eyes with TRDs often have vitreous schisis. The first task when repairing a TRD, after performing the core vitrectomy, is to remove anteroposterior (A-P) traction of the gel to the fibrovascular proliferation. Because there are multiple layers of vitreous attachment (from vitreous schisis), multiple layers may need to be lysed to completely remove the traction. This traction is removed by cutting vitreous strands between the TRD and the periphery. Intravitreal triamcinolone may highlight residual strands making removal easier.

After removal of the A-P traction, we then focus on the tangential or circumferential traction. This can be accomplished by either segmenting or delaminating. The amount of segmentation and delamination is case-specific, and often some degree of both approaches are utilized. Whenever possible, however, we begin with segmentation, followed by delamination. Segmentation is easier with the 23- and 25-g cutters than the 20-g cutter because the cutter in the smaller-gauge instruments is closer to the tip than it is with 20-g. With 23- and 25-g instrumentation, segmentation can frequently be achieved using the cutter alone. On the Accurus machine (Alcon, Fort Worth, TX), we use the 3D mode for standard segmentation and the momentary mode when more delicate work is necessary. In instances where segmentation is not possible with smaller instrumentation alone, we either convert 1 port to 20-g to allow for the MPC scissors or we consider a bimanual technique.

After segmentation is complete, we frequently perform some degree of delamination. In some cases, if all circumferential traction is released, delamination may be unnecessary or of limited utility. In other cases, extensive delamination for residual traction may be necessary. There are many effective techniques by which to delaminate, including the use of horizontal scissors or a pick. One technique that we often employ is pressure delamination, where the head of the cutter is placed in the middle of the neovascular frond and gently depressed while aspirating. This causes any mobile aspects of the frond to fold into the cutter mouth like a flower folding in, while leaving underlying retina untouched. The cutter mouth is rotated 360° while performing this maneuver to allow all mobile areas access to the cutter mouth. In order for this technique to work, the neovascular frond must be slightly more mobile than the underlying retina. For that reason, we avoid this technique in cases of combined tractional/rhegmatogenous detachments.

In cases of difficult segmentation or delamination, it may be useful to consider bimanual surgery. This requires either a lighted instrument (e.g., a lighted pick in one hand with a forceps in the other) or a chandelier light (e.g., the Tornambe Torpedo). Both techniques have pros and cons. The chandelier emits a diffuse illumination but the lighting may be inadequate for detailed work. In addition, proper illumination requires that the chandelier be placed nearly perfectly, with little room for error. A lighted pick, conversely, gives good local illumination (for detailed work) but gives a limited field of view. One must be cautious when using a lighted pick not to "not see the forest for the trees." Nevertheless use of a chandelier light or an illuminated second instrument can prove invaluable for difficult delamination or segmentation.

After all A-P and tangential traction has been relieved, panretinal endolaser photocoagulation is applied, with care taken to avoid areas of subretinal fluid. Applying laser to areas of fluid can cause small retinal breaks, which may then necessitate the use of a tamponading agent. If all traction and laser is performed without creating a retinal break, we prefer to leave the eye fluid filled. However, if a break exists, then either gas or oil is necessary.

CONCLUSION

Performing vitreoretinal surgery in diabetic patients requires attention to detail and a systematic, logical approach. To optimize success, care must be taken in the preoperative assessment and treatment, as well as the intraoperative technique. When care is individualized to the patient, great success can be achieved and even the most difficult cases can have excellent outcomes. RP

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Retinal Physician, Issue: November 2008