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Vitreous Surgery for Diabetic Retinopathy

Monica Rodriguez-Fontal John B. Kerrison

INTRODUCTION

Laser therapy and tight metabolic control of blood glucose are indispensable strategies in full-scope management of diabetic retinopathy. A number of eyes, however, will progress toward candidacy for surgical treatment despite aggressive implementation of these valuable interventions. According to the Early Treatment Diabetic Retinopathy Study, 5.3% of eyes receiving optimal medical treatment will still have progressive retinopathy that requires laser treatment and pars plana vitrectomy (PPV) (1).

Several complications of advanced diabetic retinopathy can be treated surgically. Vitrectomy can clear media opacities, relieve traction on the retina, make adequate laser treatment of the retina possible, and stabilize the proliferation process. Removal of premacular vitreous may also improve diabetic macular edema (DME).

Machemer and colleagues developed the PPV technique in 1971. The objective for Machemer vitrectomy was treating nonclearing vitreous hemorrhage from proliferative diabetic retinopathy. There have been many changes in the indications and in the timing for vitrectomy in diabetic retinopathy. New instrumentation, better understanding of the pathophysiology of the disease, development of surgical skills, and supplementary pharmacotherapy have improved surgical results (2–5).

The Diabetic Retinopathy Vitrectomy Study (6–8) was designed to evaluate the risks and benefits of performing early PPV in eyes with advanced proliferative diabetic retinopathy. The results from this study provide a better-defined role and timing of vitrectomy surgery for these conditions. The results of the study were obtained before the development of endolaser photocoagulation. Endophotocoagulation may be considered one of the most important reasons for performing a vitrectomy (9–12).

This book chapter will review the indications, techniques, results and complications of performing PPV for diabetic retinopathy.

INDICATIONS

Vitreous hemorrhage, traction retinal detachment involving the macula, and combined traction/rhegmatogenous retinal detachment are the classic indications (13, 14). The major indications for vitrectomy in diabetic retinopathy are summarized in Table 22-1. In 1987, Aaberg et al. (14) published a review that found that 15% of cases were performed exclusively for vitreous hemorrhage, 40% for traction macular detachment, and 35% for combined traction/rhegmatogenous retinal detachment. The remaining indications were severe fibrovascular proliferation, dense preretinal (premacular) hemorrhage, and other less common conditions (massive postvitrectomy fibrin response, progressive fibrolental proliferation). DME associated or not with posterior hyaloidal traction has been recognized as an indication for vitrectomy (15–17). Vitreopapillary traction may be an additional indication for vitrectomy (18).

TABLE 22-1 INDICATIONS FOR VITRECTOMY

Media opacities

A. Nonclearing hemorrhage

  1. Vitreous

  2. Subhyaloid, premacular hemorrhage

  3. Anterior segment neovascularization with posterior segment opacity

B. Cataract preventing treatment of severe proliferative diabetic retinopathy (lensectomy)

Traction defects

A. Progressive fibrovascular proliferation

B. Traction retinal detachment involving the macula

C. Combined traction and rhegmatogenous retinal detachment

D. Macular edema associated with taut, persistently attached posterior hyaloids

E. Vitreopapillary traction

Other indications

A. Ghost cell glaucoma

B. Anterior hyaloidal fibrovascular proliferation

C. Fibrinoid syndrome

D. Epiretinal membrane (nonvascularized)

VITREOUS HEMORRHAGE

Historically, the first indication for PPV was severe diabetic vitreous hemorrhage. As a result of the development of new techniques, the distribution of cases undergoing vitrectomy for vitreous hemorrhage decreased from about 70% in 1977 to about 20% in 1987 (14). Despite the extensive use of the panretinal photocoagulation, severe vitreous hemorrhages remain a very common reason for vitreous surgery. The surgical objectives include removal of vitreous hemorrhage to provide a clear medium, excision of the posterior hyaloid and epiretinal fibrovascular membranes to relieve vitreoretinal traction, and endolaser photocoagulation to achieve regression of proliferative tissue. The Diabetic Retinopathy Vitrectomy Study (7) demonstrated that diabetic type 1 patients had a more favorable visual outcome if the vitrectomy was performed in the first 6 months than with deferral for 1 year. For type 2 diabetic patients, the study did not show a significant difference in the 2 groups.

In general the recommended timing of vitrectomy for severe vitreous hemorrhage is before 3 months for type 1 patients and before 6 months for type 2 patients (19). Since type 2 diabetics more commonly have spontaneous resolution of hemorrhage and slower progression of fibrovascular proliferation, the usual approach for patients with type 2 diabetes is to defer surgical intervention longer than for patients with type 1 diabetes.

Several clinical features influence the recommended timing of vitrectomy for diabetic vitreous hemorrhage. Earlier surgical intervention is generally recommended when no previous laser treatment has been performed, when the fibrovascular proliferation complexes are more extensive and more vascular, when the fellow eye has rapidly progressive visual loss, or when the fellow eye is blind.

TRACTION AND COMBINED RETINAL DETACHMENT

The tractional defects constitute the majority of patients undergoing vitrectomy for complications of diabetic retinopathy. The spectrum of tractional involvement includes macular heterotopia, traction retinal detachment, and rhegmatogenous retinal detachment with a retinal break caused by progressive traction.

The most common indication for vitrectomy in diabetic patients is a traction detachment involving the macula. The main goal with the vitrectomy in these eyes is to relieve vitreoretinal traction by excision of the posterior hyaloid and epiretinal fibrovascular membranes (14, 20–23). The prognosis is better in cases with a short duration of the detachment, limited extension of the detachment, the presence of previous photocoagulation, and the absence of vitreous hemorrhage or severe neovascularization (21, 23, 24).

It is hard to predict when an extramacular detachment is going to progress and involve the macula. Because peripheral or midperipheral traction retinal detachments progress to involve the macula in only about 15% of cases per year, (25) caution is advised in recommending vitrectomy. Studies have demonstrated that early vitrectomy may benefits patients with progressive traction detachment that threatens the macula. (26). Macular detachment for a period greater than 6 months precludes the return of useful vision, and surgery may not be indicated.

Combined traction and rhegmatogenous detachment is an indication of vitrectomy regardless of the macular status. Combined detachment cases account for 17% to 35% of the diabetic eyes undergoing vitrectomy (14, 27). Progressive fibrosis and traction may lead to a retinal break resulting in a combined detachment. The break is usually small, posterior to the equator, and adjacent to the fibrovascular proliferation. Combined retinal detachment in proliferative diabetic retinopathy may occur in the setting of active fibrovascular proliferation or as a late complication. It is frequently associated with tightly adherent preretinal tissue and extensive detachment. Preoperative visual acuity best predicts visual prognosis (28).

SEVERE FIBROVASCULAR PROLIFERATION

Vitrectomy is indicated for patients with an attached hyaloid with active neovascular and fibrovascular proliferation despite extensive photocoagulation. If the vitreous and hyaloid is not removed, the fibrovascular tissue can undergo contraction, resulting in vitreous hemorrhage and retinal detachment. The vitrectomy study demonstrated more favorable visual and anatomic outcome with early vitrectomy than with conventional management (29, 30).

DIABETIC MACULAR EDEMA

DME accounts for 72% of blind patients with diabetes mellitus (31). Of the diabetic population, 9% develop macular edema, and 40% of these individuals have central macular involvement. (32). A small percentage of these patients have thickened posterior hyaloid associated with macular traction and diffuse macular edema. The patients with macular traction and diffuse macular edema have usually failed to respond to one or more prior macular photocoagulation sessions, and visual acuity is moderately reduced.

The vitreous is may contribute to the pathogenesis of DME. In the presence of vitreomacular separation, the macula edema is more likely to resolve (33). Lewis et al. (34) were first to describe a positive effect of PPV on diabetic patients who had a thickened posterior hyaloid membrane with traction on the macula. Tangential vitreomacular tractional forces combined with the local presence of a number of cytokines and growth factors (35) are thought to contribute to the development of DME.

From the pathophysiological point of view, vitrectomy could relieve the retina from the traction forces. Optical coherence tomography (OCT) facilitates the visualization of the vitreoretinal interface and the identification of eyes with diffuse macula edema that should benefit from surgery. Vitrectomy may also improve the oxygen and nutrients supply from the vitreous cavity to the macula. The condensed posterior premacular hyaloid may prevent diffusion caused by the accumulation of cytokines (produced by the ischemic retina) which may lead to a diffuse breakdown of the inner blood-retinal barrier, thus generating diffuse edema. After vitrectomy, these cytokines may escape easier into the vitreous cavity.

Several studies have reported favorable outcomes of PPV for diabetic eyes with or without visible taut and thickened posterior hyaloid (36, 37). The surgical goals in these cases include opening, elevating, and removing the posterior hyaloid with or without peeling of the internal limiting membrane (ILM).

Combinations of the mechanical surgical approach with pharmacological adjuncts (intravitreal bevacizumab or intravitreal triamcinolone) may further improve success rates for the treatment of diffuse DME.

OTHER INDICATIONS: PREMACULAR HEMORRHAGE

This is characterized by blood that is tightly confined between the macula and the posterior vitreous face of an incomplete vitreous detachment without a fully separated posterior hyaloid. 6% to 10% of vitrectomies are performed for this indication (38, 39).

Usually, the hemorrhage is oval and obscures the fundus detail. Some of these hemorrhages clear spontaneously; in spite of that, surgical intervention should be considered relatively early in course to prompt recovery of visual acuity and to prevent severe macular traction or wrinkling of the fovea. The presence of hemorrhage in contact with the hyaloid face and ILM stimulates the growth of fibrous tissue. The fibrovascular tissue may contract and result in macular traction detachment.

OTHER INDICATIONS: ANTERIOR SEGMENT NEOVASCULARIZATION

When iris or angle neovascularization is present in eyes with vitreous hemorrhage, panretinal photocoagulation cannot be performed; so, vitrectomy surgery with endolaser photocoagulation is indicated. The goal of the vitrectomy in these cases is preventing the neovascular glaucoma (40, 41).

In eyes with established neovascular glaucoma, vitrectomy surgery in conjunction with a glaucoma procedure (tube implantation) is sometimes indicated (42, 43).

OTHER INDICATIONS: GHOST-CELL/HEMOLYTIC GLAUCOMA

After vitreous hemorrhage, glaucoma can develop. The reason for elevation of intraocular pressure (IOP) may result from impedance of outflow in the trabecular meshwork. Erythroclastic cells (ghost cells) are large in size and cannot pass through the trabecular meshwork. Blood-induced open-angle glaucoma may also result from erythrocytic debris and/or macrophages containing erythrocytic debris (hemolytic cells). The indication for vitrectomy surgery is uncontrolled IOP despite maximal medical therapy (44, 45).

SURGICAL TECHNIQUE

The surgical objectives of vitrectomy are to address the complications of proliferative diabetic retinopathy that result in visual loss. The goals of vitrectomy are to remove axial opacities, relieve anterior-posterior and tangential traction, control hemostasis, deliver laser treatment, and treat retinal breaks.

A variety of equipment and instruments may be used to achieve these objectives. Instruments like intraocular infusion fluids, contact lenses and wide-angle viewing systems, vitreous cutting instruments, ultrasonic phacofragmentation devices, fiberoptic illuminators, diathermy instruments, photocoagulation devices, cryoprobes, as well as a variety of intraocular blades, cannulas, scissors, forceps, and picks. Long-acting gases and silicone oil are additional agents that remain in the eye for an extended period of time. The typical vitreous cutter is 20-gauge; however, 23-gauge and 25-gauge instruments are available.

VITRECTOMY AND MEMBRANECTOMY FOR VITREORETINAL TRACTION

The degree of posterior vitreous separation and pathoanatomy determine the approach to vitrectomy. In most cases, the selected surgical approach is customized as a hybrid of all techniques.

Complete Posterior Vitreous Detachment

The usual indication for surgery in this case is nonclearing ­vitreous hemorrhage. A core vitrectomy is performed to remove the central vitreous. After one opening is created in the hyaloid, it should be enlarged circumferentially; hemorrhage over the ^­

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