Ординатура / Офтальмология / Английские материалы / Diabetes and Ocular Disease Past, Present, and Future Therapies 2nd edition_Scott, Flynn, Smiddy_2009

214 Diabetes and Ocular Disease

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Figure 11.5. (A) Fibrovascular proliferation typically progresses from neovascularization of the nerve head and along the arcade with, initially, relatively good visual acuity. This 29-year-old woman presented with vision of 20/30. (B) With further progression over the ensuing three months, the visual acuity dropped to 20/200 as the fibrovascular proliferation enveloped the posterior pole. (C) After vitrectomy, the vision returned to 20/30.

and patients with severe retinopathy in the fellow eye should be considered for earlier vitrectomy. Chronic macular detachment leads to thinner, more atrophic retina, with more extensive and more tightly adherent fibrovascular membranes. Consequently, the anatomic and visual prognoses are poorer in such patients; macular detachment for 6 months or more has a poor visual prognosis and may not be recommended for surgery [19,25].

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Figure 11.6. (Continued)

profound visual loss usually occurs soon after the rhegmatogenous component occurs. While some cases with a rhegmatogenous component may be only slowly progressive and could be monitored closely without surgery, more commonly, prompt surgery is indicated. The pathogenic retinal break typically occurs posterior to the equator, but may be obscured by FVP and not be appreciable during the preoperative examination. Common sites for retinal breaks include areas adjacent to previous chorioretinal scars or at the base of vitreoretinal adhesions.

A more subtle traction-induced complication is macular edema induced by the traction of a taut, persistently attached posterior hyaloid. While this is uncommon, it is demonstrated readily on OCT. This subtype of diabetic macular edema characteristically does not respond to focal laser photocoagulation or intravitreal corticosteroids. The vast majority of diabetic macular edema cases are not induced by traction and should be considered for photocoagulation in accordance with the results of the Early Treatment Diabetic Retinopathy Study [48] or, in selected cases, for intravitreal corticosteroids. Selected cases with this configuration respond to surgical release of the traction [24,29]. A subsequent study corroborated those results but also emphasized both the rarity of the condition and the difficulty in accurately assessing such cases during the preoperative examination [30]. Other techniques that involve internal limiting membrane removal in cases with even less apparent traction are still being evaluated.

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Figure 11.7. (A) With continued traction, especially with more broad-based fibrovascular entities, a rhegmatogenous component may develop in the retina. This leads to a more generalized retinal detachment, which may be apparent as rapid onset of decreased vision, extensive retinal detachment, and hydration lines. (B) Postoperative appearance of this patient. Visual acuity remained 20/400.

Complications of Previous Vitrectomy. A third, miscellaneous category of vitrectomy indications includes complications from a previous vitrectomy. As in primary cases, there are two broad subcategories: media opacities and traction. Severe recurrent vitreous hemorrhage not only constitutes a media opacity but may also induce a secondary glaucoma through a ghost cell mechanism [49–52]. Most such cases are self-limited (spontaneous clearing of hemorrhage) or respond to medical therapy (glaucoma), but selected cases will respond to vitrectomy by debulking the substrate for outflow blockage [53]. In some cases, office-based fluid–gas exchange may provide sufficient elimination of blood, avoiding repeat vitrectomy in the operating room [54,55]. In most cases, however, recurrent severe vitreous hemorrhage after vitrectomy is a manifestation of reproliferation, retinal break formation, or other more severe complications that require operative repair.

Retinal detachment—either tractional or rhegmatogenous—after previous vitrectomy may constitute an indication for repeat vitrectomy. Such cases usually have a guarded visual prognosis because of coexisting proliferative vitreoretinopathy (PVR). Silicone oil may be considered for retinal tamponade.

An especially difficult condition to control is progressive anterior hyaloid FVP that typically occurs several weeks following vitrectomy. These cases are usually

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managed by lensectomy and extensive anterior vitreous dissection similar to techniques used for PVR [56].

Intravitreal injection of bevacizumab may be useful preoperatively in eyes with extensive FVP in order to reduce intraoperative bleeding [57,58]. Although no randomized prospective study has been conducted, the use of preoperative bevacizumab has gained considerable popularity. However, progressive traction retinal detachment following intravitreal bevacizumab has being described in patients with severe proliferative diabetic retinopathy and these cases may have very poor visual outcomes [59].

A rare entity after vitrectomy is the fibrinoid syndrome, which involves extensive fibrinous membrane cross-linking of the vitreous [60]. The fibrinoid syndrome may reflect ischemia and increased vascular permeability. Minor degrees of postoperative fibrin formation usually resolve spontaneously, but when severe degrees of fibrin occur, as is characteristic of fibrinoid syndrome cases, tissue plasminogen activator [61] or streptokinase [62] may be useful. The visual prognosis is guarded, but pretreatment with intravitreal triamcinolone acetonide has been suggested to attempt to reduce the severity of this complication. Similarly, intraoperative use of intravitreal triamcinolone may reduce this complication.

SURGICAL OBJECTIVES AND TECHNIQUES

The surgical objectives of vitrectomy for complications of diabetic retinopathy are to neutralize and, when possible, to eliminate the components that have led to the visual loss (Table 11.2). These objectives are usually interrelated and involve removal of axial media opacities, relief of preretinal traction, and delivery of appropriate laser treatment. New instruments and techniques have emerged in response to the need to achieve these objectives more safely and reproducibly.

Media Opacities. Endoillumination, an operating microscope, and an optical viewing system provide standard visualization of the vitreous strands and surfaces.

Removal of axial opacities involves the vitreous cutter, the extrusion needle, and lensectomy instruments. Newer instruments now offer better control of cutting rates, suction pressure, and fragmentation power and mode. Removal of vitreous

Table 11.2. Objectives of Vitrectomy for Severe Diabetic Retinopathy

1.Remove axial opacities

2.Relieve anteroposterior traction

3.Relieve tangential traction

4.Segment or peel epiretinal membranes

5.Effect hemostasis

6.Treat all retinal breaks

7.Deliver laser treatment

a.Limited or full panretinal photocoagulation

b.Local treatment of flat neovascularization elsewhere

8.Use retinal tamponade if necessary

a.Air or gas

b.Silicone oil

and FVP is facilitated with more complete posterior vitreous separation. In eyes not requiring extensive membrane dissection, 23or 25-gauge transconjunctival vitrectomy is a useful option for clearing media opacities and applying endolaser PRP. Improving ancillary instrumentation has allowed the application of 23or 25-gauge surgery to increasingly complex vitreoretinal traction in diabetic retinopathy.

Vitreoretinal Traction. Elimination of traction involves removal of anteroposterior and tangential vitreoretinal traction, as well as removal of membrane-induced surface traction. At least three conceptually different surgical techniques have been developed to achieve these goals [63–71]. While each technique seems to represent a different approach, all achieve the same objectives albeit in a different sequence:

1.Segmentation: the traction is sequentially dissected by removing anterior to posterior traction (Fig. 11.8A), scissors dissection of bridging epiretinal traction (Fig. 11.8B) and, finally, removal of residual islands of surface traction including epiretinal membranes [63,64] (Fig. 11.8C).

2.Delamination: the anteroposterior traction is commonly removed first. Preretinal tissue is removed using horizontal scissors and multifunction instruments (such as lighted picks or lighted forceps) at the retinal plane as one or more large pieces [65,66] (Fig. 11.9). In this regard, it is similar to the “en bloc” technique except that the anterior to posterior traction of the vitreous has been removed previously. Delamination techniques are reported to induce less intraoperative bleeding than segmentation techniques.

3.“En bloc”: the surface traction is removed with scissors as a large, confluent piece using the anteroposterior traction for countertraction before relief of anteroposterior traction [68–72] (Fig. 11.10). The theoretical advantage of this technique is that the anteroposterior traction serves as a “third hand” function by retracting tissue from the retinal surface so that subsequent surface dissection is facilitated. The anteroposterior traction and the bulk of the vitreous are removed as the last step. Initial reports suggested that this technique was associated with more intraoperative retinal breaks (35% in an early report) [70], but further experience yields a rate equivalent to other techniques (20%) [71]. The consequences of an iatrogenic retinal break (as long as it is appropriately treated) when the traction has been relieved more fully are minimal compared to leaving traction unrelieved. In many cases, the selected surgical technique is a hybrid of all three techniques. Use of high-speed vitrectomy probes (e.g., 2500 cuts per minute) and 23or 25-gauge surgery may reduce the need for scissors or other ancillary instrumentation [72,73].

Scleral buckling may be necessary to neutralize peripheral retinal traction from unreachable or undissectable membranes [74], especially in cases with combined tractional and rhegmatogenous retinal detachment.

Control of Hemorrhage and Reproliferation. Intraoperative hemostasis facilitates completion of the other surgical objectives and optimizes the chance for surgical success by reducing postoperative fibrin and blood. While the latter are most apparent as media opacities, a potentially more deleterious factor is that they may contain promoters of cellular proliferation or serve as a template for reproliferation.

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Figure 11.8. This series of illustrations demonstrates the technique of vitreoretinal surgery in which first media opacities and anterior to posterior traction is relieved (A), followed by relief of bridging traction (B), typically with the vitreous cutter (C). Vitreoretinal picks and scissors are used to segment preretinal membrane components. The final result is one of removal of all posterior segment traction with remnant stumps of fibrovascular proliferation. Sometimes, the fibrovascular proliferation is extensive and the posterior hyaloid is well defined. In such cases, the hyaloid may be peeled up in a relatively confluent fashion and fewer fibrovascular stumps ensue. This is more similar to the delamination technique. (Source: Redrawn with permission of Johns Hopkins University from Michels RG: Proliferative diabetic retinopathy: pathophysiology of extraretinal complications and principles of vitreous surgery. Retina 1981;1:1–17.)

Strategies to control bleeding include using intravitreal diathermy, increasing the infusion pressure, or using intraocular thrombin [75,76]. Optimal intraoperative control of systemic blood pressure lessens intraoperative and postoperative bleeding. Preoperative treatment with an anti-VEGF agent such as bevacizumab has been reported to reduce intraoperative bleeding [77–79]; the scope of its recommended use is being widely investigated.

An important surgical objective is control of reproliferation. With the advent of improved endolaser [80–84] and indirect laser ophthalmoscopic delivery systems

Figure 11.12. Noncontact wide-field viewing system for pars plana vitrectomy using 25-gauge instruments.

probes combined the functions of infusion, suction, and cutting. Later generations of instruments separated these three essential tasks and allowed smaller sclerotomies, which may have lowered the risk of iatrogenic retinal dialysis. The light probe has been modified to allow additional functions, including the illuminated pick or forceps or illuminated endolaser probe, while preserving a normal-sized sclerotomy. A multiport illumination system freeing up the second hand to use a pick or forceps has also been developed. The transconjunctival 23or 25-gauge instrumentation system (Fig. 11.11) can achieve the surgical objectives and the small incisions may decrease morbidity and speed up postoperative recovery [72,73].

Wide-field viewing systems (Fig. 11.12) have been developed and are now commonly used to facilitate the global view of the posterior segment, thereby lessening the risk of inducing unintended traction and retinal breaks in distant areas [99,100]. Another useful innovation has been iris retractors [100–102]. Usually reserved for pseudophakic or aphakic patients, iris retractors facilitate achieving surgical objectives by allowing a maximum view of the posterior segment in patients with fi xed, small pupils.

OUTCOMES OF VITRECTOMY

Concomitant traction, capillary nonperfusion, retinal detachment and macular edema influence visual acuity outcomes in patients with diabetic retinopathy. Thus, very few cases present with vitreous hemorrhage as the sole cause of visual loss because concurrent diabetic maculopathy and extensive capillary nonperfusion frequently coexist. With improvements in instrumentation, the complications of vitrectomy have decreased, allowing surgical intervention in patients with better preoperative visual acuity.

Media Opacities. The results of vitrectomy for nonclearing diabetic hemorrhage have been reviewed extensively [19,20,32–34,37,103,104]. The vision improves in