Primary Vitrectomy in Rhegmatogenous Retinal Detachment

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Chapter 102 Primary Vitrectomy in Rhegmatogenous Retinal Detachment

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Introduction

Currently, rhegmatogenous retinal detachment (RRD) continues to be an important cause of visual loss. The fundamental principles involved in reattachment of a retina include identification of all retinal breaks, and relief of the vitreous traction. Traditionally, scleral buckling (SB) was viewed as the gold standard treatment for uncomplicated RRD. Pars plana vitrectomy (PPV) was traditionally reserved for treatment of eyes with complications, such as those showing giant retinal tears or exhibiting significant proliferative vitreoretinopathy (PVR). In the 1980s, the indications for PPV in RRD patients were broadened to include less complicated instances, and the term “primary vitrectomy” was introduced by Klöti.1

As the necessary instrumentation for, and safety of, PPV continue to improve with developments in microscope technology, intensified endoillumination, and wide-angle viewing systems, the indications for vitrectomy in RRD have been further expanded to include most patients with RRD. Indeed, PPV is more useful than SB in eyes requiring simultaneous cataract extraction or those of pseudophakic status.28

Compared to SB, PPV offers several advantages. The view of the retinal periphery is enhanced, identification of retinal breaks is rendered easier, achievement of complete intraoperative retinal attachment is possible, the risks of hemorrhage or retinal incarceration inherent to the external drainage procedure applied during SB is eliminated, and the technique is less likely to cause a refractive change. In addition, the recent introduction of small-gauge vitrectomy has shifted the paradigm of standard vitreous surgery to microincision vitrectomy surgery that is less invasive, affords fast recovery, and is sutureless (the acronym for such surgery is MIVS). As a result of these advances, vitreoretinal surgeons now have more procedural choices when treating RRD patients. Further, recently trained vitreoretinal surgeons may be more familiar with application of PPV (compared to SB) in challenging situations.

In this chapter, the use of primary vitrectomy for treatment of RRD, and the advantages and disadvantages of employing different gauges of vitrectomy system will be explained and evaluated.

Pathogenesis of Rhegmatogenous Retinal Detachment

The vitreous is firmly attached to the vitreous base, an area 3–6 mm in diameter that straddles the ora serrata surrounding the retina. The posterior border of the vitreous base is located both more posteriorly and temporally in older individuals. Therefore, retinal tears may occur at a higher frequency at the temporal periphery in such patients, following posterior vitreous detachment (PVD).

Three factors predispose to development of RRD: (1) the existence of a liquefied vitreous gel; (2) tractional forces that precipitate a retinal break; and (3) the presence of a retinal break through which fluid may access the subretinal space.

Liquefaction of the vitreous occurs naturally upon aging, developing more rapidly in eyes with significant myopia, surgical or non-surgical trauma, and/or intraocular inflammation. Apart from liquefaction, alterations in the extracellular matrix of the vitreous facilitate detachment of the posterior vitreous from the underlying retina. PVD usually presents as an acute event, and is more prevalent in patients older than 50 years, with frequencies as high as 53%.9 PVD often precipitates RRD because the tractional forces necessary to generate retinal breaks are produced upon development of PVD, although not all retinal breaks progress to detachment. The reported incidence of retinal tears in patients with acute symptomatic PVD varies from 8–46%.10 In a study in a general population,11 18% of eyes with retinal breaks developed retinal detachment. Risk factors for progression included fresh, symptomatic, horseshoe-shaped tears; breaks suggestive of the presence of subclinical retinal detachment (RD); and pseudophakia/aphakia.

Categories of Rhegmatogenous Retinal Detachment

No internationally accepted RRD classification has been established. The various reports suggest that the type of break, the status of the vitreous, and the need for cataract surgery are all important when defining the categories of RRD.

Retinal breaks are traditionally classified as round holes, tears, or resulting from retinal dialysis. Accordingly, RRD can be categorized as: (1) round hole retinal detachment; (2) retinal detachment occurring secondary to retinal tears; and (3) retinal detachment attributable to retinal dialysis. This categorization, and the status of the vitreous, are important when exploring management options, in particular whether SB or vitrectomy should be employed.

Retinal holes are full-thickness retinal defects that usually occur as a result of localized atrophic intraretinal abnormalities or lattice degeneration, and are not associated with vitreoretinal traction. Typical RD patients with round holes show one or more areas of limited retinal detachment, and may thus be optimally treated with either laser demarcation or segmental SB, rather than vitrectomy.

Retinal tears are usually produced by PVD and subsequent vitreoretinal traction. As persistent vitreous traction at an edge usually causes detachment to progress, the vast majority of RD patients in this category require surgical treatment. Among the various methods available, release of traction via PPV is preferred by many vitreoretinal surgeons.

Retinal dialysis is most often associated with blunt ocular trauma, and rarely occurs spontaneously. Dialyses are most common in the inferotemporal quadrant. The vitreous remains firmly attached to the entire peripheral retina, and vitreoretinal traction caused by gravity results in slow retinal detachment. Vitrectomy in an eye with an attached vitreous gel can be technically difficult, and may introduce unnecessary surgical complexity. Therefore, vitrectomy is less desirable than are other treatment options.

The number of aphakic/pseudophakic patients with RRD has increased significantly over the past decades. After cataract surgery, vitreous liquefaction accelerates, causing premature PVD and subsequent RD. Aphakic/pseudophakic eyes tend to have small (and sometimes multiple) anterior breaks. The status of the posterior capsule also influences the speed of vitreous liquefaction. One study found that Nd:YAG laser posterior capsulotomy increased the risk of RD after cataract extraction up to 4.9-fold.12 Because of the characteristics of the breaks and the status of the vitreous in aphakic/pseudophakic eyes, vitrectomy is preferred by many surgeons and has a good success rate.13

Patient selection for primary vitrectomy

SB and/or pneumatic retinopexy serve as the first treatment option(s) in patients with localized detachment in one quadrant together with single neighboring breaks. Young age and anteriorly located small holes in phakic patients encourage the use of SB. The success rates of final reattachment are 90–95%.14

PPV is indicated for patients with wide and bullous RD, and for older patients with a liquefied vitreous. The presence of RD with marked traction with different anterior posterior depth of breaks, the presence of breaks in multiple quadrants, or the absence of an apparent retinal break in a pseudophakic patient, are all good candidates for the use of PPV. RD of preoperative PVR grade C, giant tear-induced RD, and macular hole RD, are all commonly treated using PPV.

Recent developments in vitrectomy instruments, including small-gauge systems, wide-angle viewing systems, and endoilluminators, as well as adjuvants, including triamcinolone acetonide suspension, perfluorocarbon liquids, and intraocular tamponades, led the choice of surgical technique for the treatment of RRD with medium-complexity shift more and more towards PPV.1517 During the last 5 years, several surgeons have reported that primary vitrectomy is the method of choice in 40–80% of all patients with RRD.17,18

Several trials comparing PPV to SB in patients undergoing RRD surgery have been reported.1923 In general, PPV was favored for treatment of pseudophakic eyes with unseen breaks, eyes featuring ocular hypotony, or eyes showing prolonged macular detachment. One large-scale prospective multicenter randomized trial, scleral buckling versus primary vitrectomy in rhegmatogenous retinal detachment study (the SPR Study), also supported the superiority of PPV in the pseudophakic/aphakic eyes, in terms of a primary success rate and a rate of retina-affecting secondary procedures. This study, however, showed no differences in phakic eyes.19

The results to date suggest that SB or PPV is a good treatment option for primary phakic RRD, whereas PPV may be preferable to SB when pseudophakic RRD is to be treated. It is important to consider individual patient factors, surgeon preference, and availability of equipment, to make an optimal treatment decision.

Principles of vitrectomy

The principles of vitrectomy to treat RRD are release of tractional forces that precipitated the retinal break, and the closure and reattachment of breaks to the underlying retinal pigment epithelium. The surgical procedure requires: (1) removal of the vitreous gel and preretinal tractional membrane; (2) intraoperative flattening of the detached retina; (3) application of retinopexy; and (4) placement of a tamponade in the vitreous cavity.

Abnormal vitreoretinal traction (either perpendicular or tangential) increases vitreous mobility caused by PVD, and atypical posterior extension of the anterior vitreous base predisposes to formation of retinal tears. Therefore, removal of the vitreous gel and any abnormal preretinal structure releases the tractional force causing retinal breaks and detachment.

After release of abnormal vitreoretinal traction, the detached retina must be reattached. To stabilize and flatten the detached retina, a heavy liquid is initially applied; this is subsequently replaced by sterile air. If the retina is mobile and becomes flattened in air, a nonexpansive gas–air mixture is used to achieve a postoperative gas tamponade. Although silicone oil is not routinely used in instances of uncomplicated RRD, use of silicone oil should be considered if eyes have multiple inferior breaks, if PVR is present, or if the eye is an only seeing eye. Retinopexy has been used to create permanent retinal–RPE adherence. Both forms of retinopexy (cryopexy, and the laser photocoagulation) cause tissue destruction and cellular proliferation and should be used as little as possible. Continuous laser retinopexy is preferable to cryopexy, because cryopexy probably causes more tissue damage and a greater proliferative reaction than laser retinopexy. However, if peripheral breaks in phakic eyes are to be treated, cryopexy is preferred, because the endolaser probe can touch the crystalline lens. The risk of postoperative PVR may be minimized if retinal pigment epithelial cells dispersed after cryopexy are thoroughly aspirated via a heavy liquid–air exchange.

Surgical techniques

Primary vitrectomy is commonly performed using a wide-angle viewing system attached to an operating microscope. The surgical steps of primary vitrectomy using sutureless MIVS are described below (Figs 102.1102.4).

Core vitrectomy

First, the central vitreous is removed (Fig. 102.1). When PVD is absent, or even when PVD has occurred, triamcinolone acetonide can be injected to afford better visualization of the vitreous gel, to facilitate PVD, and to completely remove the residual vitreous. The posterior vitreous membrane can be removed using a diamond-dusted scraper; this prevents secondary macular pucker (Fig. 102.5).