700 mg implant, 31% had ten or more letters improvement at 90 days compared to 15% of 34 patients in the control group, a result similar to the overall study result for all eyes that reached signiÞcance with P < 0.001.155 As with other forms of intravitreal steroid treatment, anatomic success does not equate with functional success in many cases, perhaps due to chronicity of the edema and cell death.85,253

Because of the lack of sustained effect, the high frequency of intraocular pressure elevation, the secondary cataract formation in phakic patients, and the efÞcacy of anti-VEGF therapy without the side effects, intravitreal steroid treatment for CRVO with ME has not been adopted widely.128 It is useful as a secondary therapy in patients refractory to anti-VEGF treatment and in pseudophakic patients whose IOP does not rise in response to steroids. In the latter group, it has the advantage of longer duration of action compared to anti-VEGF treatment and may be chosen as Þrst-line treatment in some instances. A head- to-head clinical trial of anti-VEGF and intraocular steroid treatment would be helpful to deÞne the relative effectiveness of these two treatments that are both superior to observation.

13.4.2.6 Vitrectomy

Pars plana vitrectomy with various adjunctive maneuvers including ILMP, PRP, and intravitreal or subretinal injection of various drugs has been tried as treatment for CRVO with ME.

In an uncontrolled case series of 14 eyes, preoperative mean VA improved from Snellen decimal VA of 0.17Ð0.31 at 12 months after surgery.271 Better preoperative VA and earlier intervention have been correlated with better Þnal VA. In four uncontrolled series, the consistent Þnding was that macular thickness could be decreased with this surgery, but that VA did not improve as consistently. Timing of intervention was suggested to be important with earlier intervention associated with more favorable visual results than later intervention. In one series, the effectiveness did not depend on perfusion status of the retina.177

Vitrectomy for macular edema associated with CRVO signiÞcantly improves vision-related quality of life.204 Three months after surgery, the composite score on the VFQ-25 improved from a preoperative mean of 60.4±17.6 to 66.4±11.0 (P <0.05).204

13.5Treatment of Intraocular Neovascularization

13.5.1Sector Panretinal Laser Photocoagulation for Retinal and Disc Neovascularization After Branch Retinal Vein Occlusion

The natural history of major BRVO is that 19Ð22% will develop NVE or NVD, of which 61Ð90% will suffer vitreous hemorrhage (VH) (see Chap. 10).92,106 Case series and later two randomized clinical trials have demonstrated the efÞcacy of sector PRP for reducing VH associated with retinal neovascularization after major BRVO.24,81,92 With sector PRP, the percentage developing NVE or NVD and going on to VH can be reduced to 30%.24

Treatment can be given with or without retrobulbar anesthesia. In the BVOS, 74% of treatments were accomplished with topical anesthesia alone, and 26% required the addition of retrobulbar anesthesia.24 Techniques to reduce pain during PRP include shortening the duration of the pulses and using micropulse laser photocoagulation.5,234 Laser spot size is typically 200Ð500 m with a burn separation of one burn width between adjacent burns, is given no closer than two disc diameters from the center of the macula, and covers the area of retinal hemorrhage and capillary nonperfusion in the involved sector of the retina.

The intensity of laser burns has decreased over the years. In the BVOS, the burn intensity was prescribed as medium-white. Now panretinal laser burns are prescribed to be gray-white (lighter).

Experimental models of BRVO show that preretinal PO2 values are higher over photocoagulated

than nonphotocoagulated regions of the retina. Thus, the hypothesis that laser photocoagulation improves the diffusion of oxygen from the choroid to the inner retina appears to be correct.224,268

It is important to photocoagulate the entire area of ischemic retina.224 In some cases, guidance with FA can be helpful in assessing the extent of ischemic retina, although this test is not routinely needed.

The BVOS suggested that sector PRP be given only upon development of NVD or NVE, not prophylactically for the presence of capillary nonperfusion alone. However, the study authors admitted that the study was not designed to answer the question when sector PRP should be given.24 A separate prospective study reached the same conclusions as the BVOS.106 One reason for waiting until neovascularization develops is that many BRVOs are in the superior quadrants and superior sectoral PRP can worsen the important inferior visual Þeld.231 Other retrospective studies have disagreed with the recommendations of the BVOS and instead advocated sector PRP upon the presence of capillary nonperfusion without retinal or disc neovascularization, the rationale being the observed reduction in incidence of neovascularization when this course was followed. The recommendation of the BVOS was made because it provided suggestive evidence that there is time to do sector PRP once neovascularization appears without incurring a higher incidence of vitreous hemorrhage or an adverse visual outcome. A calculation was made that 12% of nonperfused eyes treated before the onset of neovascularization would develop vitreous hemorrhage anyway, compared to 9% if eyes were not treated until neovascularization developed.24 Moreover, the more conservative approach of withholding sector PRP until the development of neovascularization prevents unnecessary treatment of the proportion of eyes with capillary nonperfusion that do not progress to retinal or disc neovascularization.24 The BVOS approach assumes that eyes are followed up at 4-month intervals until the risk of neovascularization is judged to be minimal, an interval never explicitly stated. Based on the authorÕs clinical experience, this interval is probably on the order of 1 year.

Atrophy of preretinal neovascularization after sector PRP is usually evident within 2 months after treatment. Re-treatments may be needed especially in cases partially obscured by overlying vitreous hemorrhage.92

13.5.2Vitrectomy for Intraocular Neovascularization with Vitreous Hemorrhage

As with all cases of nonclearing vitreous hemorrhage, those associated with BRVO and secondary retinal or optic disc neovascularization are uncontroversially addressed by vitrectomy.253 A case series of 113 eyes undergoing vitrectomy for complications of BRVO found that need for reoperation was more frequent in cases with partial rather than complete posterior vitreous detachment.275

Vitrectomy is commonly used to manage patients with traction retinal detachment associated with RVO. The techniques are standard with no RVO-speciÞc maneuvers relative to this particular indication.242

13.5.3Laser Panretinal Photocoagulation for Anterior Segment Neovascularization

Panretinal photocoagulation was shown to be effective in causing regression of anterior segment neovascularization following CRVO in the 1970s.156,182,321 Both argon laser and xenon arc PRP were found to be effective in reducing the frequency of progression of eyes with ischemic CRVO to neovascular glaucoma.156,157,182,321 Xenon arc PRP was abandoned because of the high rate of complications including choroidal detachment, iris burns, and secondary preretinal Þbrosis.182 VA was not improved by treatment.156,157,182,321 Later studies showed that PRP works by reducing intraocular levels of VEGF.23,157,279 In some instances, more than one session of laser is necessary to cause the new vessels to regress.