Antagonism of Vascular Endothelial Growth Factor for Macular Edema Caused by Retinal Vein Occlusions: Two-Year Outcomes

Retinal vein occlusion and macular edema - critical evaluation of the clinical value of ranibizumab

Retinal vein occlusions (RVOs) constitute the second most common cause of retinal vascular disease after diabetic retinopathy, with a prevalence of between 1% and 2% in persons older than 40 years of age. Despite the existence of numerous potential therapeutic options, none is entirely satisfactory, and many patients with RVO suffer irreversible visual loss. Fortunately however, the recent introduction of antivascular endothelial growth factor (VEGF) agents, such as ranibizumab (Lucentis^®, Genentech, South San Francisco, CA) and bevacizumab (Avastin^®, Genentech), offers a potentially new treatment approach for clinicians managing this disorder. The results of the BRAVO and CRUISE trials have provided the first definitive evidence for the efficacy and safety of ranibizumab in the treatment of RVO. As a result, ranibizumab has recently been approved by the US Food and Drug Administration for the treatment of RVO-associated macular edema. In this review, we provide a critical evaluation of clinical trial data for the safety and efficacy of ranibizumab, and address unresolved issues in the management of this disorder.

Treatment of macular edema due to retinal vein occlusions

Retinal vein occlusion (RVO) is a prevalent retinal vascular disease, second only to diabetic retinopathy. Previously there was no treatment for central retinal vein occlusion (CRVO) and patients were simply observed for the development of severe complications, generally resulting in poor visual outcomes. The only treatment for branch vein occlusion (BRVO) was grid laser photocoagulation, which reduces edema very slowly and provides benefit in some, but not all patients. Within the past year, clinical trials have demonstrated the effects of three new pharmacologic treatments, ranibizumab, triamcinolone acetonide, and dexamethasone implants. The benefit/risk ratio is best for intraocular injections of ranibizumab, making this first-line therapy for most patients with CRVO or BRVO, while intraocular steroids are likely to play adjunctive roles. Standard care for patients with RVO has changed and will continue to evolve as results with other new agents are revealed.

Vascular stem cells and ischaemic retinopathies

Retinal ischaemic disorders such as diabetic retinopathy and retinal vein occlusion are common. The hypoxia-related stimuli from oxygen-deprived neural and glial networks can drive expression of growth factors and cytokines which induce leakage from the surviving vasculature and/or pre-retinal and papillary neovascularisation. If left untreated, retinal vascular stasis, hypoxia or ischaemia can lead to macular oedema or fibro-vascular scar formation which are associated with severe visual impairment, and even blindness. Current therapies for ischaemic retinopathies include laser photocoagulation, injection of corticosteroids or VEGF-antibodies and vitreoretinal surgery, however they carry significant side effects. As an alternative approach, we propose that if reparative intra-retinal angiogenesis can be harnessed at the appropriate stage, ischaemia could be contained or reversed. This review provides evidence that reperfusion of ischaemic retina and suppression of sight-threatening sequelae is possible in both experimental and clinical settings. In particular, there is emphasis on the clinical potential for endothelial progenitor cells (EPCs) to promote vascular repair and reversal of ischaemic injury in various tissues including retina. Gathering evidence from an extensive published literature, we outline the molecular and phenotypic nature of EPCs, how they are altered in disease and provide a rationale for harnessing the vascular reparative properties of various cell sub-types. When some of the remaining questions surrounding the clinical use of EPCs are addressed, they may provide an exciting new therapeutic option for treating ischaemic retinopathies.