Intravitreal Ranibizumab or Triamcinolone Acetonide in Combination With Laser Photocoagulation for Diabetic Macular Edema

Thus far the only demonstrated means to reduce the risk of vision loss from diabetic macular edema are laser photocoagulation, intensive glycemic control, and blood pressure control. Earlier studies have shown that photocoagulation, although effective in reducing the risk of moderate vision loss, can eventually result in retinal and retinal pigment epithelium atrophy resulting in loss of central vision, central scotomata, and decreased color vision. Consequently, many retinal specialists today tend to treat diabetic macular edema (DME) with lighter, less intense laser burns than was originally specified in the Early Treatment Diabetic Retinopathy Study (ETDRS). The additional unsatisfactory outcome from treatments with laser photocoagulation in a significant proportion of eyes with DME has prompted interest in other treatment modalities. One such treatment is pars plana vitrectomy. Studies suggest that vitreomacular traction may play a role in increased retinal vascular permeability, and that removal of the vitreous, or relief of mechanical traction with vitrectomy and membrane stripping may substantially improve macular edema and visual acuity. However, this treatment may be applicable only to a specific subset of eyes with a component of vitreomacular traction secondary to edema. Other treatment modalities such as pharmacologic therapy with oral protein kinase C inhibitors and intravitreal corticosteroids are under investigation.

The use of antibodies targeted at vascular endothelial growth factor (VEGF) is another treatment modality that needs to be further explored for its potential benefits. Increased VEGF levels have been demonstrated in the retina and vitreous of human eyes with diabetic retinopathy. VEGF, also knows as vascular permeability factor, has been shown to increase retinal vascular permeability in in vivo models. Therapy that inhibits VEGF, therefore, may represent a useful therapeutic modality which targets the underlying pathogenesis of diabetic macular edema. Ranibizumab is a promising anti-VEGF drug. Its efficacy and safety have been demonstrated in treatment of age-related macular degeneration. Reports of its use and that of other anti-VEGF drugs in DME have suggested sufficient benefit to warrant evaluation of efficacy and safety in a phase III trial. Corticosteroids, a class of substances with anti-inflammatory properties, have also been demonstrated to inhibit the expression of the VEGF gene. The Diabetic Retinopathy Clinical Research Network (DRCR.net) is currently conducting a phase III randomized clinical trial comparing focal photocoagulation to intravitreal corticosteroids (triamcinolone acetonide) for diabetic macular edema. However, even if triamcinolone or ranibizumab are proven to be efficacious, a major concern, based on clinical observations with intravitreal corticosteroids, is that DME will recur as the effect of the intravitreal drug wears off, necessitating repetitive injections long-term. Combining an intravitreal drug (triamcinolone or ranibizumab) with photocoagulation provides hope that one could get the short-term benefit of the intravitreal drug (decreased retinal thickening and decreased fluid leakage) and the long-term reduction in fluid leakage as a result of photocoagulation. In addition, it is possible that the worsening of macular edema immediately following focal photocoagulation, a known complication of this treatment, could be decreased if an intravitreal drug was present at the time of photocoagulation. This might result in an increased likelihood of vision improvement following photocoagulation and a decreased likelihood of vision loss.

This study is designed to determine if ranibizumab alone or ranibizumab added to laser photocoagulation is more efficacious than photocoagulation alone, and if so, to determine if combining ranibizumab with photocoagulation reduces the total number of injections needed to obtain these benefits. Furthermore, this study is designed to determine if combining photocoagulation with corticosteroids, the only other class of drugs currently being considered for treatment of DME, is efficacious in the population being enrolled.

Subjects will be randomly assigned to one of the following 4 groups:

1. Group A: Sham injection plus focal (macular) photocoagulation
2. Group B: 0.5 mg injection of intravitreal ranibizumab plus focal photocoagulation
3. Group C: 0.5 mg injection of intravitreal ranibizumab plus deferred focal photocoagulation
4. Group D: 4 mg intravitreal triamcinolone plus focal photocoagulation