- Initially, patients with central retinal vein occlusion were not required to have previous therapy. However, the protocol was subsequently modified to require an intravitreal injection of triamcinolone acetonide > 12 weeks prior to study entry, with an initial decrease in macular edema and improvement in visual acuity and subsequent decline in visual acuity accompanied by increased macular edema. This modification was added to avoid enrolling patients who might have had a long-lasting response to a single intravitreal triamcinolone acetonide injection.