Central Vein Occlusion Study (CVOS)


  • To determine whether photocoagulation therapy can help prevent iris neovascularization in eyes with central vein occlusion (CVO) and evidence of ischemic retina. 
  • To assess whether grid-pattern photocoagulation therapy will reduce loss of central visual acuity due to macular oedema secondary to CVO.
  • To develop new data describing the course and prognosis for eyes with CVO.


Central vein occlusion is a common retinal vascular disorder with potentially blinding complications. The two major complications are reduced central vision caused by macular oedema and neovascular glaucoma caused by iris neovascularization. Other clinical trials have shown that laser photocoagulation is an effective treatment for complications found in diabetic retinopathy and branch vein occlusion, which have some features in common with CVO: neovascularization and reduced visual acuity caused by macular oedema occur in all three disorders. Evidence from small-scale studies suggests that a grid pattern of photocoagulation reduces macular oedema in CVO patients, although the associated changes in visual acuity are variable. The CVOS is a detailed investigation of grid pattern photocoagulation in a larger randomized group of patients.


Eligible patients were divided into four groups:
  • Group N: Eyes with extensive retinal ischemia (at least 10 disc areas of nonperfusion) were randomly assigned to receive panretinal photocoagulation or nontreatment unless iris neovascularization developed. 
  • Group M: Eyes with visual loss ascribable to macular oedema were randomly assigned to receive grid-pattern photocoagulation or nontreatment.
  • Group P: Eyes with relatively perfused retinas were followed to provide information about the natural history of the disease.
  • Group I: Indeterminate eyes in which the retina could not be visualized accurately because of hemorrhage were followed in a natural history study.

Green argon laser with a slit lamp delivery system was used for all treatments. Photographic documentation of retinal changes was obtained at entry, post-treatment, and at specified followup visits for a period of at least 3 years. The frequency of followup visits varied according to the group to which the CVO patient was assigned. Visual acuity, the primary outcome factor in the group with macular oedema, was measured according to a modified Early Treatment Diabetic Retinopathy Study protocol at each visit. 

Patient Eligibility

Men and women must have been age 21 or older and willing to return for followup visits for 3 years following assignment into the appropriate group and randomization. Each of the four groups has specific eligibility criteria. Patients with retinal vascular disease other than that specified in the criteria, such as diabetic retinopathy, were ineligible. Patients with macular disease other than that due to CVO were ineligible for that portion of the study.


  • Group M--Macular Oedema: Macular grid photocoagulation was effective in reducing angiographic evidence of macular oedema but did not improve visual acuity in eyes with reduced vision due to macular oedema from CVO.
  • Group N--Panretinal Photocoagulation for Nonischemic CVO: Prophylactic panretinal photocoagulation did not prevent the development of iris neovascularization in eyes with 10 or more disc areas of retinal capillary nonperfusion confirmed by fluorescein angiography. Rather, results of this randomized clinical trial demonstrate that it is safe to wait for the development of early iris neovascularization and then apply panretinal photocoagulation.
  • Group I--Indeterminate: Eyes with such extensive intraretinal hemorrhage that it is not possible to determine the retinal capillary perfusion status act as if they are ischemic or nonperfused.


  • The Central Vein Occlusion Study Group: Natural history and clinical management of central retinal vein occlusion. Arch Ophthalmol 115: 486-491, 1997.
  • The Central Vein Occlusion Study Group: Evaluation of grid pattern photocoagulation for macular edema in central vein occlusion. The CVOS Group M Report. Ophthalmol 102: 1425-1433, 1995.

  • The Central Vein Occlusion Study Group: A randomized clinical trial of early panretinal photocoagulation for ischemic central vein occlusion. The CVOS Group N Report. Ophthalmol 102: 1434-1444, 1995.
  • Clarkson JG, Central Vein Occlusion Study Group: Central vein occlusion study: Photographic protocol and early natural history. Trans Am Ophthalmol Soc 92: 203-215, 1994.
  • The Central Vein Occlusion Study Group: Baseline and early natural history report. Arch Ophthalmol 111: 1087-1095, 1993.
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