Purpose
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To determine whether
photocoagulation therapy can help prevent iris neovascularization in eyes
with central vein occlusion (CVO) and evidence of ischemic retina.
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To assess whether
grid-pattern photocoagulation therapy will reduce loss of central visual
acuity due to macular oedema secondary to CVO.
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To develop new
data describing the course and prognosis for eyes with CVO.
Background
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.
Description
Eligible patients
were divided into four groups:
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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.
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Group M:
Eyes with visual loss ascribable to macular oedema were randomly assigned
to receive grid-pattern photocoagulation or nontreatment.
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Group P:
Eyes with relatively perfused retinas were followed to provide information
about the natural history of the disease.
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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.
Results
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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.
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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.
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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.
Publications
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The Central Vein
Occlusion Study Group: Natural history and clinical management of central
retinal vein occlusion. Arch Ophthalmol 115: 486-491, 1997.
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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.
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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.
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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.
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The Central Vein
Occlusion Study Group: Baseline and early natural history report. Arch
Ophthalmol 111: 1087-1095, 1993.
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