Although central retinal vein occlusion (CRVO) is a common disorder, information on the natural history of visual outcome generally suffers from two fundamental flaws: it lumps ischemic and nonischemic cases together, or the criteria used to differentiate the two types of CRVO are inadequate. Also, the studies include only visual acuity data without any information about visual field outcomes.
The authors of this study sought to address these flaws by prospectively evaluating the natural history of visual outcome - both visual acuity and visual fields - as well as the factors that influence these outcomes by differentiating CRVO into ischemic and nonischemic types using a combination of functional and morphologic criteria. The data came from 667 consecutive patients with CRVO first presenting to the authors' clinic between 1973 and 2000. Eyes with ischemic CRVO had significantly worse initial visual acuity and visual field defects. Of the eyes first seen within three months of onset, 78 percent with nonischemic CRVO could see 20/100 or better compared with only 1 percent of patients with ischemic CRVO (P<0.0001). Visual field defects were minimal or mild in 91 percent of nonischemic CRVO patients and 8 percent of ischemic CRVO patients (P<0.0001).
Final visual acuity on resolution of macular edema was 20/100 or better in 83 percent of nonischemic patients, compared to 12 percent of ischemic patients (P<0.0001), while visual field defects were minimal or mild in 95 percent and 18 percent, respectively (P<0.0001).
Among eyes with an initial visual acuity of 20/70 or worse, 59 percent of nonischemic CRVO patients experienced an improvement in visual acuity following resolutions of macular edema, while no ischemic patient with an initial visual acuity of 20/70 or worse experienced significantly improved vision. Similarly, 86 percent of nonischemic CRVO patients with moderate to severe initial visual field defect improved, compared with no ischemic cases. In nonischemic CRVO, development of foveal pigmentary degeneration, epiretinal membrane, or both, was the main cause of poor final visual acuity. Visual outcome was influenced by several other factors, as well, including increasing age, cerebrovascular disease, diabetes mellitus, and, in ischemic CRVO, neovascular glaucoma.
The authors conclude that distinguishing between the two types of CRVO is crucial to determine visual outcomes. They advise that the most reliable method for differentiating between the two types during the initial acute phase are functional tests such as visual acuity, visual fields, relative afferent pupillary defect, and electroretinography. Morphologic tests, such as fluorescein fundus angiography and ophthalmoscopy, are much less reliable.