Central Retinal Vein Occlusion

Natural History of CRVO

For proper management of a disease, understanding the natural history of the disease is absolutely essential, so that the natural history may not be interpreted as a beneficial effect of the treatment being advocated. I have discussed elsewhere the following aspects of natural history of CRVO.⁶

1. Visual outcome: There is little definite information on the natural history of visual outcome in CRVO in the literature. The available information is based mostly on studies with either poor differentiation of ischemic from non-ischemic CRVO or none at all, most of them retrospective.^7,8,9 For example, the Multicenter CRVO study⁷ reported that initial acuity largely determines the visual acuity outcome, but in that study CRVO was not differentiated into the two types. This invalidates the findings, because it is like mixing apples and oranges.

In 1984, I analyzed the final visual acuity in 144 consecutive non-ischemic CRVO eyes with completely resolved retinopathy who were followed in my clinic up till 1984. Table 2 gives the final visual acuity achieved in these 144 eyes. There was a significant improvement of visual acuity, spontaneously, in eyes with initial visual acuity of 20/200 or better.

2. Ocular NV: As mentioned above, non-ischemic CRVO eyes do not develop NV unless there is associated disease that can cause NV, e.g., diabetes mellitus or ocular ischemia⁵. In ischemic CRVO:
   1. the risk of developing anterior segment NV exists mainly during the first 7-8 months of the disease,
   2. the maximum risk of developing NVG is about 45%, and
   3. current conventional wisdom is wrong in assuming that all eyes with iris or angle NV go on to develop NVG; 1/3 of eyes with iris NV and ¼ of eyes with iris and angle NV do not progress to develop NVG on follow-up (Fig. 15). These three facts of the natural history of ocular NV in ischemic CRVO are of great clinical importance in its management.
3. Cumulative chances of conversion of non-ischemic CRVO to ischemic CRVO during follow-up: In our series of 500 eyes with non-ischemic CRVO, from the time of onset of non-ischemic CRVO, this happened within 6 months in 9.4% and reached almost its maximum within 18 months in 12.6%.³
4. Resolution of retinopathy: In both types of CRVO, the retinopathy spontaneously resolves after a variable period. There is marked inter-individual variation in the time it takes to resolve - usually faster in younger than older people. Thus, both types of CRVO are self-limiting diseases, although during the period of activity they may produce various complications.