Central Retinal Vein Occlusion

Complications of CRVO

NON-ISCHEMIC CRVO: Long-term blinding complications are rare in this type. The major complication is chronic macular edema (Figure 13), leading on to cystoid macular degeneration, and permanent central scotoma; however, the peripheral visual field always remains normal. In about 12% of the eyes, within 18 months of onset non-ischemic CRVO may change to ischemic CRVO - more often in older than in younger persons³. If an eye with non-ischemic CRVO has a cilioretinal artery, then that eye develops cilioretinal artery occlusion (Figure 14) and an associated visual field defect and may produce sectoral optic atrophy.

Figure 13

Figure 14

ISCHEMIC CRVO: There are many serious complications in this type. The most important complication is the development of ocular neovascularization, with neovascular glaucoma as the most dreaded complication. It is seen only in ischemic CRVO, and the overall incidence in our series was about 45% among the ischemic CRVO eyes. Other complications of ischemic CRVO are vitreous hemorrhage, macular degeneration, optic atrophy, retinitis proliferans, phthisis bulbi or loss of eye.

Ocular neovascularization⁵: As I mentioned earlier, 81% of the patients with CRVO have the non-ischemic type, and only 19% have the ischemic type, and ocular neovascularization attributable to CRVO does not occur in non-ischemic CRVO; There are, however two exceptions to this: i.e. eyes with associated (a) ocular ischemia and (b) background diabetic retinopathy, because some of these eyes, in spite of having non-ischemic CRVO, may develop ocular neovascularization. In ischemic CRVO the neovascularization is mainly of the anterior segment. Figure 15 is a graphic representation of cumulative chances of developing various types of neovascularization (NV) in ischemic CRVO.

Figure 15 (click image for enlargement)

On the X axis are the days from the onset of ischemic CRVO, and on the Y axis is the cumulative chance or probability of developing neovascularization. The various graphs are, from above down, for iris neovascularization, angle neovascularization, neovascular glaucoma, disc neovascularization and retinal neovascularization, These graphs provide very important information on a number of issues, including the following:

• Not every eye with ischemic CRVO develops ocular neovascularization because it depends upon the severity of retinal ischemia - more the ischemia, higher the chances of developing neovascularization.
• When ocular neovascularization develops, the commonest site is the anterior segment, much less frequently the posterior segment.
• The greatest risk of developing anterior segment neovascularization is during the first 7 months, after which the risk falls dramatically to minimal. This is extremely important information in the management of these cases; they need to be monitored very frequently during the first 7 months and if they do not develop neovascularization of the anterior segment during this period, then the risk of neovascular glaucoma drops to minimum.
• The commonly held belief that every eye with CRVO that develops iris neovascularization or angle neovascularization is destined also to develop neovascular glaucoma is wholly wrong. In fact, about one-third of the eyes with iris neovascularization and about one-quarter of the eyes with both iris and angle neovascularization never develop neovascular glaucoma.

In order to place ocular neovascularization in overall CRVO in true perspective, it is important to point out two important facts: (i) Ischemic CRVO constitutes only one fifth of all CRVO cases. (ii) neovascular glaucoma, the most dreaded complication of CRVO, is seen at the maximum in about 45% of ischemic CRVO cases only. This would indicate that the overall incidence of neovascular glaucoma in the entire CRVO group is only 8 - 10% at the maximum - a highly important fact in any management considerations for CRVO.

Vitreous hemorrhage: In CRVO this may be either secondary to retinal/optic disc neovascularization or due to rupture of the blood through the internal limiting membrane, particularly in eyes with many sub-internal limiting membrane hemorrhages. In my experience, the latter source of vitreous hemorrhage is much more common than the former, and can occur in non-ischemic as well as ischemic types of CRVO, usually during the early stages of the disease. Vitreous hemorrhage from retinal/disc neovascularization usually occurs during the late stages of the disease. Sometimes the vitreous hemorrhage can occur from intraretinal microvascular abnormalities secondary to CRVO or development of posterior vitreous detachment. Therefore, it is important to be aware of the fact that the presence of vitreous hemorrhages in CRVO does not always mean the presence of retinal/disc neovascularization.