Central Retinal Vein Occlusion

Morphological Tests

Ophthalmoscopy: Most ophthalmologists tend to use this as the main criterion to find out the type of CRVO. It is usually felt that extensive retinal hemorrhages and cotton-wool spots suggest an ischemic CRVO. However, our experience and our studies showed that these are very unreliable parameters. In fact our studies have shown that ophthalmoscopy is the least reliable and most misleading test for such a differentiation. For example, the eye in Figure 4 ophthalmoscopically looks like non-ischemic CRVO, but by all other parameters, it was an ischemic CRVO. Similarly, the fundus appearance of the eye in Figure 5a, with massive hemorrhages and few cotton-wool spots, is highly suggestive of ischemic CRVO; but the visual field plotting in Figure 5b shows that the eye can still see I-2e, and has normal peripheral visual fields with I-4e. As I mentioned earlier, if an eye can see I-2e there is a very high chance that that eye has non-ischemic CRVO. Moreover, this eye could see almost 20/40 - 20/50 which is another parameter telling us that this eye is a non-ischemic CRVO, in spite of extensive hemorrhages and some cotton-wool spots, which are considered signs of an ischemic CRVO. Two years later, the fundus and the angiographic appearances were perfectly normal in that eye - Figure 6a shows the fundus is perfectly normal, and Figure 6b shows fluorescein fundus angiogram with no capillary obliteration and perfectly normal retinal vascular beds; Thus, in fact this was a non-ischemic CRVO, which ophthalmoscopy would have made us believe was ischemic CRVO. Thus, our study has shown that the ophthalmoscopic appearances can be similar in ischemic and non-ischemic CRVO, during both early and late stages of the disease, and can mislead us in diagnosis.

Figure 4.

Figure 5a	Figure 5b

Figure 6a	Figure 6b

Fluorescein Fundus Angiography: In fluorescein fundus angiography, typically the retinal capillary non-perfusion or obliteration is considered the diagnostic criterion of ischemic CRVO. Figure 7a is a fundus photograph and Figure 7b an angiogram of an eye with non-ischemic CRVO, and typically we see that all the capillary bed fills very well, and there are a few scattered retinal hemorrhages and engorged retinal veins.

Figure 7a	Figure 7b

Figure 8a	Figure 8b

In contrast to that, in Figure 8 there is almost total non-perfusion of the retinal capillary bed, indicating that this is an ischemic CRVO. If such good-quality angiogram of non-ischemic and ischemic CRVO is available, then fluorescein fundus angiography is very helpful. Unfortunately, there are multiple limitations in the evaluation of retinal capillary non-perfusion by fluorescein fundus angiography in CRVO, especially in fresh cases. These limitations include:

• During the very early stages, in spite of retinal ischemia, retinal capillary non-perfusion may not be seen, because it takes time for the retinal capillaries to obliterate completely. For example, in Figure 9a the retinal capillary bed filled very well when the eye was first seen within a week or two after the onset of the visual loss, in spite of being an ischemic CRVO by other parameters. However, when seen 2 months later, the retinal capillary bed was completely obliterated (Figure 9b). So the first angiogram (Figure 9a) would make us believe that we were dealing with a non-ischemic CRVO.

Figure 9a	Figure 9b

• If there are extensive retinal hemorrhages, as seen in Figure 10, it is usually almost impossible to evaluate capillary non-perfusion accurately, because of the masking effect by the blood.

Figure 10

• Poor quality angiograms in these patients are not uncommon because of media opacity due to cataracts (because most of these patients are elderly), or a small pupil (because many of them have glaucoma and have been on Pilocarpine for a long time), or poor circulation (because of cardiovascular disorders), or poor cooperation, or other causes.
• Inadequate sampling of the fundus is also a serious problem. We know that in diabetic retinopathy, CRVO and branch retinal vein occlusion, the earliest retinal capillary non-perfusion usually starts from the periphery and progresses toward the posterior pole. Conventional angiograms in these cases usually cover only the posterior pole, and miss extensive peripheral capillary non-perfusion. For example, in the eye shown in Figure 11a, the 60^o angiogram of the posterior pole shows the capillary bed to be fairly good. However, the periphery of that eye showed extensive areas of capillary non-perfusion and even neovascularization (Figure 11b), so that an angiogram of the posterior pole here would point to non-ischemic CRVO, when, in fact, the eye has definite ischemic CRVO.

Figure 11a	Figure 11b

Thus, our study showed that fluorescein fundus angiography provided information on retinal capillary non-perfusion in only 2/3 of the eyes during the acute phase because of various limitations listed above. Not only that, but also fluorescein fundus angiography provided misleading information in some. Therefore, in our study, overall, angiography performed much worse than any of the functional tests. No doubt, if we can get good-quality retinal capillary information from all over the retina, fluorescein angiography is the best test.

Fallacy of using “10 disc area of retinal capillary obliteration” as the criterion to define ischemic CRVO: Another very important misleading factor in the various studies in the literature differentiating ischemic from non-ischemic CRVO is the widely advocated use of a “10 disc area of retinal capillary obliteration” as the normal yardstick. Our studies have shown that this is usually an invalid criterion for diagnosis of ischemic CRVO by fluorescein angiography. A recent multicenter study⁴ on CRVO came to the same conclusion. The study results clearly showed that eyes with less than 30 disc diameters of retinal capillary nonperfusion and no other risk factor are at low risk for developing iris/angle NV, “whereas eyes with 75 disc diameters or more are at highest risk”. Thus “10 disc area of retinal capillary obliteration” is a poor and unreliable parameter in differentiating ischemic from non-ischemic CRVO as well as predicting ocular NV; and its use in many studies has resulted in misleading information and confusion.

see: Fundus photographic comparison of ischemic and non-ischemic CRVO (fig.12)