Over the past few months, I have been following a patient who was unlucky to have bilateral (both eyes) branch vein occlusions, but lucky that neither has affected her vision.
How can that be?
Most of the time, a healthy patient may notice sudden vision loss in one eye. Vision loss due to a BRVO is painless and occurs all of the sudden.
There are two types of retinal vein occlusions:
The mechanism is the same and the two differ mainly by the amount of retina involved. The CRVO affects the entire retina whereas the BRVO affects half the retina or less.
Vision loss depends depends upon whether or not the macula is involved. If the macula, the functional center of the retina, is involved, then there is usually noticeable vision loss.
In most cases, patients can no longer read when the macula is involved in cases of BRVO.
Though I don’t want to get into too much detail, patients with CRVO have much worse vision and the prognosis is not nearly as good compared to BRVO with regard to visual recovery.
As you look at the image, the areas involved are limited to the areas with the streaks of blood. The blood leeches due to the corresponding vein becoming occluded.
Think of stepping on a garden hose. Your foot is the point of occlusion and water will leak out between the spigot and your foot.
If this area of involvement includes the macular (which neither does), then significant vision loss is noticed.
Look carefully and notice that neither macula is involved. The macula is normally darker as in these pictures. The blood is just outside of the macula….explaining why there is no vision loss and, in fact, the patient is completely unaware of anything wrong.
Treatments are available if macular edema develops from a BRVO.
This does not happen very often.