Frequency
Retinal vein occlusions can occur at any age, in adolescents as well as in the elderly, with an average age of onset between 55 and 65 years of age.
Mechanisms
Retinal vein occlusions are the result of a sudden slowing down of the venous circulation in the retina.
Depending on the site of obstruction, two clinical forms can be distinguished:
- in the optic nerve: occlusion of the central retinal vein (CRVO), or hemispherical occlusion in the case of a duplicated central vein;
- in the retina, at the level of an arteriovenous cross: occlusion of a retinal vein branch (OBVR).
When a venous occlusion occurs, the blood can no longer flow out of the eye normally: this results in a slowing of blood flow and high pressure in the veins. These phenomena are reflected in the fundus by dilation of the veins and the appearance of hemorrhages.
Two phenomena combine to bring down the vision:
- circulatory slowdown (which can lead to retinal pain due to lack of oxygen: ischemia);
- edema of the retina (macular edema),
these two phenomena are associated with degrees that vary according to the patients.
Cause
The cause of retinal vein occlusions is uncertain.
For occlusions of the central vein, it is possible that a clot forms in the central vein, but there is no certainty on this point.
The blood pressure is frequently found associated with occlusion of the central retinal vein, without one understands the relationship between the two diseases.
For venous branch occlusions, the mechanism is probably different. Simplifying, it seems that a small artery, whose wall is “hardened” (by arterial hypertension for example), “crushes” a vein at a cross between the two.
The glaucoma is also frequently associated with retinal vein occlusion.
Venous occlusions are different from phlebitis of the lower limbs (patients suffering from one have no more risk of suffering from the other disease … and vice versa!) And have no relationship with smoking (and probably not with hypercholesterolemia).
This disease could be genetic in some cases. Indeed, several cases can occur within the same family. However, the responsible gene has not been discovered to date.
It is very common to find no cause for the disease.
Diagnostic
Most often, the diagnosis is made by the ophthalmologist by examining the fundus.
Complementary examinations are most often limited to fundus photographs, and sometimes angiography (injection of the fluorescent product into the veins of the arm to better see the vessels of the retina).
A simple biological assessment can be proposed, for example, to look for a too high blood viscosity or a tendency to exaggerated coagulation; more thorough blood and cardio-vascular assessment is sometimes necessary, decided on a case by case basis.
It should be noted that this assessment is most often normal because there are few people in whom a general disease-related to venous occlusion is found, except for arterial hypertension and glaucoma.
Because of its potential complications, and to be able to propose a possible treatment in time, it is necessary to carry out regular ophthalmological checks.
Evolution and prognosis
Once declared, the course of the disease is difficult to predict.
Venous occlusion can last several months, and in some cases even become chronic (persisting for many years).
Either the occluded vein will spontaneously open, or vessels called “collateral vessels” will develop to circumvent the obstacle.
If these collateral vessels develop quickly enough, the circulation can be restored and thus the retinal lesions will be limited. The severity of the visual loss is thus very variable.
Many patients recover (spontaneously) without sequelae. On the other hand, in others, vision can remain impaired at different levels. There may be fluctuations in vision from one day to another, even during the same day (usually with poorer vision in the morning).
The most severe forms of the disease are essentially the result of certain occlusions of the central vein.
In contrast, loss of vision is never complete during branch occlusions because most of the retina is not affected by occlusion.
The risk of lateralization, although not zero, is very low.
Treatment
At present, there is little certainty about how to treat this disease.
- When vision is low due to prolonged edema of the retina, some treatments such as laser and/or intraocular injection of anti-inflammatory drugs (steroids or “cortisone”) or “anti-VEGF” drugs, can improve vision, at least for a few months. These treatments are not intended to “unclog” the veins, but to reduce macular edema: they can help recover vision until the venous circulation improves spontaneously.
- In certain severe forms (“ischemic”), that is to say, the cases in which the capillaries are blocked on a large surface, the realization of a laser treatment may be necessary, to avoid the proliferation of small abnormal vessels that may cause bleeding and/or pain. This laser treatment has no effect on visual acuity but can just avoid the occurrence of complications (sometimes painful) on an eye already visually impaired.