June 14, 2022
Retinal venous occlusions, or retinal vein thromboses, are the second most common retinal vascular disease after diabetic retinopathy.
This occlusive vascular disease has two forms. Central vein occlusion is generally accompanied by a sudden decrease in vision and loss of peripheral vision, which can be severe and unrecoverable in some cases. Occlusion of a branch of the central retinal vein, generally less severe, is accompanied in many cases by less severe loss of vision and loss of vision in the corresponding field (most commonly the lower field of vision, essential for walking and reading). Unfortunately, some cases of branch occlusion are severe and present with severe vision loss.
Age and hypertension are the main risk factors. Although 51% of people with this disease are over 65, no age is immune; in fact, 16% of central retinal vein occlusions happen in people under 45.
The cause of vision loss can be of two types: oedema (accumulation of fluid) in the central region of the retina, the macula, responsible for discriminating vision, and cell death due to lack of oxygen (ischemia) of the more peripheral retina, responsible for more peripheral vision. In some cases, fortunately infrequent, massive cell death of the nerve cells occurs in the more central area, causing permanent and serious loss of sight (legal blindness). From a legal point of view, both the assessment of central and field vision are required for the renewal of a driving licence and for obtaining incapacity for work.
The basis of treatment for these once devastating diseases is injections of drugs into the eye (intra-vitreous). It must be realised that once present, these diseases never go away, and are treated as chronic diseases, requiring periodic chronic treatment. In central vein occlusion, one can expect to need 10 injections in the first year, decreasing progressively to 6 injections in the fourth year and 4 injections in the eighth year after thrombosis. In branch occlusions a treatment with at least 7 injections in the first year can be expected. In a small number of cases, vision recovers completely without the need for treatment.
Response to treatment depends on promptness. The sooner the patient becomes aware of the loss of sight and contacts the doctor, the more likely it is that good visual acuity and field vision will be restored after treatment is started. As we have two eyes, loss of vision in one eye can go unnoticed for a relatively long time, so it is important to be aware of it. During treatment, especially when you start spacing out the injections, relapses can occur. Relapses present with the perception that the lines on a piece of graph paper (mathematical notebook) are shortening, followed by loss of vision. It is important to go immediately to the emergency department of the hospital where you are treated, as the delay in treatment and the number of relapses can mean the irrecoverable loss of a percentage of your vision.
Some more severe cases of occlusion of the central retinal vein and, more rarely, of one of its branches, may require retinal surgery or laser or cryotherapy (cold probe treatment) of the peripheral retina, usually several months or years after diagnosis, but it should be borne in mind that surgery only treats the most serious complications (growth of abnormal vessels and membranes in the retina) and is by no means the basis of treatment.
The best way to prevent these diseases is to control blood pressure (it is important to reduce the use of salt in food), weight and cholesterol. Physical exercise is an important aid. Once the disease has occurred, the best way to maintain stable vision is not to miss the injections scheduled by the ophthalmologist and to go to hospital as soon as you have a relapse, as described above.
It is rare that they lose their driving or reading vision and very rare that they develop into legal blindness or glaucoma if these guidelines are followed.
By António Campos, MD PhD.
