Retinal vein occlusion refers to the closure of the central retinal vein that drains the retina or to that of one of its branches.
Description
Retinal vein occlusion (RVO) occurs when the central retinal vein, the blood vessel that drains the retina, or one of its branches becomes blocked. RVO may be categorized by the anatomy of the occluded vein and the degree of ischemia produced. The two major RVO types are central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO). CRVO has been diagnosed in patients as young as nine months to patients of 90 years. The age of affected individuals is usually low to mid 60s. Approximately 90% of patients are over 50 at the time of diagnosis, with 57% of them being male and 43% being female. BRVO accounts for some 30% of all vein occlusions.
Causes and symptoms
CRVO is a painless loss of vision that can be caused by a swollen optic disk, the small area in the retina where the optic nerve enters the eye, by dilated retinal veins, and by retinal hemorrhages. CRVO is also called venous stasis retinopathy, or hemorrhagic retinopathy.
In BRVO, the superotemporal branch vein is the most often affected vessel. Retinal hemorrhages follows, often occurring at the crossing of two vessels near the optic disk. Initially the hemorrhage may be extensive and underlie the fovea.
The exact cause of RVO is not yet identified, but the following mechanisms been proposed:
external compression between the central connective strand and the cribriform plate
A complete physical evaluation is recommended for CRVO and BRVO, including complete blood tests, and glucose tolerance test (for non-diabetics). In the case of a head injury when bleeding around the optic nerve is a possibility, an MRI may be performed.
Treatment
Following a patient with RVO is vital. Patients should be seen at least monthly for the first three months to monitor for signs of other complications, such as the abnormal formation of blood vessels (neovascularization) in the iris of the eye or glaucoma.
The treatment for retinal vein occlusion varies for each case and should be given based on the doctor's best recommendation. Although treatments for occlusion itself are limited, surgical treatment of the occlusion provides an option.
Treatments may include anticoagulants with heparin, bishydroxycoumarin, and streptokinase. When the blood is highly viscous, dilution of the blood may be useful. Ideally, an alternate pathway is needed to allow venous drainage. Recent reports published in 1999 suggest that use of a laser to create a retinal choroidal hole may be useful to treat CRVO. Laser therapy depends on the type of occlusion. The management of laser therapy should be controlled by an ophthalmologist.
Alternative treatment
There are no documented alternative treatment methods.
Prognosis
The outlook for people with RVO is fairly good whether it is treated early or not. With no treatment at all, approximately 60% of all patients recover 20/40 vision or better within a year.
Prevention
Retinal vein occlusion is difficult to prevent because the exact cause is still uncertain. Ethnic factors may play a role since in the UK the disease is rare in Asians and West Indians.
BOOKS
Newell, Frank W. Ophthalmology Principles and Concepts, 8th Ed. Boston: Mosby-Year Brook Inc., 1996.
Spaide, Richard F., MD. Diseases of the Retina and Vitreous. New York: W.B. Saunders Co., 1999.
Michael Sherwin Walston
Ronald Watson, PhD
KEY TERMS
Anticoagultants—Drugs that act by lowering the capacity of the blood to coagulate, thus facilitating removal of blood clots.
Central retinal vein—Central blood vessel and its branches that drains the retina.
Cribriform plate—The horizontal bone plate perforated with several holes for the passage of olfactory nerve filaments from the nasal cavity.
Fovea—A small area of the retina responsible for acute vision.
Glaucoma—A group of eye diseases characterized by an increase in eyeball pressure.
Hyperlipidemia—A general term for elevated concentrations of any or all of the lipids in the plasma.
Iris—The contractile diaphragm located in the fluid in front of the lens of the eye that is perforated by the eye pupil.
Ischemia—A state of low oxygen in a tissue usually due to
Neovascularization—Abnormal or excessive formation of blood vessels as in some retinal disorders.
Occlusion—Momentary complete closure of some area or channel of the body.
Optic disk—The small area in the retina where the optic nerve enters the eye that is not sensitive to light. Also called the blind spot.
Retina—Light sensitive layer of the eye, that consists of four major layers: the outer neural layer, containing nerve cells and blood vessels, the photoreceptor layer, a single layer that contains the light sensing rods and cones, the pigmented retinal epithelium (PRE) and the choroid, consisting of connective tissue and capillaries.
