Retina is the light sensitive layer present at the back of the eye. It contains nerve cells which convert the focused image to an electrical signal which is then transmitted to the brain. These nerve cells require a continuous blood supply to meet their demand of oxygen and nutrients. Retinal layer is rich in blood vessels and supplies blood to the nerve cells. Blockage of the small veins that drain blood from the retina may occur because of formation of blood clots and atherosclerosis (hardened arteries). This disease condition of the eye characterised by the blockage of retinal vein by blood clot is called retinal vein occlusion.
Patients with high blood pressure, diabetes, high blood cholesterol levels or other vascular diseases are more prone to have retinal vein occlusion. In few cases it may also occur because of the presence of very narrow retinal veins. It mostly affects people above 60 years.
The symptoms include blurring of vision which may be mild at first but may progress slowly over time. In some cases, complete loss of vision may occur suddenly. The two main complications of retinal vein occlusion are macular oedema and neovascular glaucoma. In macular oedema the leakage of fluid from the blood vessels causes swelling of the retina that may lead to retinal detachment. Neovascular glaucoma refers to the growth of newer blood vessels in the retina with increase in pressure inside the eye. Both the eye complications if not treated timely may cause blindness.
Diagnosis involves detailed eye check up with visual acuity test, slit lamp examination, examination of the retina after pupil dilation, measurement of intraocular pressure. It may also involve retinal photography and fluorescein angiography to check for the growth of the new blood vessels in the eye. In fluorescein angiography, a fluorescein dye injection is given in the arm and the images are taken of the retina to visualise the blood vessels once the dye reaches the eye. To check for underlying disease causing retinal vein occlusion, blood tests for diabetes or levels of cholesterol in the blood may be asked for.
There is no treatment available to open up the blocked retinal veins but your doctor will treat the underlying disease or any current complication to prevent further deterioration of the vision. Through medications, high blood pressure, diabetes or high blood cholesterol levels are kept under control. The complication, macular oedema is treated with focal laser photocoagulation and neovascular glaucoma is treated with panretinal laser photocoagulation.
Laser photocoagulation uses laser beam to burn the abnormal blood vessels in the retina. Thus no more leakage of fluid occurs from the blood vessels and it also prevents their further growth. Another method of treatment for neovascular glaucoma which is under study is injection of anti-vascular endothelial growth factor in the eye. It inhibits the abnormal growth of new blood vessels.