Blockage of Central Retinal Vein

Sudden blindness or retinal vein occlusion; also see blockage of central retinal artery

Blockage of the retinal (membrane in the back of the eye) artery (carries oxygen-rich blood to retina) or retinal vein (carries oxygen-poor blood from retina) will lead to painless, Sudden Blindness in one eye in the case of an arterial (arteries) occlusion, and more gradual loss of central vision in a venous (veins) occlusion.

Sudden Blindness in one eye

Painless

Center of vision is affected

Parts other than center of vision can also be affected

Stroke

Glaucoma

Emboli -- pieces of clotted blood, tumor (Atrial Myxoma), plaque (fatty tissue in the arteries), fat, or vegetation (i.e., bacterial growth) on the heart valves (endocarditis) can travel through the blood stream via the arteries, arrive at the narrowed central retinal artery, and block the flow of the blood to the retina.

Blood clot (thrombus) can also form in the lumen of the retinal artery and, when large enough, block the flow.

Temporal Arteritis is another cause.

Other forms of vasculitis (e.g., lupus erythematosus)

History of symptoms, drugs, medications, illness, trauma, family history, Bruising
Medical exam:

The test most helpful is an ophthalmoscopic (a device with a light source that allows doctor to look inside the eye) examination, in addition to a general eye examination.
Using an ophthalmoscope reveals:

Pupil's abnormal enlargement or dilation (lack of normal response to light)
Cherry red spot and ground glass retina are some of the characteristic findings.
Retinal arteries are reduced in size.
Emboli or blood clots may be seen in the retinal arteries.

Tests:

Blood samples are sent for ESR, platelet count, blood cell count (red and white cells),Fibrinogen levels, antiphospholipid antibodies, PT/PTT, Protein Electrophoresis, glucose, and lipid levels.

Blood cultures to rule out infections, such as endocarditis.

ECG to diagnose heart arrhythmias.

Carotid Doppler studies to show plaques in the carotid arteries, which supply the retinal arteries.

Echocardiography will use sound to show bacterial vegetations or tumors of the heart.

Coagulopathies (e.g., blood flow or clotting problems) such as in Sickle Cell Anemia

Heart arrhythmias such as atrial fibrillation

Intravenous (in the veins) drug abuse

Heart tumors

Oral contraceptives

Retinal Vein Occlusion -- more common in elderly

Atherosclerotic vascular disease

Hypertension

Smoking

High cholesterol

Diabetes

Glaucoma

Male

Age > 60

Prolonged pressure on the eye, as in a comatose patient lying face down

An ophthalmologist (eye doctor) may be called in. Lowering the intraocular pressure to below 15 mm Hg is helpful and can be done by:

Applying direct pressure for 5-15 seconds may help to dislodge the emboli, but must be repeated several times.
Using a needle to remove some of the fluid inside the eye (anterior chamber paracentecis)

Hyperbaric oxygen (chamber where oxygen given under high pressure), carbogen (using carbon dioxide gas to dilate the blood vessels), or thrombolysis using medications to dissolve the clot -- may help if used within the first 6-12 hours of onset of blindness/symptoms.