RETINAL VEIN OCCLUSION

SIGNS AND SYMPTOMS
The patient will usually be elderly, often with a history of systemic diseases such as diabetes and hypertension. The patient may be asymptomatic, but often will complain of sudden painless unilateral loss of vision and/or visual field, and may complain of a sudden onset of floating spots or flashing lights. Acuity may range anywhere from 20/20 to finger counting. If vision loss is severe, there may be a relative afferent pupillary defect.

Ophthalmoscopically, there will be retinal edema, superficial hemorrhages, disc swelling, cotton wool spots, and tortuous and dilated retinal veins. If there is a central retinal vein occlusion, these findings will encompass all four retinal quadrants. A hemi-central retinal vein occlusion will involve only the superior or inferior half of the retina. A branch retinal vein occlusion will present with findings in only one quadrant, usually supero-temporal, with the apex of the hemorrhage at an arteriovenous crossing.

The hemorrhaging may be so severe that all features of the underlying retina are obscured. Multiple cotton wool spots indicate retinal ischemia and capillary non-perfusion. Anterior and posterior segment neovascularization may occur later in the disease.

PATHOPHYSIOLOGY
The etiology of central and hemi-central retinal vein occlusion is an obstruction of the central retinal vein, or one of the vein's two trunks, as it constricts through the lamina cribrosa. The cause is obscure, but may involve abnormal blood flow or blood constituents, atherosclerosis, vessel anomalies or a combination of these factors.

The etiology of a branch retinal vein occlusion is an arteriolosclerotic arteriole crossing and constricting the underlying venule. This will result in leakage from the capillary beds draining into these vessels. The capillary beds may be irreversibly damaged by this leakage, resulting in perpetual non-perfusion of the retinal tissue. If a significant area of capillary non-perfusion is present, then the occlusion is considered ischemic.

Loss of retinal capillary beds with subsequent retinal non-perfusion will lead to retinal hypoxia and the subsequent release of vasoproliferative substance. Vasoproliferative factors will then stimulate the proliferation of neovascularization from nearby viable capillary beds.

In branch and hemi-central occlusions, neovascularization will most often form on the optic disc or adjacent retina and can lead to vitreous hemorrhage and tractional retinal detachment. In central retinal vein occlusions, the closest viable capillary network from which neovascularization will form is typically the posterior iris. This can lead to rubeosis irides and neovascular glaucoma. In all cases of venous occlusion, the main cause of vision decrease is macular edema. However, if retinal capillary non-perfusion involves the perifoveal region, then vision is dramatically and irreversibly lost.

MANAGEMENT
Fluorescein angiography, long held to be the gold standard in assessing retinal vascular disease, has questionable use in vein occlusions. It is not indicated initially, as the fresh hemorrhage will block transmission and reveal no useful information, but later in the disease it will provide information about retinal capillary perfusion and whether or not the occlusion is ischemic and thus more likely to foster neovascularization. New research indicates that ischemic retinal vein occlusions do not benefit from prophylactic PRP; withhold this procedure until the patient develops frank neovascularization of the iris, disc or retina.

Monitor the patient monthly with serial ophthalmoscopy, fundus photography and goniscopy until you see resolution. If the patient has a hemi-central or branch retinal vein occlusion and vision is below 20/40 due to macular edema, the patient will benefit from focal laser photocoagulation anywhere between three and 18 months after the occlusion's onset. Central retinal vein occlusion patients with vision reduction due to macular edema do not benefit from the proceudre, according to new research.

Due to the association of systemic disease with vein occlusions, co-manage the patient with an internist. Tests to be ordered include: blood pressure, fasting blood glucose, lipid and cholesterol studies, FTA-ABS, complete blood count with differential, sickle dex (if the patient is African-American), anti-nuclear antibodies, angiotensin converting enzymes, and viscosity studies.

CLINICAL PEARLS

Ischemic vein occlusions are the only vein occlusions that will likely develop neovascular complications, and they account for only one-third of all occlusions.

Ischemic vein occlusions typically present with acuity worse than 20/200. Those eyes with initial acuity better than 20/200 are at very low risk of developing severe, permanent vision loss, and are likely to resolve.

Ischemic occlusions are likely to present with a relative afferent pupillary defect. If not, then it is likely non-ischemic.