Posterior pole assessment will reveal retinal vessel tortuosity with dilated vessels. In these patients, acuity levels will be reduced to worse than 20/200. Ischemic CRVO also presents with unilateral sudden painless loss of vision. There is a 15% chance of going from a nonischemic to ischemic CRVO within the first 4 months, and a 34% chance of this occurring within 3 years. The patient’s vision usually returns to near-normal levels as long as it does not progress into an ischemic CRVO. Resolution of nonischemic CRVO often begins within 6 to 12 months. The patient’s visual acuity level will be better than 20/200, and examination of the posterior pole of the fundus will reveal dot/blot hemorrhages in all 4 quadrants with mild dilation and tortuosity of the vessels. Nonischemic CRVO often presents with unilateral sudden painless loss of vision. When assessing retinal vein occlusions, specifically CRVO, it is also important to classify the occlusion as either ischemic or nonischemic. If a patient with any of these conditions presents with a vein occlusion of the retina, it is important to consider that this patient is at a higher risk of having a future devastating systemic complication. Some of the most common conditions associated with vein occlusions include hypertension, diabetes, increased body mass index, generalized systemic vascular disease, glaucoma, autoimmune and inflammatory conditions, and clotting disorders. It is important to consider systemic health when examining a patient with a vein occlusion. If edema occurs within the macula, decrease in vision can be significant. This fluid can cause separation of the retinal layers, which causes vision loss. Edema results from leakage of fluid from the involved vasculature. Another cause of vision loss in vein occlusions is edema. Ultimately, this leads to permanent loss of vision. Ischemia causes areas of the retina to become nonfunctional due to a lack of nutrient supply. With each type of vein occlusion, the cause of the vision loss is due to damage of the vasculature, which ultimately leads to ischemia. If the occlusion occurs in larger veins, such as the central retinal vein, vision loss is often devastating and widespread, because the whole retina is involved. If the occlusion occurs in smaller veins of the retina, it is referred to as a BRVO, and vision loss may be less extensive. The origin of the occlusion and its effects depends on the area of occlusion. This blockage leads to hemorrhaging, damage of the retinal vessels, and ischemia. The stasis often results from thrombus formation due to an artery compressing a vein. When a vein occlusion occurs, it causes stasis of blood drainage within the eye. 1 While the incidence of these conditions is low, they can have devastating visual complications. One population-based study has reported the prevalence of CRVO as 0.1% and of BRVO as 0.6% of the population. Patients with these conditions usually present with a sudden painless loss of vision in one eye. Retinal vein occlusion is divided into 3 different types-central retinal vein occlusion (CRVO), hemiretinal vein occlusion (HRVO), and branch retinal vein occlusion (BRVO).
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