Pretutorial
Tutorial
Introduction
Pathophysiology
Classification
Complications
Differential Diagnosis
Management
Hemicentral Retinal Vein Occlusion
References
Bibliography
Central Retinal Vein Occlusion
Paul B. Greenberg, MD · Adam Martidis, MD
Central retinal vein occlusion (CRVO) is one of the most common retinal vascular disorders. The Beaver Dam Eye Study found that CRVO had a prevalence of 0.1% and a 5-year incidence of 0.2%.1 It typically presents as painless loss of vision in patients older than 50 years of age. Often, patients will have a history of glaucoma or systemic disease such as hypertension or diabetes mellitus. There are many less common conditions associated with CRVO including oral contraceptive use, homocysteinemia, platelet abnormalities, and abnormal blood viscosity, although most have not been systematically studied in large clinical trials.
The diagnosis of CRVO can usually be made based on characteristic ophthalmoscopic findings including retinal hemorrhage in all
quadrants, dilated and tortuous veins, and cotton-wool spots (Slide 1). Two significant vision-threatening complications are persistent
macular edema and neovascular glaucoma.
Through histopathological studies of eyes with CRVO researchers have documented thrombosis at the level of the lamina cribrosa. The mechanism of thrombosis is not well understood. Compression of the central vein in this region may increase turbulence and slow blood flow, leading to endothelial damage and thrombus formation. Arterial disease may also be an important factor. In the region of the lamina cribrosa (unlike other areas of the optic nerve), the central artery and vein share a common tunic of connective tissue, rendering the thin-walled vein vulnerable to compression by an artery thickened and hardened by arteriosclerosis and hypertension. Compression and distortion of the lamina cribrosa may also occur by other mechanisms such as elevated intraocular pressure or papilledema. Ultimately, venous occlusion causes slowing of blood flow with resultant hypoxia, endothelial cell damage, and disruption of the blood-retina barrier. These factors, in turn, influence the degree of retinal ischemia and macular edema seen clinically. The location of the venous thrombosis may also be a critical factor; occlusion posterior to the lamina cribrosa may decrease ischemia by facilitating the development of collateral circulation.
There are two types of CRVO: ischemic and nonischemic (75% of all cases are nonischemic). Classifying the type of CRVO during
the acute phase can be challenging. However, functional tests (visual acuity, visual fields, relative afferent pupillary defects, and
electroretinography) and morphological tests (ophthalmoscopy and fluorescein angiography) can usually distinguish between ischemic
and nonischemic cases. Eyes with ischemic CRVO are more likely to have visual acuity less than 20/200, relative afferent pupillary defects,
decreased visual fields, diminished b-wave amplitudes on electroretinography, and extensive nonperfusion on fluorescein angiography
(Slide 2A and Slide 2B ).
Distinguishing between the two types of CRVO is clinically important. Eyes with ischemic CRVO have a poor natural history: 67%
Functional testing is more reliable than morphological testing in the acute phase. Baseline visual acuity is an excellent predictor
of the risk for developing anterior segment neovascularization. Except for the presence of extensive retinal hemorrhages in the first 3
will develop ocular neovascularization and 37% will develop neovascular glaucoma. In eyes with nonischemic CRVO, the incidence of
ocular neovascularization is minimal, typically occurring only in the setting of severe occlusive carotid artery disease. However, these eyes
must still be followed closely, because up to one-third become ischemic over 3 years.
Macular edema is also a significant vision-threatening complication of CRVO (Slide 3, Slide 4A, Slide 4B,and Slide 5). At 3 years of follow-up, 60% of eyes with perfused CRVO and chronic macular edema will have visual acuity of 20/125 or less.
The diagnosis of CRVO is usually straightforward based on its characteristic ophthalmoscopic findings. However, it is important to consider other causes of diffuse retinal hemorrhages including diabetic retinopathy, ocular ischemic syndrome, radiation retinopathy, hypertensive retinopathy, and Purtscher retinopathy. Conditions such as papilledema or carotid-cavernous fistula that may result in secondary CRVO must also be ruled out.
The Central Vein Occlusion Study (CVOS; Table) reported that panretinal photocoagulation (PRP) in ischemic CRVO does not prevent the development of iris or angle neovascularization.2-5 Thus, both nonischemic CRVO and ischemic CRVO without anterior segment neovascularization should be managed through careful observation (the former to monitor for progression to ischemic CRVO). These examinations should ideally include gonioscopy in undilated eyes because neovascularization of the angle can precede rubeosis.
Once anterior segment neovascularization is detected, PRP should be performed promptly. In the CVOS, PRP-induced regression occurred in more than 90% of cases and lowered the risk of uncontrolled neovascular glaucoma to 1%. Eyes with ischemic CRVO that develop disc or retinal neovascularization (5% to 7%) should also receive PRP.
There is no proven treatment for macular edema secondary to CRVO. In the CVOS, focal grid photocoagulation was not effective in improving visual acuity in eyes with macular edema secondary to perfused CRVO, though there was a trend in patients younger than 60 years.
The overall visual prognosis in eyes with CRVO is directly related to baseline visual acuity. After 3 years of follow-up, 65% of eyes with initial visual acuity of 20/40 or better retain their vision, whereas 79% of eyes with initial visual acuity less than 20/200 fail to gain visual improvement. Patients with CRVO also have a 1% annual risk for developing a vascular occlusion in their fellow eye.
Although a variety of systemic diseases have been associated with CRVO, a work-up beyond a general medical evaluation is
usually unnecessary. In patients presenting with bilateral CRVO (< 0.5% of cases), an evaluation to rule out a hyperviscosity syndrome
should be considered.
Hemicentral Retinal Vein Occlusion
In up to 20% of eyes, two separate trunks of the central retinal vein (CRV) may enter the lamina cribrosa independently and then
join to form a central vein in the retrolaminar portion of the optic nerve (Slide 6A, Slide 6B,
and Slide 6C). In this congenital anomaly, thrombosis can occur in one
of the venous channels. The corresponding fundus changes involve the area supplied by the trunk, which is typically the superior or inferior
portion of the retina. This hemicentral retinal vein occlusion (RVO) is therefore clinically and pathogenetically related to a CRVO. In eyes
with hemicentral RVO, neovascular glaucoma occurs in 3%, iris neovascularization in 13%, and retinal neovascularization in 42%.
Although not studied prospectively in a large clinical trial, the management of neovascularization in these eyes should follow CVOS
guidelines with regard to the use of PRP. The role of grid laser photocoagulation for macular edema in hemicentral RVO is unclear.
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- Central Vein Occlusion Study Group. Baseline and early natural history report. Arch Ophthalmol. 1993;111:1087-1095.
- Central Vein Occlusion Study Group. Natural history and clinical management of central vein occlusion. Arch Ophthalmol. 1997;115:486-491.
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Finkelstein D. Ischemic macular edema: Recognition and favorable natural history in branch vein occlusion. Arch Ophthalmol. 1992;110:1427-1434.
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Hayreh SS, Zimmerman MB, Poldajsky P. Incidence of various types of retinal vein occlusion and their recurrence and demographic characteristics. Am J Ophthalmol. 1994;117(4):49-441.
Hayreh SS, Klugman MR, Beri M, Kimura A, Patricia Podhajsky. Differentiation of ischemic and non-ischemic central vein occlusion during the early acute phase. Graefe’s Arch Clin Exp Ophthalmol. 1990;228:201-217.
Hayreh SS, Zimmerman B, McCarthy MJ, Podhajsky P. Systemic diseases associated with various types of retinal vein occlusion. Am J Ophthalmol. 2001;131:61-77.