Retinal vein occlusion: Epidemiology, clinical manifestations, and diagnosis

INTRODUCTION — 

Retinal vein occlusion (RVO) is an obstruction of the retinal venous system. It is an important cause of visual loss among adults worldwide [1,2].

The epidemiology, clinical manifestations, and diagnostic evaluation of RVO will be discussed here. The treatment of RVO, as well as issues related to retinal artery occlusion, are discussed separately. (See "Retinal vein occlusion: Treatment" and "Central and branch retinal artery occlusion".)

CLASSIFICATION AND PATHOPHYSIOLOGY — 

RVOs are classified by the anatomic location of the occlusion, which has prognostic implications (visual acuity and other outcomes). From proximal to distal with respect to the central retinal vein, the classifications are (figure 1):

●Central retinal vein occlusion (CRVO) – CRVO occurs when a thrombus forms at the level of the lamina cribrosa (the connective tissue "sieve" through which the nerve fibers of the retina pass through to the optic nerve) [3]. The entire retina is affected (picture 1).

CRVO is further classified as ischemic or nonischemic (perfused), depending on the degree of retinal venous obstruction and perfusion of the retina. If collateral (optociliary) vessels later form between the central retinal vein and peripapillary choroid, the degree of retinal ischemia is generally reduced. These collateral vessels can sometimes be seen extending from the center of the optic disc to the disc margin. Venous obstruction located more anteriorly in the lamina cribrosa (distally and closer to the retina) probably interfere with such collateral formation, accounting for the relatively poor visual outcome compared with obstruction in the posterior lamina cribrosa. Eyes with more ischemia have worse visual impairment and higher risk of neovascularization of the iris and retina. (See 'Ocular neovascularization' below.)

●Hemiretinal vein occlusion (HRVO) – HRVO occurs when the superior and inferior retinal drainage does not merge into a single central retinal vein and one of the two trunks is occluded (generally more similar to CRVO than BRVO). One-half of the retina is affected (picture 2). The pathophysiology of HRVO is presumed to be similar to CRVO, but with greater potential for collateralization within the retinal circulation, a smaller area of affected retina, and a correspondingly lower potential for severe nonperfusion and ischemia.

●Branch retinal vein occlusion (BRVO) – BRVO occurs when a vein in the distal retinal venous system is occluded, most often due to compression by an overlying arteriole, leading to hemorrhage along the distribution of a small vessel of the retina (picture 3). The pathophysiology of BRVO is different from that of CRVO and HRVO. In BRVO, the inflexible, atherosclerotic arteriole is hypothesized to deform the relatively distensible veins (contained in an inelastic arteriovenous sheath) at arteriovenous crossings, resulting in a venous occlusion [3-5]. The increased incidence in the superotemporal quadrant is thought to be due to increased arteriovenous crossings in that quadrant. Several studies have suggested that the risk is greater among eyes where the retinal artery is anterior to the retinal vein [6-8].

EPIDEMIOLOGY

Prevalence — RVO is the second most common cause of vision loss from retinal vascular disease, after diabetic retinopathy [9]. The prevalence increases with age (0.7 percent at <60 years and 4.6 percent ≥80 years in one study [10]).

Branch retinal vein occlusion (BRVO) is most common, followed by central retinal vein occlusion (CRVO), and hemiretinal vein occlusion (HRVO), which is relatively rare and less well studied [1,2]. In a population cohort of adults in the United States, the 15-year cumulative incidence of BRVO and CRVO was 1.8 and 0.5 percent, respectively [11,12].

Risk factors — Risk factors for RVO include [5,9,13-18]:

●Older age

●Hypertension

●Diabetes (associated with CRVO but not BRVO)

●Cardiovascular disease

●Smoking

●Obesity

●Hypercoagulable state, particularly factor V Leiden and activated protein C resistance

●Hyperlipidemia

●Open-angle glaucoma (particularly for CRVO)

●Retinal artery abnormalities

Thrombophilic risk factors, such as factor V Leiden, may be more prevalent in younger patients, particularly those who are healthier and do not have the age-related cardiovascular risk factors listed above [19].

CLINICAL PRESENTATION

Symptoms — RVO is painless because the retina has no trigeminal innervation. Symptoms depend on the location of the RVO.  

●CRVO usually presents with the acute onset of blurred vision in one eye, which may be severe.

●HRVO usually presents with blurred central vision because the occlusion typically involves the macula, causing macular edema. Time of edema and symptom onset can be highly variable (days to weeks).

●BRVO may be asymptomatic, or may present with peripheral visual field defects (scotoma) in the affected eye, with blurred or gray vision corresponding to the area of occlusion. Macular edema may also cause visual acuity and visual field impairment that appears days to weeks after onset.

Ophthalmology referral — Primary care providers who evaluate patients with sudden visual loss (any change in visual acuity or visual field defects) should urgently refer the patient to an ophthalmologist, either in-office, or via an emergency care facility with ophthalmology support. If the diagnosis is uncertain, the patient should be instructed to avoid oral intake until cleared by the ophthalmologist since other conditions requiring urgent surgical intervention may also cause sudden visual loss.

Prior to referral, the initial basic eye examination, including visual acuity (using the patient’s most recent pair of eyeglasses), should be performed. Information from the basic examination assists the ophthalmologist in appropriate triage and evaluation (see 'Eye examination and findings' below). Pharmacologic dilation of the pupils should be avoided to allow the ophthalmologist to assess for a relative afferent pupillary defect and for rubeosis of the iris or anterior chamber angle.

EVALUATION AND DIAGNOSIS

When to suspect RVO — RVO should be suspected in older patients, particularly those over age 50, with hypertension or cardiovascular disease, who present with sudden, painless, severe visual loss involving one eye. RVO should also be suspected in asymptomatic such patients with suggestive findings on routine examination of the ocular fundus (eg, retinal hemorrhage, edema, dilated retinal venules, and cotton wool spots throughout the distribution of the affected vein). (See 'Symptoms' above and 'Eye examination and findings' below.)

History — The ocular history should determine whether the patient is experiencing pain, decrease in vision, or visual field deficits. Comorbid conditions should be documented, particularly cardiovascular risk factors that may predispose to RVO. (See 'Risk factors' above and 'Testing for underlying cardiovascular disease and hypercoagulability' below.)

Eye examination and findings — The initial basic eye examination can be performed by a general practitioner and includes evaluation of visual acuity, extraocular motility, pupillary function, and confrontation visual fields. The presence of any injection/redness of the conjunctiva and sclera should also be noted. A slit lamp and dilated fundus examination are deferred to the ophthalmologist. Typical findings are described below. Note that while these findings can be observed in RVO, care must be taken to consider other causes. (See 'Differential diagnosis' below.)  

●Basic examination – General practitioners should be able to perform the basic components of the examination, without the aid of advanced tools. Techniques for examination are discussed separately. (See "Approach to the adult with acute persistent visual loss", section on 'Physical examination'.)

•Visual acuity – Visual acuity is often reduced in RVO, though normal visual acuity does not totally exclude the diagnosis. Visual acuity is generally worse in central retinal vein occlusion (CRVO) and hemiretinal vein occlusion (HRVO) than in branch retinal vein occlusion (BRVO) because of greater retinal ischemia in CRVO and HRVO. Visual acuity in CRVO depends on whether the CRVO is nonischemic (perfused) or ischemic. In one observational study of patients seen within three months of symptom onset, visual acuity was 20/100 or better in most patients (78 percent) with nonischemic CRVO, with 23 percent having 20/20 vision [20]. However, most patients with ischemic CRVO (99 percent) had a visual acuity of 20/200 or worse.

Vision is subjective and highly variable as some patients may have visual symptoms even with 20/20 visual acuity, while others present with 20/100 or worse vision.

•Pupillary function – Assessment for relative afferent pupillary defect should be conducted. An ipsilateral relative afferent pupillary defect is typically present in patients with ischemic CRVO (picture 4). The pupil examination is normal in BRVO.

•Confrontation visual fields – Visual field deficits vary, depending upon the location and density of visual field loss. Poor visual acuity, such as when the patient is only able to perceive hand motions or light perception in ischemic CRVO, may permit only a gross assessment of visual field involvement, and a focal visual field deficit may not be detected. In BRVO, detailed confrontation visual fields with a small test object may detect paracentral scotomas or peripheral defects.

•Extraocular motility – Extraocular motility, evaluated by asking the patient to look in the six cardinal directions of gaze (figure 2), is unaffected in all RVO types.

●Ophthalmologist examination – In addition to the components of the basic examination as above, ophthalmologists evaluate other components of the examination as follows:  

•Intraocular pressure – Intraocular pressure may be measured by a tonopen, applanation device, or other standardized instrument. A slightly lower intraocular pressure in the affected eye than the unaffected eye may be seen in the initial presentation of CRVO, presumably due to ciliary body hyposecretion. Intraocular pressure is unaffected in BRVO. Elevated intraocular pressure may be associated with neovascular glaucoma.

•Slit lamp exam – Anterior segment examination (slit lamp findings) are initially unaffected in RVO. Later in the course (typically within a few months), neovascularization of the iris and anterior chamber angle may occur. Neovascularization of the iris is often first detected in the peripupillary region, but can also develop initially in the anterior chamber angle, particularly in aphakic eyes (eyes without lenses, typically due to cataract surgery). Neovascularization of the iris and anterior chamber angle is best detected prior to pharmacologic pupillary dilation, which puts the peripupillary iris on stretch, making abnormal vessels less visible.

•Dilated fundus exam – Presence of afferent pupillary defect and anterior neovascularization should be evaluated before dilation. Examination findings of the ocular fundus in RVO include retinal hemorrhage, edema, dilated retinal venules, and cotton wool spots throughout the distribution of the affected vein.

-The classic appearance of CRVO has been termed a "blood and thunder" fundus, with dilated and tortuous retinal veins. All four quadrants have intraretinal hemorrhages (picture 1). Cotton wool spots are observed in approximately one-half of patients [21]. Optic nerve edema (papilledema) may be present. The arterioles may be attenuated, indicating generalized arteriosclerotic disease.

-In BRVO, the area of retinal hemorrhage is focal or wedge-shaped, with the apex situated at the offending arteriovenous crossing (picture 5). There may also be venous dilatation radiating from the arteriovenous crossing (image 1).

Clinical diagnosis — A clinical diagnosis can be made based on the characteristic history and ophthalmologic findings described above (see 'When to suspect RVO' above). The diagnosis is often confirmed based on findings on fluorescein angiography (eg, delayed venous filling, staining of affected retinal veins, extravasation of dye from abnormal vessels). (See 'Fluorescein angiography' below.)

Differential diagnosis — The differential diagnosis can be categorized based on the presenting symptom and by the fundoscopic examination findings.

Based on symptoms, the differential diagnosis of sudden, painless, visual loss involving one eye may include (algorithm 1):

●Vitreous hemorrhage – Vitreous hemorrhage can occur in patients with severe diabetic retinopathy who have proliferative disease (growth of abnormal, fragile blood vessels predisposed to bleeding). Visual loss is also typically sudden and painless. However, patients often have a history of poorly controlled or long-standing diabetes and may describe floaters (small, shadowy shapes in the field of vision). On fundus examination, red blood cells and hemorrhage within the vitreous humor are present.

●Retinal detachment – Retinal detachment may occur in patients with proliferative diabetic retinopathy or patients with high myopia. Typically, patients describe floaters, flashes of light, or a dark curtain over a part of the field of vision, which is not typical in RVO. (See "Retinal detachment", section on 'Clinical presentation'.)

●Retinal artery occlusion (central or branch) – Patients with central retinal artery occlusion typically have severe visual loss and can only detect hand motion or count fingers, while those with branch retinal artery occlusion have less severe visual loss. Occasionally, these patients may have episodes of transient monocular vision loss (amaurosis fugax) prior to developing the retinal artery occlusion. Diagnosis and differentiation from RVO is made on fundus examination, where retinal pallor is present, and emboli may be visualized in the vasculature (in retinal artery occlusion). (See "Central and branch retinal artery occlusion", section on 'Acute clinical features'.)

●Ischemic optic neuropathy – Patients with ischemic optic neuropathy often report decrease of vision over hours to days. Some patients may also report a visual field deficit along the horizontal axis (ie, a deficit in the superior or inferior hemisphere of vision) due to the orientation of affected nerve fibers at the optic nerve head. On examination, patients may have a wide range of visual acuity (from 20/20 to no light perception) and an afferent pupillary defect. In contrast to those with RVO, those with optic neuropathy may have reduced color vision (particularly detecting the color red). Further, fundus examination shows optic nerve edema, and sometimes small hemorrhages at the optic nerve head (splinter hemorrhage), but absence of dilated retinal veins or hemorrhages throughout the retina. (See "Nonarteritic anterior ischemic optic neuropathy: Clinical features and diagnosis", section on 'Clinical features'.)

Causes of monocular vision loss are discussed in detail elsewhere. (See "Approach to the adult with acute persistent visual loss" and "Amaurosis fugax (transient monocular or binocular visual loss)".)

Based on fundoscopic examination findings, the differential diagnosis of nontraumatic intraretinal hemorrhages (with or without optic nerve head or macular edema) includes:

●Diabetic retinopathy

●Acute hypertensive retinopathy

●Ocular ischemic syndrome

●Retinal vasculitis

●Radiation retinopathy

●Infectious retinitis, (most commonly viral, and in particular, cytomegalovirus retinitis), which can produce hemorrhages and whitish-gray retinal opacification along the vascular arcades

These conditions can often be suspected based on the patient’s medical history (eg, history of radiation, presence of a systemic infection or autoimmune disorder, severe immunodeficiency such as uncontrolled HIV infection). However, these fundoscopic findings are best detected and further managed by an ophthalmologist.

POSTDIAGNOSTIC EVALUATION

Testing for underlying cardiovascular disease and hypercoagulability — We screen patients for cardiovascular risk factors by obtaining a fasting glucose level or hemoglobin A1C and a fasting lipid panel. Selected patients may require additional evaluation. (See "Overview of primary prevention of cardiovascular disease in adults", section on 'Identifying and addressing key risk factors'.)

In addition, we perform a hypercoagulability workup in patients with a high pretest probability or suspicion for potential hypercoagulability; these primarily include patients with a personal or family history suggestive of a hypercoagulable state and patients under age 50 who do not have strong evidence of arteriosclerotic risk factors. Hypercoagulable testing is discussed in detail elsewhere. Patients with an abnormal hypercoagulable workup are referred to hematology for further evaluation and management. Good communication with the receiving hematology service is also advised as some hematologists prefer to perform the initial workup themselves or in accordance with institutional preference. (See "Evaluating adult patients with established venous thromboembolism for acquired and inherited risk factors", section on 'Hypercoagulable tests'.)

Studies have variable outcomes regarding the potential association between RVO and hypercoagulable markers, and a 2020 meta-analysis did not support routine thrombophilia screening in individuals with RVO, although it acknowledged possible applicability of their findings to young patients without cardiovascular risk factors [13,16,22,23].

Ophthalmologic testing

Fluorescein angiography — Fluorescein angiography is a procedure lasting approximately 10 to 20 minutes in which fluorescein dye is injected into a peripheral vein and a special camera is used to visualize retinal blood flow. In cases where the diagnosis is unclear based on history and examination findings, it is the definitive test to confirm the diagnosis of RVO. Fluorescein angiogram is also used to classify central retinal vein occlusion (CRVO) as ischemic or nonischemic, which determines the optimal treatment. Findings include delayed venous filling, staining of affected retinal veins, and angiographic macular leakage (extravasation of dye from abnormal vessels) in RVOs of recent and longstanding duration.

In the past, angiography was typically performed using traditional cameras with a field of view of 30 to 50 degrees. Newer wide-field (WF) and ultra-widefield (UWF) camera systems show fields of view up to 200 degrees, and are now commonly used for retinal angiography. These WF and UWF systems can allow for better characterization of peripheral ischemia, perfusion deficits, microaneurysms, leakage, retinal neovascularization, vascular remodeling, and other features in a single field of view, without the need for collaging of images from smaller fields of view (image 2).

In longstanding CRVO and branch retinal vein occlusion (BRVO) that have been present for months, fluorescein angiogram also helps document the presence of collateral vessels, which divert blood from the retinal circulation to the choroidal circulation. These collateral vessels are larger in caliber than those of neovascularization and do not leak in the late phases of the angiogram. By contrast, neovascular vessels appear as fine fronds that leak profusely.

Fluorescein angiogram is also used to classify CRVO as ischemic or nonischemic, and quantify the surface area of nonperfusion (which affects the risk of neovascularization), to determine the optimal treatment. The Central Retinal Vein Occlusion Study Group established a perfusion classification scheme, based on disc area, that is now commonly used [21]. A disc area represents the surface area of the optic nerve head. In this scheme, cases with <10 disc areas of capillary nonperfusion are classified as "perfused CRVO," and cases with ≥10 disc areas of capillary nonperfusion are classified as "nonperfused CRVO." Cases of CRVO where the extent of capillary nonperfusion cannot be determined due to extensive intraretinal hemorrhage are classified as "indeterminant" [9]. The area of involvement on angiogram, and the presence of neovascularization or macular edema, determines whether laser photocoagulation therapy or intraocular injections of vascular endothelial growth factor (VEGF) inhibitors is indicated. (See "Retinal vein occlusion: Treatment", section on 'Retinal laser photocoagulation'.)

BRVO is also classified into perfused (non-ischemic) or nonperfused (ischemic) on fluorescein angiography. Ischemic BRVO is defined as >5 disc diameters of nonperfusion on fluorescein angiography [24]. The amount and location of capillary nonperfusion in BRVOs is helpful to predict visual acuity and neovascularization risk.

Optical coherence tomography — Macular optical coherence tomography (OCT) allows high-resolution cross-sectional imaging of the retina [25]. Its main use in RVO is in quantifying retinal thickening from intraretinal fluid in cases of macular edema (image 3). OCT can then be used on follow-up visits to assess the progression of RVO or response to treatment.

NATURAL HISTORY AND COMPLICATIONS — 

The natural history of visual acuity after RVO varies based on the size and type of occlusion. Complications of RVO can include macular edema, neovascularization, and, less commonly, vitreous hemorrhage. In addition, as RVO may be a marker of underlying cardiovascular disease, it has been associated with future stroke, myocardial infarction, and cardiovascular mortality in observational studies [26-28].

Effects on visual acuity — Whether visual loss progresses depends largely on the type and location of the occlusion as well as any development of macular edema [29,30].

●CRVO – Patients with CRVO have generally worse outcomes compared with BRVO, with final visual acuity dependent upon visual acuity at presentation. Further, patients with ischemic CRVO, compared with nonischemic CRVO, are at higher risk for poor visual acuity at initial presentation and over the long term [20]. The Central Retinal Vein Occlusion Study followed 725 patients with CRVO over three years [30]. Two-thirds of patients who presented with visual acuity better than 20/40 maintained visual acuity in the same range, and only 10 percent had worsening of visual acuity to less than 20/200. Among patients who presented with visual acuity 20/50 to 20/200, nearly one-half maintained visual acuity in the same range and one-third progressed to a visual acuity of less than 20/200. In patients who presented with initial visual acuity of less than 20/200, only 20 percent of patients had some improvement in vision.

●BRVO – Patients with BRVO without macular edema are commonly asymptomatic and maintain good vision. Patients with macular edema may experience spontaneous vision improvement in the first few months after onset of symptoms due to self-limiting improvement or resolution of the edema. However, after three months, the likelihood of spontaneous improvement in visual acuity diminishes. In the Branch Vein Occlusion Study, three-year visual acuity outcomes in untreated eyes with BRVO-associated macular edema and visual acuity of 20/40 or worse at three months were as follows: 34 percent with visual acuity of 20/40 or better, 23 percent with visual acuity of 20/200 or worse, and an average visual acuity of 20/70 [24].

Ocular neovascularization — Neovascularization of the iris, the anterior chamber angle, and retina are common complications of CRVO and BRVO, although these complications occur more commonly in CRVO. In the Central Retinal Vein Occlusion Study, neovascularization of the iris and/or anterior chamber angle developed in 16 percent of patients [30]. The strongest predictors of neovascularization of the iris and/or anterior chamber angle were visual acuity at diagnosis and the size of nonperfused area on fluorescein angiogram. For eyes initially categorized as nonperfused (ischemic) or indeterminate, 35 percent developed neovascularization of the iris and/or anterior chamber angle, compared with 10 percent of those initially categorized as perfused [30].

Neovascularization can lead to glaucoma or hemorrhage.

●Neovascular glaucoma – Neovascularization of the iris and neovascularization of the anterior chamber angle are considered harbingers of neovascular glaucoma. Neovascular glaucoma has been called "90-day glaucoma" because of its common onset within a few months of onset of ischemic CRVO. These patients may present with a red, painful eye secondary to elevated intraocular pressure, in addition to decreased vision. Development of neovascular glaucoma may result in significant long-term ocular morbidity, such as chronic pain, ocular redness, unremitting intraocular pressure elevation, and profound visual loss that is often unresponsive to topical glaucoma eye drops or surgery.

●Vitreous hemorrhage – Neovascularization of the retina can lead to vitreous hemorrhage, which can cause decreased visual acuity and visual disturbances, such as severe floaters, that obscure vision. Long term, retinal scarring may result in tractional retinal detachment. (See "Retinal detachment" and "Approach to the adult with acute persistent visual loss", section on 'Vitreous hemorrhage'.)

FOLLOW-UP — 

Patients with RVO are typically followed up by an ophthalmologist. During follow-up, visual acuity is documented at each visit (frequency of visits depending on severity of RVO) to assess progression or regression (see "Retinal vein occlusion: Treatment").

In eyes with severe visual loss and suspected nonperfused central retinal vein occlusion (CRVO), ophthalmologists also perform:

●A periodic (every four to six week) examination of the iris and retina during the first six to eight months of diagnosis to detect neovascularization of these structures. Examination of the iris is best done before eye dilation.

●Gonioscopy (using a special lens to visualize the anterior chamber angle of the eye) to detect neovascularization at the anterior chamber angle, which is associated with increased intraocular pressure.

●Dilated eye examination to assess for retinal neovascularization and macular edema.

SUMMARY AND RECOMMENDATIONS

●Epidemiology – Retinal vein occlusion (RVO) is an important cause of vision loss worldwide. Risk factors in descending order of likelihood include older age, hypertension, diabetes, cardiovascular disease, smoking, and hypercoagulable states. (See 'Epidemiology' above.)

●Classification and pathophysiology – The classification of RVO is based on the site of retinal vein involvement:

•Central retinal vein occlusion (CRVO) occurs when a proximal retinal vein is occluded by thrombus, leading to involvement of the entire retina (picture 1). CRVO is further classified as ischemic or nonischemic (perfused), depending on the degree of retinal venous obstruction and perfusion of the retina.

•Hemiretinal vein occlusion (HRVO) is the least common of these entities and describes blockage of a vein that drains the superior or inferior hemiretina, leading to involvement of one-half of the retina (picture 2). The pathophysiology is similar to that of CRVO. (See 'Classification and pathophysiology' above.)

•Branch retinal vein occlusion (BRVO) is the most common of these entities and occurs when a distal retinal vein is occluded, leading to hemorrhage along the distribution of a small vessel of the retina (picture 3). The pathophysiology is hypothesized to be due to compression of retinal veins by inflexible, atherosclerotic overlying arterioles at arteriovenous crossings. (See 'Classification and pathophysiology' above.)

●Symptoms – Patients with RVO may be asymptomatic or present with unilateral painless vision loss or visual field deficits. Patients with CRVO usually report reduced visual acuity. Some patients with BRVO may be asymptomatic, with abnormalities limited to those detected on routine eye examination, while others present with visual field defects and reduced visual acuity, due to macular edema. Because the retina has no trigeminal innervation, patients do not report ocular pain. (See 'Symptoms' above.)

●Eye examination findings – Basic eye examination reveals either normal or variably decreased visual acuity. Visual field deficits are possible. Extraocular motility and pupil reactivity are typically not affected. An afferent pupillary defect may be present in ischemic CRVO.

Fundoscopic findings include retinal hemorrhage, edema, dilated retinal venules, and cotton wool spots throughout the distribution of the affected vein (picture 5 and image 1). (See 'Eye examination and findings' above.)

●Diagnosis – The diagnosis of RVO can be made clinically based on a characteristic history and findings on ophthalmologic examination. Important components of the ophthalmic examination include visual acuity and dilated fundus examination evaluating for hemorrhage, edema, and dilation of the retinal veins. Fluorescein angiogram is performed for confirmation of diagnosis, prognostication, and to assess the need for treatment. (See 'Evaluation and diagnosis' above and 'Ophthalmologic testing' above.)

●Identifying underlying risk factors – We screen patients for cardiovascular risk factors by obtaining a fasting glucose or hemoglobin A1C and a fasting lipid panel. In addition, we perform a hypercoagulable workup in patients with a personal or family history suggesting a hypercoagulable state, and in patients under age 50 who do not have strong evidence of arteriosclerotic risk factors. (See 'Testing for underlying cardiovascular disease and hypercoagulability' above.)

●Complications – The natural history of visual acuity after RVO varies according to the size and type of occlusion. Complications of RVO can include macular edema and neovascularization. Neovascularization of the iris and anterior chamber angle may cause neovascular glaucoma, while neovascularization of the retina can cause vitreous hemorrhage. (See 'Natural history and complications' above.)

●Follow-up – In eyes with severe visual loss and suspected nonperfused CRVO, ophthalmologists perform a periodic (every four to six weeks) examination of the iris and retina during the first six to eight months of diagnosis to detect neovascularization of these structures. Examination of the iris is best done before eye dilation. Gonioscopy is performed to detect neovascularization of the anterior chamber angle, which is associated with increased intraocular pressure. Dilated eye examination should also be performed in conjunction for assessment of retinal neovascularization and macular edema. (See 'Follow-up' above.)

ACKNOWLEDGMENT — 

The UpToDate editorial staff acknowledges Douglas Covert, MD, MPH, who contributed to an earlier version of this topic review.