Central retinal vein occlusion (CRVO) is a common retinal vascular disorder. Clinically, CRVO presents with variable visual loss; the fundus may show retinal hemorrhages, dilated tortuous retinal veins, cotton-wool spots, macular edema, and optic disc edema. Note the images below.
Recent onset central retinal vein occlusion, showing extensive hemorrhages in the posterior pole and giving the "blood and thunder appearance."
Peripheral fundus view of the same patient as in the previous image, showing hemorrhages extending all over the fundus.
Fluorescein angiograph of same patient as in previous images, showing hypofluorescence due to blockage from hemorrhages in the retina. It is not usefu....
Fundus picture of the same patient as in previous images, showing resolving neovascularization of the disc and panretinal photocoagulation scars.
Fluorescein angiogram of the same patient as in the previous images, taken more than 1 year later, showing persistent cystoid macular edema with good ....
In view of the devastating complications associated with the severe form of CRVO, a number of classifications were described in the literature. All of these classifications take into account the area of retinal capillary nonperfusion and the development of neovascular complications.[1, 2, 3, 4, 5]
Broadly, CRVO can be divided into 2 clinical types, ischemic and nonischemic. In addition, a number of patients may have an intermediate in presentation with variable clinical course. On initial presentation, it may be difficult to classify a given patient into either category, since CRVO may change with time.
A number of clinical and ancillary investigative factors are taken into account for classifying CRVO, including vision at presentation, presence or absence of relative afferent pupillary defect, extent of retinal hemorrhages, cotton-wool spots, extent of retinal perfusion by fluorescein angiography, and electroretinographic changes.
Nonischemic CRVO is the milder form of the disease. It may present with good vision, few retinal hemorrhages and cotton-wool spots, no relative afferent pupillary defect, and good perfusion to the retina. Nonischemic CRVO may resolve fully with good visual outcome or may progress to the ischemic type. Note the images below.
Patient with nonischemic central retinal vein occlusion presented with dilated, tortuous veins and superficial hemorrhages.
Fundus picture of the same patient as in previous image, showing resolved hemorrhages and pigmentary changes in the macula several months later.
Ischemic CRVO is the severe form of the disease. CRVO may present initially as the ischemic type, or it may progress from nonischemic. Usually, ischemic CRVO presents with severe visual loss, extensive retinal hemorrhages and cotton-wool spots, presence of relative afferent pupillary defect, poor perfusion to retina, and presence of severe electroretinographic changes. In addition, patients may end up with neovascular glaucoma and a painful blind eye.
The exact pathogenesis of the thrombotic occlusion of the central retinal vein is not known. Various local and systemic factors play a role in the pathological closure of the central retinal vein.[3, 6, 7]
The central retinal artery and vein share a common adventitial sheath as they exit the optic nerve head and pass through a narrow opening in the lamina cribrosa. Because of this narrow entry in the lamina cribrosa, the vessels are in a tight compartment with limited space for displacement. This anatomical position predisposes to thrombus formation in the central retinal vein by various factors, including slowing of the blood stream, changes in the vessel wall, and changes in the blood.
Arteriosclerotic changes in the central retinal artery transform the artery into a rigid structure and impinge upon the pliable central retinal vein, causing hemodynamic disturbances, endothelial damage, and thrombus formation. This mechanism explains the fact that there will be an associated arterial disease with CRVO. However, this association has not been proven consistently, and various authors disagree on this fact.
Thrombotic occlusion of the central retinal vein can occur as a result of various pathologic insults, including compression of the vein (mechanical pressure due to structural changes in lamina cribrosa, eg, glaucomatous cupping, inflammatory swelling in optic nerve, orbital disorders); hemodynamic disturbances (associated with hyperdynamic or sluggish circulation); vessel wall changes (eg, vasculitis); and changes in the blood (eg, deficiency of thrombolytic factors, increase in clotting factors).
Occlusion of the central retinal vein leads to the backup of the blood in the retinal venous system and increased resistance to venous blood flow. This increased resistance causes stagnation of the blood and ischemic damage to the retina. It has been postulated that ischemic damage to the retina stimulates increased production of vascular endothelial growth factor (VEGF) in the vitreous cavity. Increased levels of VEGF stimulate neovascularization of the posterior and anterior segment (responsible for secondary complications due to CRVO). Also, it has been shown that VEGF causes capillary leakage leading to macular edema (which is the leading cause of visual loss in both ischemic CRVO and nonischemic CRVO).
The prognosis of CRVO depends upon the reestablishment of patency of the venous system by recanalization, dissolution of clot, or formation of optociliary shunt vessels.
CRVO and branch retinal vein occlusion constitute the second most common retinal vascular disorder. The nonischemic type is more common than the ischemic type.
In a recent publication, the Beaver Dam Eye Study Group reported the 15-year cumulative incidence of CRVO to be 0.5%.
A large population-based study in Israel reported a 4-year incidence of retinal vein occlusion of 2.14 cases per 1000 of general population older than 40 years and 5.36 cases per 1000 of general population older than 64 years.
In Australia, the prevalence of vein occlusion ranges from 0.7% in patients aged 49-60 years to 4.6% in patients older than 80 years.
CRVO is not associated directly with increased mortality.
Nonischemic CRVO may resolve completely without any complications in about 10% of cases. In about 50% of patients, vision may be 20/200 or worse. One third of patients may progress to the ischemic type, commonly in the first 6-12 months after presentation.
In more than 90% of patients with ischemic CRVO, final visual acuity may be 20/200 or worse. Anterior segment neovascularization with associated neovascular glaucoma develops in more than 60% of cases. This can happen within a few weeks and up to 1-2 years afterward.
It has been reported that the fellow eye may develop retinal vein occlusion in about 7% of cases within 2 years. In another report, the 4-year risk of developing second venous occlusion is 2.5% in the same eye and 11.9% in the fellow eye. Neovascular glaucoma may result in a painful blind eye.
CRVO does not have any particular racial preference.
CRVO occurs slightly more frequently in males than in females.
More than 90% of CRVO occurs in patients older than 50 years, but it has been reported in all age groups.
A direct review of systems toward the various systemic and local factors predisposing the CRVO is indicated.
Significant history includes the following:
Ocular symptoms at initial presentation are as follows:
Ocular symptoms in later stages are as follows:
Patients should undergo a complete eye examination, including visual acuity, pupillary reactions, slit lamp examination of the anterior and posterior segments, undilated examination of the iris, gonioscopy, fundus examination with indirect ophthalmoscope, and fundus contact lens. Note the following:
Scattered retinal hemorrhages in a patient with central retinal vein occlusion.
Fundus of a patient with nonischemic central retinal vein occlusion, showing few scattered peripheral fundus hemorrhages.
Recent onset central retinal vein occlusion, showing extensive hemorrhages in the posterior pole and giving the "blood and thunder appearance."
Central retinal vein occlusion showing significant disc edema with dilated tortuous veins and scattered retinal hemorrhages.
Fluorescein angiogram of the same patient in as in previous image, showing leakage from disc, staining of retinal veins.
Fundus picture of a well-compensated, old central retinal vein occlusion showing optociliary shunt vessels.
Red-free photo of the same patient as in the previous image, showing prominent optociliary shunt vessels.
Central retinal vein obstruction has been associated with various systemic pathological conditions, although the exact cause and effect relationship has not been proven.
Some of the conditions in which CRVO has been associated include the following:
The Eye Disease Case-Control Study Group reported that the risk of CRVO is decreased in men with increasing levels of physical activity and increasing levels of alcohol consumption. The same study group reported a decreased risk of CRVO with the use of postmenopausal estrogens and an increased risk with higher erythrocyte sedimentation rates in women.
No laboratory studies are routinely indicated in the diagnosis of central retinal vein occlusion (CRVO). In older patients, laboratory testing should be directed toward identifying systemic vascular problems. In young patients, laboratory testing may be tailored depending upon individual findings, to include the following:
Color Doppler imaging is a noninvasive quantitative method of assessing the retrobulbar circulation. Detection of low venous velocities has been used to predict the onset of iris neovascularization. At present, this is performed as an investigational procedure in large facilities.
Optical coherence tomography (OCT) scanning is a noninvasive, noncontact, transpupillary imaging technology that can image retinal structures in vivo with a resolution of 10-17 µm. OCT quantitatively measures the retina in micrometers in situ and in real time. OCT can detect even subtle macular edema in the presence of significant hemorrhages, which is not evident by fluorescein angiography because of blockage from hemorrhage. OCT is useful in quantitatively monitoring the development of macular edema and resolution with treatment.[13, 14]
Fluorescein angiography is the most useful test for the evaluation of retinal capillary nonperfusion, posterior segment neovascularization, and macular edema. Note the images below.
Fluorescein angiogram of a patient with nonischemic central retinal vein occlusion, showing staining of dilated tortuous veins with leakage into macul....
Fluorescein angiogram of the same patient as in previous image, showing perifoveal capillary leakage in a cystoid pattern in late phases of angiogram.....
Late phase of fluorescein angiograph of the same patient as in previous image, showing cystoid pattern of leakage from perifoveal dilated leaking capi....
Fluorescein angiography is one of the tests used in the classification of CRVO. Areas of capillary nonperfusion are visualized as hypofluorescence, but hemorrhages can block fluorescence and give a similar picture. Therefore, in the early stages of the disease process, due to extensive hemorrhages, fluorescein angiography gives little information regarding the perfusion status of the retina. Once the hemorrhages clear, areas of capillary nonperfusion can be detected as hypofluorescence in the fluorescein angiography.
Various studies have reported different criteria for defining ischemic CRVO versus nonischemic CRVO based on the extent of capillary nonperfusion of the retina. The amount of retinal nonperfusion ranges from 10-30 disc areas.
In addition, fluorescein angiography may show delayed arteriovenous transit, staining along the retinal veins, microaneurysms, arteriovenous collaterals, NVD, NVE, and dilated optic nerve head capillaries.
In a nonischemic central retinal vein obstruction, angiography may show minimal or absent retinal capillary nonperfusion, staining along the retinal veins, microaneurysms, and dilated optic nerve head capillaries. Resolved CRVO may be completely normal.
Macular edema may be detected as leakage from perifoveal capillaries (depicted in the image below), leakage from microaneurysms, or diffuse leakage on fluorescein angiography. If extensive edema is present, fluorescein angiography may show pooling of dye in large cystoid spaces. In addition, capillary nonperfusion around the fovea may indicate macular ischemia. If macular edema persists, pigmentary changes become evident.
Arteriovenous phase of fluorescein angiograph showing perifoveal capillary leakage in a patient with nonischemic central retinal vein occlusion.
Electroretinography (ERG) is another useful test to evaluate the functional status of the retina and to classify CRVO.[13, 15, 16] In ERG waveform, b-wave and a-wave are produced by the inner retina and the outer retina, respectively. In central retinal vein obstruction, perfusion of the inner retina is affected, so that the amplitude of the b-wave is decreased relative to the a-wave; the b-to-a ratio has been shown to be reduced. Some studies indicate that a b-to-a ratio of less than 1 suggests an ischemic central retinal vein obstruction.
Not many histopathologic reports exist in the literature. A report of histologic sections of 29 eyes with central retinal vein obstruction showed a fresh or recanalized thrombus at or just posterior to the lamina cribrosa. Within the thrombi, a mild lymphocytic infiltration with prominent endothelial cells was seen. Loss of the inner retinal layers consistent with inner retinal ischemia also was seen.
No known effective medical treatment is available for either the prevention of or the treatment of central retinal vein occlusion (CRVO). Identifying and treating any systemic medical problems to reduce further complications is important. Because the exact pathogenesis of the CRVO is not known, various medical modalities of treatment have been advocated by multiple authors with varying success in preventing complications and in preserving vision.
Advocated treatments are as follows:
In patients with macular edema, injection of triamcinolone (0.1 mL/4 mg) into the vitreous cavity through pars plana has been shown to be effective not only in resolving the edema but also in corresponding improvement in vision.
Even though the exact mechanism of action of intravitreal injections of corticosteroids is not known, the triamcinolone crystals in the vitreous cavity probably reduce VEGF concentrations in the vitreous cavity. This leads to a reduction in capillary permeability and macular edema. The main drawback of an injection of triamcinolone was posttreatment recurrences of macular edema, requiring repeat triamcinolone injections, typically every 3-6 months.
In addition, significant complications reported due to the injection of triamcinolone include cataract, glaucoma, retinal detachment, vitreous hemorrhage, and endophthalmitis.
Because most of the data available for the use of triamcinolone injection is from multiple short-term follow-up studies, a large controlled, randomized clinical trial called the SCORE (Standard Care vs Corticosteroid for Retinal Vein Occlusion) Study is now underway in about 90 centers throughout the United States. This study is funded by the National Eye Institute (NEI) to evaluate the use of intravitreal triamcinolone for macular edema in about 1,200 patients with CRVO or branch retinal vein occlusion (BRVO). All patients are being randomized to either 1 mg or 4 mg of triamcinolone versus standard care therapy (eg, observation in CRVO, laser photocoagulation in BRVO). Patients will be followed for up to 3 years to measure long-term treatment efficacy and safety; reinjections (if needed) will be performed beginning at 4 months after the initial therapy.
Based on the results of the SCORE-CRVO trial, intravitreal triamcinolone using a 1-mg dose and retreatment as needed should be considered for up to 1 year and possibly 2 years in patients with vision loss associated with macular edema secondary to CRVO. Intravitreal triamcinolone in both a 1-mg and 4-mg dose led to better visual acuity outcomes over 12 months than the untreated natural history of macular edema secondary to perfused CRVO. Owing to fewer adverse effects with the 1-mg dose, it is preferred over the 4-mg dose.
In patients with macular edema, injection of bevacizumab (0.05 mL/1.25 mg) into the vitreous cavity through pars plana has been shown to be effective not only in resolving the edema but also in corresponding improvement in vision. Injections of bevacizumab given every 6 weeks for 6 months improve visual acuity and significantly reduce edema compared with sham.
Also, in patients with neovascular glaucoma, a similar dose has shown significantly decreased angle neovascularization and improved intraocular pressure control, both medically and surgically.
Even though the exact mechanism of action of intravitreal injections of bevacizumab is not known, bevacizumab probably reduces VEGF concentrations in the vitreous cavity. This leads to a reduction in capillary permeability and macular edema. The main drawback of intravitreal injections is post treatment recurrences of macular edema, requiring repeat injections. The FDA has warned that the need to repackage bevacizumab from the available size vial for IV use into smaller doses for intravitreal injections increases risk for transmission of infection if improper aseptic technique occurs. Reports of serious eye infections have been reported regarding this repackaging into preservative-free single use vials. Bevacizumab is not commercially available as an intravitreal injection.
In addition, significant complications reported due to the injection of bevacizumab include cataract, glaucoma, retinal detachment, vitreous hemorrhage, and endophthalmitis.
Significant complications were reported with high doses of bevacizumab given intravenously for the treatment of cancer. There have been no significant reports of these complications in the available small studies.
Vascular endothelial growth factor (VEGF) expression is upregulated by hypoxia and was noted to be elevated in the ocular fluids of patients with CRVO. One of the potent effects of VEGF is to increase vascular permeability in the macula leading to visually significant macular edema.
Ranibizumab is a humanized, affinity-matured VEGF antibody fragment that binds to and neutralizes all isoforms of VEGF. Ranibizumab showed improved visual outcomes in patients with neovascular age-related vascular degeneration due to its anti-VEGF activity. The role of ranibizumab in the management of CRVO was reported in multiple studies. Intraocular injections of 0.3 mg or 0.5 mg ranibizumab provided rapid improvement in 6-month visual acuity and macular edema following CRVO, with low rates of ocular and nonocular safety events.[30, 31] Six months of monthly treatment with ranibizumab in patients with macular edema secondary to branch or central RVO resulted in greater improvements in vision-related function compared with sham treatment, even when most patients presented with RVOs in the worse-seeing eye. Ranibizumab was approved for treatment of macular edema following retinal vein occlusion in June 2010.
Aflibercept was approved for macular edema following CRVO in September 2012. Approval was based on 2 randomized, multicenter, double-blind, placebo-controlled trials (COPERNICUS and GALILEO) in 358 patients. In both studies, patients were randomly assigned in a 3:2 ratio to either 2 mg aflibercept administered every 4 weeks or placebo injections. The primary efficacy endpoint was the proportion of patients who gained at least 15 letters in best corrected visual acuity (BCVA) as measured by Early Treatment Diabetic Retinopathy Study (ETDRS) eye charts at week 24 compared to baseline. The aflibercept injection demonstrated a statistically significant difference in the proportion of patients who gained ≥15 letters from baseline at week 24 compared with placebo (p < 0.01) in each study.[49, 50]
Dexamethasone is a potent, water-soluble corticosteroid that can be delivered to the vitreous cavity by the dexamethasone intravitreal implant (DEX implant; OZURDEX, Allergan; Irvine, Calif). A dextramethasone implant is composed of a biodegradable copolymer of lactic acid and glycolic acid containing micronized dexamethasone. The drug-copolymer complex gradually releases the total dose of dexamethasone over a series of months after insertion into the eye through a small pars plana puncture using a customized applicator system.
A 6-month study evaluated the safety and efficacy of dextramethasone implant 0.35 mg and 0.7 mg compared with a sham procedure in eyes with vision loss due to macular edema associated with BRVO and CRVO. In conclusion, the results of the study demonstrated that the dextramethasone implant reduced the risk of further vision loss and increased the chance of improvement in visual acuity in eyes with CRVO.
The percentage of eyes with a greater than or equal to 15-letter improvement in BCVA was significantly higher in both dextramethasone implant groups compared with sham at days 30 to 90 (P < .001). The results of this study further demonstrate that when these eyes were left untreated, a significant percentage will either fail to improve or will experience further loss of visual acuity. The dexamethasone implant was well tolerated, producing generally transient, moderate, and readily managed increases in IOP in less than 16% of eyes. Overall, this study suggests that the DEX implant could be a valuable new treatment option for eyes with visual loss due to CRVO.
Laser photocoagulation is the known treatment of choice in the treatment of various complications associated with retinal vascular diseases (eg, diabetic retinopathy, branch retinal vein occlusion). Panretinal photocoagulation (PRP) has been used in the treatment of neovascular complications of CRVO for a long time. However, no definite guidelines exist regarding exact indication and timing of PRP. A National Eye Institute (NEI) sponsored multicenter prospective study, the Central Vein Occlusion Study (CVOS), provided guidelines for the treatment and follow-up care of patients with CRVO.[1, 10, 32, 33, 34]
CVOS evaluated the efficacy of prophylactic PRP in eyes with 10 or more disc areas of retinal capillary nonperfusion, confirmed by fluorescein angiography, in preventing development of 2 clock hours of iris neovascularization or any angle neovascularization or whether it is more appropriate to apply PRP only when iris neovascularization or any angle neovascularization occurs. CVOS concluded that prophylactic PRP did not prevent the development of iris neovascularization and recommended to wait for the development of early iris neovascularization and then apply PRP.
Argon green laser usually is used. Laser parameters should be about 500-µm size, 0.1-0.2 second duration, and power should be sufficient to give medium white burns. Laser spots are applied around the posterior pole, extending anterior to equator. They should be about 1 burn apart and total 1200-2500 spots.
If ocular media is hazy for laser to be applied, cryoablation of the peripheral fundus is performed. About 16-32 transscleral cryo spots are applied from ora serrata posteriorly.
CVOS evaluated the efficacy of macular grid photocoagulation in preserving or improving central visual acuity in eyes with macular edema due to central vein occlusion (CVO) and best-corrected visual acuity of 20/50 or poorer. Macular grid photocoagulation was effective in reducing angiographic evidence of macular edema, but it did not improve visual acuity in eyes with reduced vision due to macular edema from CVO. At present, the results of this study do not support a recommendation for macular grid photocoagulation for macular edema.
Chorioretinal venous anastomosis[35, 36, 37, 38, 39] is performed by creating an anastomosis to bypass the site of venous occlusion in the optic disc. In this procedure, retinal veins are punctured, either using laser or by surgery, through the retinal pigment epithelium and the Bruch membrane into the choroid, thereby developing anastomotic channels into the choroid.
Chorioretinal venous anastomosis reduces macular edema and may improve vision in nonischemic CRVO. The success rate is low, and the complication rate can be quite high, including vitreous hemorrhages and choroidal neovascularization at the anastomosis site.
The exact indication and timing of the procedure has not been clearly studied.
Radial optic neurotomy (RON)[40, 41, 42, 43, 44, 45] is a new surgical technique in which a microvitreoretinal blade is used during pars plana vitrectomy to relax the scleral ring around the optic nerve. The central retinal artery and vein passes through the narrow openings of the cribriform plate in the optic disc.
Promoters of this technique suggest that CRVO may be due to the compression of the central retinal vein at this location creating a compartment syndrome. If this procedure is successful, it decompresses the closed compartment and leads to an improvement in venous outflow and a reduction of macular edema.
In one recent study, RON resulted in clinically relevant improvements on a long-term basis. Patients with nonischemic CRVO may respond more favorably than patients with ischemic CRVO.
In another study, significant improvements were observed in the b-to-a ratio of the standard combined ERG after surgery in eyes with CRVO.
The benefits from surgery have not been clearly documented. One study, looking into the biomechanical effect of RON, found negligible change in the space around the central retinal vein; RON is unlikely to be a procedure that could mechanically ameliorate the clinical sequelae of a central vein occlusion. The improvement of retinal function is most likely due to improved oxygenation of the retina caused by vitrectomy and not by RON.
In addition to the regular complications of vitrectomy, RON can result in significant hemorrhage and neovascularization at the incision site.
No consensus currently exists among various researchers regarding the exact criteria for the use of RON.
A vitrectomy is a technique in which the vitreous is surgically removed along with removal of the posterior hyaloid.
Some studies have shown that a vitrectomy may be beneficial for macular edema due to CRVO. One theory is that a vitrectomy may relieve traction on the macula and, thus, reduce macular edema. According to another hypothesis, removing the vitreous will also remove cytokines and VEGF associated with a venous occlusive event; thus, the stimulus for macular edema will be reduced.
At the present time, no convincing evidence indicates that a vitrectomy is the best approach.
A general ophthalmologist should consult a retinal specialist for management of CRVO complications. Other consults include an internist for proper evaluation and management of any systemic medical problems. If patients develop neovascular glaucoma, a glaucoma specialist should be consulted.
Diet should be tailored to systemic medical problems.
No restrictions usually exist. If patients develop vitreous hemorrhage, they are advised to avoid strenuous activities, sleep with few pillows, and avoid bending and lifting heavy weights.
VEGF-A has been shown to cause neovascularization and leakage in models of ocular angiogenesis and vascular occlusion, and is thought to contribute to the progression of macular edema following RVO. Antibodies that bind to VEGF-A receptors prevent the interaction of VEGF-A with its receptors (VEGFRl and VEOFR2) on the surface of endothelial cells, thus reduce endothelial cell proliferation, vascular leakage, and new blood vessel formation.
Clinical Context: VEGF antibody. Indicated for macular edema following retinal vein occlusion.
Clinical Context: VEGF antibody. Indicated for macular edema following central retinal vein occlusion.
These agents bind to VEGF-A receptors to arrest macular edema and improve visual acuity associated with CVRO.
Since neovascular complications and development of second venous occlusions can develop after central retinal vein occlusion (CRVO), all of these patients need follow-up care for long periods of time.
CVOS recommended careful observation with frequent follow-up examinations in the early months for detection of iris neovascularization and prompt treatment.
Patients with poor initial visual acuity should be monitored every month during the first few months and spaced thereafter, depending on the course of the disease. These criteria apply more for patients with ischemic CRVO than with patients with nonischemic CRVO.
With any associated complications, follow-up care should be individualized.
Optimal control of associated systemic diseases may reduce the incidence of similar occlusions in the fellow eye.
Even though controversial, good control of intraocular pressure in patients known to have glaucoma may prevent CRVO.
Ocular neovascularization is a potential complication. Anterior segment neovascularization can lead to neovascular glaucoma. Posterior segment neovascularization can lead to vitreous hemorrhage.
Macular edema is another potential complication.[19, 34, 47] Macular edema is the common cause of decreased vision in CRVO, more so in the nonischemic type. It may resolve with good visual return. The patient may develop permanent degenerative changes with poor visual prognosis and may develop cystoid macular edema leading to lamellar or full-thickness macular hole.
Other potential complications include cellophane maculopathy and macular pucker, as well as optic atrophy.
For nonischemic CRVO, complete recovery with good visual recovery occurs only in about 10% of cases. Fifty percent of patients will have 20/200 or worse vision. About one third of patients convert to ischemic CRVO. CVOS noted that, of 547 eyes initially diagnosed to have nonischemic central retinal vein obstructions, 185 (34%) progressed to become ischemic central retinal vein obstructions within 3 years; 15% converted within the first 4 months.
For ischemic CRVO, more than 90% of patients will have 20/200 or worse vision. About 60% of patients develop ocular neovascularization with associated complications. About 10% of patients can develop CRVO or other type of vein occlusions within either the same eye or the contralateral eye within 2 years.