Central retinal vein occlusion (CRVO), a member of the group of retinal vascular diseases, is a sight-threatening condition that needs to be correctly diagnosed and treated to diminish its consequences, leading to painful blindness if neovascular glaucoma (NVG) develops. CRVO occurs predominantly in adults 65 years old and over.
The prevalence does not differ by gender, and it is predominantly unilateral. Some described systemic risk factors are end-organ damage from hypertension or diabetes, a hypercoagulable state, and a diagnosis of stroke or obstructive sleep apnea. The most described ocular risk factor is glaucoma. Patients with CRVO also show an increased (almost two-fold) incidence in cerebrovascular accidents than age and sex-matched controls in a US population.
Fortunately, this is a relatively easy condition to diagnose based mostly on its clinical features. CRVO commonly presents as a sudden and painless loss of vision. Occasionally, the vision loss occurs gradually, mostly happens at night time in the recumbent position, probably by low blood pressure and/or high central venous pressure.
The typical fundoscopic features appear in all the four quadrants of the fundus: venous tortuosity and dilation, retinal hemorrhages (scattered superficial and deep), and cotton wool spots. Macular edema and optic disc swelling are also present. All these features are present in varying degrees depending on the severity of the occlusion.
Long-standing CRVO is suspected if blocked or enclosed retinal veins are observed. Also, if vascular anastomosis is detected at the optic disc is observed. Also known as optociliary collaterals, blood vessels made new blood routes (neovascularization) to the choroid. The choroid is the part of the eye responsible for the vascular support of the outer retina.
Two types of central retinal vein occlusion
There are two clinical types of central retinal vein occlusion: Ischemic – caused by an inadequate blood supply, and Non-ischemic – not marked by or resulting from ischemia. Non-ischemic is the most common type, accounting for about 75% of CRVO cases. Patients with Non-Ischemic CRVO experience mild to moderate acuity loss, typically 20/200 or better.
They may also have and an absent or mild Relative Afferent Pupillary Defect (RAPD). This defect can be diagnosed when your ophthalmologist alternately shines a light into your left and right eyes. Normally both pupils will constrict equally no matter which eye your retinal specialist shines the light at. A CRVO affected eye will produce less constriction of the pupil than light shone in the unaffected eye.
Patients with Ischemic CRVO may have severe visual loss (20/200 or worse), a marked different defect of the pupils, and poor blood flow to the retina. An Electroretinography (ERG) eye test may detect severe electrical responses of various cell types in the retina. Progression from non-ischemic to ischemic CRVO happens in 15% of cases within four months and 34% within three years.
Your retinal specialist will perform a general clinical assessment to diagnose signs of central retinal vein occlusion that may include:
- Complete blood count
- Renal function (serum levels of urea and creatinine)
- Fasting serum lipids
- Fasting serum levels of glucose and glycated hemoglobin
Further advanced testing may be done with:
Fluorescein Angiography (FA): Your ophthalmologist injects (painlessly) a fluorescent dye into you’re your bloodstream that highlights your retina’s blood vessels. With a special camera, any problems with the circulation of blood in the retina can be observed.
Optical Coherence Tomography (OCT): OCT is a non-invasive imaging test that uses light waves to take cross-section pictures of your retina. OCT allows the retinal specialist to view each layer of your retina and map and measure their thickness.
Electroretinogram (ERG): An ERG measures the retina’s electrical activity in response to a light stimulus. ERG is an important diagnostic tool for patients with central retinal vein occlusion as it measures the function of rod and cone photoreceptors.
Differing between ischemic and non-ischemic CRVO
Differential diagnosis of CRVO is not a difficult task. Other pathologies such as diabetic retinopathy, hypertensive retinopathy, and hyperviscosity syndromes occur at the same time. If CRVO occurs bilaterally, a careful clinical and complete examination should be done.
Other entities that should be ruled out are anterior ischemic neuropathy and ocular ischemia with venous stasis retinopathy caused by severe carotid artery obstructive disease. Most differential diagnosis difficulties are encountered with early, mild non-ischemic CRVO and late forms and complications that can mimic other conditions.
Treatment of CRVO is mainly focused on macular edema and also on neovascular glaucoma (NVG). NVG is a severe form of secondary glaucoma characterized by the proliferation of fibrovascular tissue in the anterior chamber. Many treatment options have been tried through the years, from systemic, local (ocular medication) to surgical ones.
Pan retinal photocoagulation (PRP), a laser treatment used to treat leaking blood vessels in the retina, can be performed in the case of neovascularization.
In the case of optic disc neovascularization or neovascularization elsewhere, PRP should also be performed to avoid anterior segment neovascularization and the consequent neovascular glaucoma.
In the case of optic disc neovascularization or neovascularization elsewhere, PRP can also be performed to avoid anterior segment neovascularization and NVG. It has been fully established in CVOS studies that preventive treatment does not stop iris and angle neovascularization.
Improvement of iris and anterior chamber angle neovascularization in response to PRP laser treatments is more likely to occur in eyes that have not been treated previously. The anterior chamber angle is a part of the eye located between the cornea and iris. Gonioscopy, the use of a special contact lens, is the standard procedure for examining the anterior chamber angle. It cannot be viewed in a routine slit-lamp examination because of the cornea’s optical properties.
The main treatments for macular edema and many retinal diseases are injections of a range of medications with a fine needle directly into the vitreous humor. Patients with Central Retinal Vein Occlusion should be seen monthly for 6 months to detect the onset of anterior segment neovascularization and establish prompt treatment.
If you are experiencing any vision loss or blurring in part or all of one eye suddenly or it becomes worse over several hours or days, make an appointment with your retinal specialist immediately. The vision loss or blurring is painless, so you may not think it is serious as it could be. Early treatment for CRVO is the best way to prevent a worsening condition and possibly blindness.