Retinal Ischemia

Retinal ischemia

Introduction

Retinal ischemia is a condition where there is a reduced or lack of oxygen supplied to the retina. This can be caused by a variety of conditions including stroke, an accident, and diabetes. It is also commonly caused when the central retinal vein becomes detached from the eye, giving the blood that flows into the eye no where to go. When the retina loses its oxygen supply, the body tries to compensate by producing Vascular Endothelial Growth Factor. Unfortunately, this can lead to the growth of abnormal blood vessels on the surface of the retina, leading to blindness.

Who is at risk?

Retinal ischemia is a disease of the eye that typically strikes those who are middle aged or elderly. Also, systemic vascular disease is associated in 74% of patients with retinal ischemia greater than 50 years of age. Hypertension and hyperlipidemia are seen in 32-60% and diabetes in 15-34% of patients. In addition, migraine has been noted with increased prevalence in cases of CRVO, as have collagen vascular disorders and AIDS. Similarly, medications responsible include oral contraceptive pills, sympathomimetics and diuretics.

Causes of retinal ischemia

It can be caused by obstruction of the central retinal vein that leads to a backup of blood and fluid in the retina. For example, 23% of cases of retinal ischemia are found to be associated with ocular disease. These include primary open angle glaucoma in 25-66%, optic nerve disease, retinal artery occlusion, retinal vascular malformations which may lead to mural changes or cause a mass effect and uveitides including tuberculous, syphilitic and AMPPE. Trauma, either by sudden eyeball compression or change in intraocular pressure, may cause damage to the vessel wall by shearing or compressing the central retinal vein. Finally, retinal vasculitis may lead to vascular occlusion by a thrombotic or obliterative mechanism.

Symptoms of retinal ischemia

Typically, retinal ischemia begins suddenly without warning and is local to one eye but it often progresses to affect both eyes over time.

In most cases, a patient with retinal ischemia presents with a sudden, painless loss of visual acuity and visual field associated with optic disc swelling. The age range of patients with this condition is extensive, and depends in part on the cause of the ischemia. Some patients, however, simply experience sudden visual loss. The degree of visual loss may be severe or the patient may notice only a vague sensation of blurred vision, often described as a shade or veil over a portion of the visual field. Vision loss varies and may cause severe impairment in the visual field and visual acuity. Once occurred, the loss of vision is usually permanent although some recovery is possible in the early stages with appropriate treatment.


Treatment of retinal ischemia

Laser treatment: Traditionally, laser treatment is used as a treatment option. Often known as panretinal photocoagulation (PRP), this procedure may be used to prevent neovascular glaucoma, or secondary glaucoma, and to deter or reverse abnormal blood vessel growth in patients with CRVO. In PRP, a laser beam is used to ablate large sections of peripheral retina to, in effect, destroy that retina and thereby decrease VEGF production which will lead to resolution of abnormal blood vessels in CRVO that cause neovascular glaucoma and other problems.

Steroids: Steroids may be helpful in treating the underlying conditions of ischemic optic neuropathy, such as giant cell arteritis but this will do little to recover the loss of vision. A common steroid regimen consists of 40 to 60 milligrams per day (mg/d) of prednisone, depending on the patient. An initial dosage of 60 mg/d should be reduced by 10 mg every 2 weeks until it reaches 40 mg/d. This level should be maintained for two to four weeks and then reduced by an additional 5 mg/d every one to two weeks until it reaches 20 mg/d. From this point, reduce the daily dosage by 2.5 mg every one to two weeks until the dosage reaches 10 mg/d. The dosage of prednisone should then be tapered off by 1 mg per month until it is completely discontinued.

Surgery: If the cause of retinal ischemia is optic nerve neuropathy, the traditional surgical treatment has been fenestration (decompression) of the optic nerve although this treatment currently has few advocates. However, a biopsy of the temporal artery may be warranted to diagnose arteritis as the cause of the ischemic optic neuropathy.

Low Vision Rehabilitation: Because the ischemia generally can't be treated effectively, treatment for ischemic neuropathy involves rehabilitating decreased vision. There are four areas of rehabilitation: magnification, contrast, glare control and visual field loss. Special rehabilitators, including eyeglasses, magnifiers and sun filters may be recommended. Closed circuit television systems with magnifying effects may also be worn around the head to magnify objects.

Future therapies of retinal ischemia

While traditional therapies are frequently practiced in majority of the patients, newer modern therapies are also evolving with time. These include: Anti-VEGF drugs: Release of vascular endothelial growth factor (VEGF) contributes to increased vascular permeability in the eye and abnormal new vessel growth. Anti-VEGF treatment 2 helps decrease vascular permeability and edema and can prevent the abnormal growth of new blood vessels in the retina in patients with retinal ischemia. Clinical studies to test anti-VEGF therapy in retinal ischemia have been concluded successfully. There is one approved anti-inflammatory drug (Ozurdex) and one recently approved VEGF inhibitor (Lucentis, FDA approval in June 2010), for the treatment of retinal vein occlusion.

Chorioretinal Venous Anastomosis: Chorioretinal venous anastomosis, a procedure in which a bypass for the venous obstruction is created with the use of laser therapy, has been suggested for patients with perfused central retinalvein occlusion.

Prevention (What can be done to minimize the exposure)

While there are minimal treatments available, corrective measures may help improve vision, and new developments may help reduce the effects of retinal ischemia. It is essential to identify and treat any risk factors in order to minimize the risk to the other eye and prevent a further vein occlusion in the affected eye. Treatment of the above-mentioned risk factors (such as high blood pressure, increased blood cholesterol, smoking and high blood sugar) dramatically reduces the risk of a further vein occlusion in both eyes. Without treatment there is a high risk of recurrence causing further damage to the sight of the affected eye and also damaging the sight of the other eye. Furthermore, smoking may also help to cause blood pressure problems that lead to retinal ischemia.

Successful recovery rate

Studies and research show that approximately 40% of patients who experience retinal isechmia may have some improvement in vision in the weeks or months after the initial vision loss. However, approximately 20-25% of patients who are only affected in one eye will develop an ischemia in the other eye within three years.

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