Retinal vein occlusion

Retinal vein occlusion

Mary Kellogg Robinson

Retinal vein occlusion is second only to diabetic retinopathy as the most common form of retinal vascular disease in the United States.[1] Under the broad heading of retinal vein occlusion are several entities that can be distinguished by their anatomic and pathophysiologic features. It is important for the family physician to recognize and understand these entities, because they carry different prognoses.

Anatomy and Pathophysiology

Retinal vein occlusion may involve the central retinal vein, a branch retinal vein or a hemicentral vein. Hemicentral retinal vein occlusion occurs when one-half of a two-trunked central retinal vein becomes occluded in the anterior part of the optic nerve. Hemicentral occlusion is pathophysiologically similar to central retinal vein occlusion.[2]

Obstruction of venous flow most often occurs at or just behind the level of the lamina cribrosa. The central retinal vein is probably predisposed to occlusion at this point because the lumina of the central retinal artery and vein are in close proximity and are bound by a common adventitial sheath[3] (Figure 1). In addition, the lamina cribrosa, a sieve-like structure of connective tissue, provides support to the optic nerve, but also limits expansion and displacement of the nerve fibers and vessels that traverse its substance. Therefore, atherosclerosis of an adjacent central retinal artery in this area may cause impingement on the retinal vein. It is postulated that blood flow becomes more turbulent as the vein narrows, causing endothelial damage to the vein, exposing collagen, and initiating platelet aggregation and thrombosis.

In the retina, the branch retinal arteries and veins share a common adventitial coat. Atherosclerosis of the adjacent arteries may lead to venous endothelial damage, stasis and clot formation at arteriovenous crossings, the most common sites of branch retinal vein occlusion. Conditions that alter the viscosity of blood or result in abnormalities of clotting factors may also contribute to retinal vein occlusion.

Risk Factors

The major risk factors for retinal vein occlusion are age, hypertension, atherosclerotic vascular disease and diabetes mellitus.[4-7] Certain risk factors associated with atherosclerotic disease, such as cigarette smoking and hyperlipidemia, are also thought to increase the risk of retinal vein occlusion. Other conditions that predispose patients to retinal vein thrombosis include vasculitis, hyperviscosity syndromes and chronic glaucoma.

Less common factors that may influence thrombus formation, such as the use of oral contraceptives or the hemoconcentrating effects of diuretics, have also been linked to retinal vein occlusion. Antiphospholipid antibodies, lupus anticoagulant and anticardiolipin antibodies have been related to central retinal artery or vein occlusion and have been shown to be present in young patients (21 to 33 years of age) with amaurosis fugax.[8]

Central retinal vein occlusion may be unilateral or bilateral. In one study of 160 patients,[9] the incidence of bilateral retinal vein occlusion was found to be 10 percent. The risk factors associated with bilateral occlusion were the same as those for unilateral occlusion.

In one study,[10] hypertension was found to be associated with retinal vein thrombosis in patients younger than 40 years of age. However, the percentage of patients with no associated systemic disease was much higher in those under age 40 than in those over age 40 (Table 1).[9,11][TABULAR DATA OMITTED]

In a series of 17 patients under age 40,[11] patients with central retinal vein occlusion had a low incidence of underlying vascular or atherogenic disease. The investigators hypothesized that a congenital anomaly in the central retinal vein at the lamina cribrosa may underlie retinal vein occlusion in young patients; such an anomaly would cause turbulent blood flow and lead to thrombus formation.

Clinical Presentation

SYMPTOMS

Retinal vein occlusion can range from a subclinical condition to one with a marked reduction in central acuity. The visual loss is usually due to macular hemorrhages, edema or exudate. In most cases, peripheral vision remains intact.

PHYSICAL FINDINGS

The diagnosis of retinal vein occlusion is based on the presence of retinal hemorrhages and cotton-wool spots along the course of a dilated retinal vein. The process may involve only a small venous segment or a branch of the central retinal vein (Figure 2), several branches of the central retinal vein (Figure 3) or the entire central retinal vein (Figure 4). When the entire central retinal vein is involved, disk edema may be apparent. In the later stages of a retinal vein occlusion, arteriolar narrowing may also be noted.

Extensive hemorrhages and prominent cotton-wool spots are indicative of the ischemic form of retinal vein occlusion (Figure 5). In such cases, some degree of arteriolar insufficiency is thought to contribute to the clinical picture. The ischemic form tends to be associated with a more profound loss of acuity and field of vision. Unfortunately, in a number of cases, nonischemic retinal vein occlusion progresses to the ischemic form.[12]

In contrast to central retinal artery occlusion, in which visual loss is profound and retinal findings are relatively subtle, the findings in retinal vein occlusion are often striking and the visual dysfunction is mild.

COMPLICATIONS

While the initial clinical problems caused by retinal vein occlusion are related to macular changes, other problems may develop. Branch retinal vein occlusion can result in the proliferation of new vessels on the surface of the retina and the optic disk, which can lead to vitreous hemorrhage and retinal detachment. Central retinal vein occlusion can be associated with the proliferation of new vessels on the surface of the iris, which can lead to a form of recalcitrant, blinding glaucoma. In both circumstances, the release of vasoproliferative factors by an ischemic retina is thought to be responsible for new vessel formation.

Differential Diagnosis

Patients who present with signs and symptoms of retinal vein occlusion should be referred to an ophthalmologist. Referal is desirable to confirm the diagnosis and to assess the need for treatment.

The diagnosis of retinal vein occlusion must be considered when retinal hemorrhages, cotton-wool spots and venous dilatation along a branch or along the entire venous system are observed. Symptoms are usually limited to loss of central acuity. Other symptoms, such as tearing and eye pain, are unusual and suggest a different diagnosis.

In diabetic retinopathy, the pathology is usually concentrated about the posterior pole of the eye. The hemorrhages and cotton-wool spots do not follow a venous distribution, and venous dilatation usually is not prominent. In addition, characteristic sharply defined yellow exudates are often present.

One form of retinopathy associated with severe carotid insufficiency strongly resembles retinal vein occlusion. Some investigators have suggested that the only difference between the two conditions may be the marked drop in central retinal artery pressure (as determined by ophthalmodynamometry) that occurs in retinopathy of carotid occlusive disease. Characteristic symptoms of this condition include blurring of vision and other visual disturbances when the patient goes from a well-lighted room to a dimly lit room or from a dimly lit room to a more brightly lit room. Activities such as standing, walking, straining or looking upward also may provoke an episode of transient visual loss in patients with this condition.[13,14] It has been suggested that a slowing of retinal adaptation caused by retinal ischemia produces this light-induced visual loss. The patient may not volunteer this symptom unless a careful visual history is obtained.

Ancillary Examination Procedures

FLUORESCEIN ANGIOGRAPHY

Since the diagnosis of retinal vein occlusion is primarily a clinical one, the most important use of fluorescein angiography is in planning treatment. Neovascular complications in the retina and the iris are directly related to the amount of capillary nonfilling that can be found on fluorescein angiography (Figure 6 and 7). Photocoagulation therapy is sometimes used when a significant degree of capillary nonfilling is present.

OPHTHALMODYNAMOMETRY

Measurement of central retinal venous pressure provides an indirect assessment of the severity of obstruction. The absence of spontaneous venous pulsations, coupled with difficulty in compressing the central retinal vein following digital pressure on the globe, suggests the presence of elevated central retinal venous pressure. An ophthalmodynamometer can be used to obtain a quantitative measurement. Pressure will be increased with central retinal vein occlusion.

Ophthalmodynamometry can be used to assess central retinal arterial pressure. A characteristic feature of the ischemia of severe carotid artery disease is that central retinal arterial pressure will be low or not measurable. This can be seen on funduscopic examination when a gentle touch of the globe causes the artery to collapse.

APPLANATION TONOMETRY

Measurement of the intraocular pressure by applanation tonometry is important in the evaluation of a patient with retinal vein occlusion. The incidence of primary open-angle glaucoma is increased in patients with retinal vein occlusion. The increased intraocular pressure is thought to compromise venous flow and is a predisposing factor for thrombosis and increased intraocular pressure.

New vessel formation on the iris as a result of central retinal vein occlusion can lead to synechiae formation and secondary glaucoma. Neovascularization of the angle of the anterior chamber occurs frequently in patients with the ischemic form of central retinal vein occlusion. One detailed prospective study[15] found that approximately 40 percent of patients developed neovascular glaucoma by about one year after the onset of hemorrhagic retinopathy. The glaucoma that develops secondary to retinal vein obstruction is potentially preventable.

Management

Treatment for the acute phase of retinal vein thrombosis has included steroids, anticoagulants, streptokinase (Kabikinase), aspirin and plasma expanders. All of these approaches have generally been disappointing. Currently, the usefulness of tissue plasminogen activators in the treatment of retinal vein thrombosis is being evaluated in a multicenter trial.[9]

To prevent neovascularization, retinal photocoagulation is sometimes performed in patients with central retinal vein occlusion and extensive areas of capillary non-perfusion on fluorescein angiography. Established neovascularization of the retina and/or iris can be made to regress with panretinal photocoagulation.

Visual acuity can be stabilized, and at times even improved, by retinal photocoagulation in patients with persistent macular edema.

The small number of patients reported to have had bilateral occlusion hinders attempts to distinguish these patients from those with unilateral occlusion. However, some pertinent studies have shown a higher incidence of diabetes mellitus and uncontrolled hypertension in patients with bilateral retinal vein occlusion, compared with the incidence in patients with unilateral occlusion.[16,18] Therefore, the occurrence of unilateral occlusion mandates vigorous and aggressive steps to modify specific risk factors. Strategies include smoking cessation, lowering of serum lipid levels in patients with hyperlipidemia, alcohol restriction, and control of hypertension and diabetes mellitus.

REFERENCES

[1.] Schimeca GH, Magargal LE, Jaeger EA, Robb-Doyle E. An eye disorder caused by chronic cardiovascular disease. Geriatrics 1989; 44: 98-102. [2.] Hayreh SS, Hayreh SM. Hemicentral retinal vein occlusion. Arch Ophthalmol 1980;98: 1600-9. [3.] Sanborn GE, Magargal LE, Jaeger EA. Venous obstructive disease of the retina. In: Tasman W, ed. Duane’s Clinical ophthalmology. Philadelphia: Lippincott, 1990:1-24. [4.] Elman, MJ, Bhatt AK, Quinlam PM, Enger C. The risk for systemic vascular diseases and mortality in patients with central retinal vein occlusion. Ophthalmology 1990;97:1543-8. [5.] Cole MD, Dodson PM, Hendeles S. Medical conditions underlying retinal vein occlusion in patients with glaucoma or ocular hypertension. Br J Ophthalmol 1989;73:693-8. [6.] Gutman FA. Evaluation of a patient with central retinal vein occlusion. Ophthalmology 1983;90:481-3. [7.] Kohner EM, Cappin JM. Do medical conditions have an influence on central retinal vein occlusions? Proc R Soc Med 1974;67:1052-4. [8.] Digre KB, Durcan FJ, Branch DW, Jacobson DM, Varner MW, Baringer JR. Amaurosis fugax associated with antiphospholipid antibodies. Ann Neurol 1989;25:228-32. [9.] Quinlan PM, Elman MJ, Bhatt AK, Mardesich P, Enger C. The natural course of central retinal vein occlusion. Am J Ophthalmol 1990;110:118-23. [10.] Priluck IA, Robertson DM, Hollenhorst RW. Long-term follow-up of occlusion of the central retinal vein in young adults. Am J Ophthalmol 1980;90;190-202. [11.] Walters RF, Spalton DJ. Central retinal vein occlusion in people aged 40 years or less: a review of 17 patients. Br J Ophthalmol 1990; 74:30-5. [12.] Minturn J, Brown GC. Progression of nonischemic central retinal vein obstruction to the ischemic variant. Ophthalmology 1986; 93:1158-62. [13.] Kearns TP. Differential diagnosis of central retinal vein obstruction. Ophthalmology 1983; 90:475-80. [14.] Furlan AJ, Whisnant PJ, Kearns TP. Unilateral visual loss in bright light. An unusual symptom of carotid artery occlusive disease. Arch Neurol 1979;36:675-6. [15.] Hayreh SS, Rojas P, Podhajsky P, Montague P, Woolson RF. Ocular neovascularization with retinal vascular occlusion-III. Incidence of ocular neovascularization with retinal vein occlusion. Ophthalmology 1983;90:488-506. [16.] Pollack A, Dottan S, Oliver M. The fellow eye in retinal vein occlusive disease. Ophthalmology 1989;96:842-5. [17.] Kohner EM, Laatikainen L, Oughton J. The management of central retinal vein occlusion. Ophthalmology 1983;90:484-7. [18.] Dodson PM, Kubicki AJ, Taylor KG, Kritzinger EE. Medical conditions underlying recurrence of retinal vein occlusion. Br J Ophthalmol 1985;69:493-6.

The Authors

MARY KELLOGG ROBINSON, M.D. is an assistant professor of family medicine at the University of Florida Health Science Center, Jacksonville. A graduate of the University of South Florida College of Medicine, Tampa, Dr. Robinson completed a residency in family practice at St. Vincent’s Medical Center in Jacksonville.

JESSE I. HALPERN, M.D. is an associate professor in the Department of Ophthalmology at the University of Florida Health Science Center, Jacksonville. After graduating from the State University of New York College of Medicine in Brooklyn, Dr. Halpern completed a residency in ophthalmology at Montefiore Medical Center, New York City, and a fellowship in neuro-ophthalmology at Columbia-Presbyterian Medical Center, also in New York City.

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