Although the bulk of blood flow into the eye goes to the choroid, perfusion abnormalities in the choroid are sometimes difficult to diagnose. Retinal vascular occlusion is readily visible by ophthalmoscopy and is straightforwardly confirmed by fluorescein angiography. Choroidal vascular occlusion, however, may produce changes that range from clinically evident to quite subtle. In addition, it is not uncommon for choroidal vascular abnormalities to be obscured by retinal vascular abnormalities such as cotton-wool spots and intraretinal hemorrhages. The entities that cause choroidal vascular abnormalities may affect the circulation from the ophthalmic artery to the choriocapillaris. Areas of ischemia and their watersheds tend to be vertically or horizontally hemispheric if they are caused by an intraorbital vascular occlusion. Intraocular vascular occlusions result in triangular areas of ischemia in the often oblique meridian of the occluded vessel. On rare occasions, choroidal blood flow abnormalities may be related to venous outflow problems. Diagnosis of choroidal blood flow abnormalities often requires angiography with both fluorescein and indocyanine green (Fig 6-2).
One of the most commonly seen groups of diseases that lead to choroidal vascular compromise are those that acutely cause severely elevated blood pressure, such as malignant hypertension or eclampsia. In addition to retinal abnormalities, patients with these diseases commonly develop serous detachment of the retina associated with areas of yellow placoid discoloration of the RPE (Fig 6-3). The perfusion abnormalities may range from focal infarction of the choriocapillaris to fibrinoid necrosis of larger arterioles. Although the choroid has a rich circulation, the blood flows in a functionally terminal fashion at the level of the choriocapillaris, so there is very little collateral flow after a focal occlusion. Resolution of smaller infarcts, which are tan in color initially, produces small patches of atrophy and pigmentary hyperplasia called Elschnig spots. Linear aggregations of these spots are called Siegrist streaks.
Inflammatory conditions, chiefly various types of arteritis, may affect the choroidal circulation as well. Giant cell arteritis may cause occlusion of one or more short posterior ciliary arteries, leading to broad triangular areas of choroidal nonperfusion in any meridian (Fig 6-4). Patients with this condition may have concurrent central retinal artery occlusion combined with nasal choroidal hypoperfusion, suggesting involvement of the first intraorbital segment of the ophthalmic artery. Wegener granulomatosis is a disorder characterized by necrotizing granulomatous lesions of the upper and lower respiratory tracts, glomerulonephritis, and generalized focal necrotizing vasculitis. Ocular manifestations occur in 30%–50% of patients and may include retinal vascular occlusion, choroidal vascular occlusion, or both (Fig 6-5).
Vaso-occlusion by microemboli may occur in a variety of diseases. In these entities, the choroidal circulation appears to be more affected than is the retinal circulation. Because of the rapid deceleration of the blood flow and the larger volumetric flow within the choroid, platelet emboli may be more likely to become lodged there. Thrombotic thrombocytopenic purpura causes a classic pentad of findings: microangiopathic hemolytic anemia, thrombocytopenia, fever, and neurologic and renal dysfunction. Patients with this condition may also have multifocal yellow placoid areas and associated serous detachment of the retina. A similar fundus picture may occur in patients with disseminated intravascular coagulation, where consumption of coagulation proteins, involvement of cellular elements, and release of fibrin degradation products lead to hemorrhage from multiple sites and ischemia from microthrombi.
On rare occasion, choroidal ischemia may result from iatrogenic causes. Thermal laser photocoagulation and, rarely, photodynamic therapy have also caused choroidal vascular occlusion with resultant segmental ischemia. Ocular compression related to cataract surgery has caused choroidal ischemia in some patients as well.
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