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Examination of the eye provides invaluable information for the diagnosis and monitoring of systemic disease. Nowhere else in the body can a microcirculatory system be directly visualized, investigated with such precision or neural tissue so easily examined, and nowhere else are the results of minute focal lesions so devastating. Many systemic diseases involve the eyes, and therapy demands some knowledge of the vascular, rheologic, and immunologic nature of these diseases.
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Normal Anatomy & Physiology
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The blood supply to the eye is from the ophthalmic artery, which is the first branch of the internal carotid artery (see Chapter 1). The first branches of the ophthalmic artery are the central retinal artery and the long posterior ciliary arteries. The retina is perfused by retinal and choroidal vessels that provide contrasting anatomic and physiologic circulations. The retinal arteries correspond to arterioles in the systemic circulation. They function as end arteries and feed a capillary bed consisting of small capillaries (7 μm) with tight endothelial junctions. Dependent on this anatomic arrangement is the maintenance of the blood-retina barrier, and this system is autoregulated, there being no autonomic nerve fibers. Most of the blood within the eye, however, is in the choroidal circulation, which is characterized by a high flow rate, autonomic regulation, and an anatomic arrangement with collateral branching and large capillaries (30 μm), all of which have fenestrations in juxtaposition to Bruch's membrane. Examination of the retinal vessels is facilitated by the use of red-free light and fluorescein angiography, whereas indocyanine green angiography gives further information about the choroidal vessels.
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Clinical Manifestations
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The sources of fundal hemorrhages may be arteries, capillaries, or veins, and their configurations depend on the site and severity of the disruption of vascular integrity (Figure 15–1). They usually indicate some abnormality of the retinal or choroidal vascular system but they may be caused by any condition that alters the efficacy of the endothelial barrier. The contribution of systemic factors should be considered in relation to (1) vessel wall disease (eg, hypertension, diabetes), (2) blood disorders (eg, thrombocytopenia, anemia, leukemia), and (3) reduced perfusion (eg, carotid artery–cavernous sinus fistula, acute blood loss).
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Preretinal Hemorrhages
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These result from damage to superficial disk or retinal vessels, which commonly are the consequence of retinal neovascularization, and are usually large with a crescentic shape, a gravity-dependent fluid level forming the superior border, and the extent of posterior vitreous ...