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 visualized directly and investigated with such precision or neural tissue be examined so easily, 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.
NORMAL ANATOMY & PHYSIOLOGY
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 supplied by the retinal and choroidal circulations that have contrasting anatomic and physiologic characteristics. 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, which forms the blood-retina barrier, and they are autoregulated, there being no autonomic nerve fibers. However, most of the blood within the eye is in the choroidal circulation, which has a high flow rate, autonomic regulation, and an anatomic arrangement of 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 red-free light and fluorescein angiography, whereas indocyanine green angiography highlights the choroidal vessels.
The sources of fundal hemorrhages may be arteries, capillaries, or veins, and their appearance primarily depends on their location (Table 15–1 and Figure 15–1). They usually indicate 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 pressure (eg, carotid artery–cavernous sinus fistula, acute blood loss).
Preretinal hemorrhage due to ruptured retinal macroaneurysm. A: Large hemorrhage with fluid level lying between the retina and vitreous. B: Dispersion into vitreous after disruption of posterior vitreous with YAG laser.
Table 15–1.Types of Fundal Hemorrhage ||Download (.pdf) Table 15–1. Types of Fundal Hemorrhage
|Type ||Location ||Source ||Shape ||Color |
|Preretinal (subhyaloid) ||Between the retina and the vitreous ||Superficial disk or retinal vessels usually due to neovascularization ||Crescent with gravity-dependent upper border and round lower border determined by the extent of posterior vitreous detachment ||Light red to dark ...|