ABSTRACT
The electrophysiologic findings of ocular vascular disorders caused by vascular occlusion and neovascular proliferation are summarized in this chapter. The ERG is particularly useful in determining retinal damage from vascular occlusion when acute clinical signs are no longer present (Fig. 14.1). In addition, the ERG is helpful to assess the risk of neovascular development in central retinal vein occlusion. Retinal vasculitis disorders such as Behc¸et disease are discussed in Chapter 13. The outline of this chapter is as follows:
Vascular occlusions: Ophthalmic artery occlusion Central retinal artery occlusion Branch retinal artery occlusion Central retinal vein occlusion Branch retinal vein occlusion
Other proliferative neovascular disorders: Retinopathy of prematurity Diabetes retinopathy Sickle cell retinopathy
Other ocular vascular disorders: Hypertensive retinopathy Idiopathic polypoidal choroidal vasculopathy
VASCULAR OCCLUSIONS
The ophthalmic artery is a branch of the internal carotid artery and gives rise to the ciliary arteries and the central retinal artery. The ciliary arteries, in turn, give rise to the choroidal arteries and the choriocapillaris, a network of capillaries adjacent to the Bruch’s membrane and the retinal pigment epithelium. The choriocapillaris supplies the retinal pigment epithelium and the outer layers of the retina including the photoreceptor layer, outer plexiform layer, and the outer portion of the inner nuclear layer (see Chapter 1). The central retinal artery, which is visible at the optic nerve head, provides circulation to the inner layers of the retina including the nerve fiber layer, ganglion cell layer, inner plexiform layer, and the inner portion of the inner nuclear layer. The venous drainage from these inner retinal layers is provided by the central retinal vein. The ERG components such as the b-wave and oscillatory potentials have their origins in the inner retinal layers and are more likely to be selectively impaired when the retinal circulation provided by the central retinal artery and vein is disrupted. In contrast, the ERG a-wave, mostly a photoreceptor response, is impaired when
Figure 14.1 (Facing page) Fundus photograph, visual field and multifocal ERG of a 53-year-old woman who had complete amaurosis fugax of the right eye lasting 5min followed by almost complete recovery except for a persistent inferior area of blurred vision. Visual acuity was 20=20 in each eye and fundus appearance was normal. Visual field showed a consistent inferior defect. Multifocal ERG revealed impaired responses (circled) corresponding to the inferior visual field defect due to ischemic retinal damage. Further work-up with echocardiogram revealed patent foramen ovale and
choroidal circulation is compromised but is relatively spared if the retinal circulation is reduced.
