In cases of complete central retinal artery occlusion (CRAO), the ERG consists of a normal or supernormal a-wave and a markedly reduced b-wave . However, this is not the case in most patients . Platelet-fibrin and cholesterol are the major types of emboli, and both are soft and consequently quickly become fragmented and cast into the distal radicles of the retinal circulation. As a result, by the time the patient is examined fluorescein angiogra-phy often fails to detect complete obstruction of the central retinal artery.
The ERGs elicited by a single bright flash (mixed rod and cone ERG), the visual fields, and visual acuities of five patients with CRAO are shown in Fig. 3.14. Despite the extremely constricted visual fields and poor visual acuity, the ERGs in the affected eyes are well preserved. Although the b/a ratio in the affected eyes is lower than that of fellow eye, none of the ERGs from the affected eyes has a negative configuration. These results suggest that the function of the retinal layer related to the ERG can recover to some degree following recovery of the retinal
Fig. 3.14. Mixed rod-cone (bright flash) ERGs, visual fields, and visual acuity (right) obtained from the affected eye and normal fellow eye of five patients with central retinal artery occlusion (CRAO). Despite the severe decrease of the subjective visual functions, the ERGs are relatively well preserved
Fig. 3.14. Mixed rod-cone (bright flash) ERGs, visual fields, and visual acuity (right) obtained from the affected eye and normal fellow eye of five patients with central retinal artery occlusion (CRAO). Despite the severe decrease of the subjective visual functions, the ERGs are relatively well preserved circulation, as demonstrated by fluorescein angiography. However, because the ganglion cells are more vulnerable to ischemia, they suffer irreversible damage soon after the occlusion. Thus, the marked deterioration of the subjective visual function in patients with CRAO may result largely from the damage to ganglion cells.
The fundus appearance of ophthalmic arterial occlusion is similar to that of CRAO in the acute stage. However, when the ophthalmic artery is occluded, not only central retinal artery circulation but also choroidal circulation is disturbed, resulting in marked deterioration of the a-wave . This finding is important for differentiating CRAO from ophthalmic arterial occlusion.
Electrooculography (EOG) of CRAO shows a depressed light rise with a low base value. This finding indicates that the mid-retinal cells necessary for detecting the EOG light rise are compromised, producing an abnormal light peak/dark trough (L/D) ratio [3,4].
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