Chapter 1: Ocular disease or neurologic disease? |
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Figure 1.16 Retinal changes associated with branch retinal artery occlusion. (A) There is a sharp demarcation between the area of acute retinal infarction, which appears white due to edema, and the normal adjacent retina. (B) Confluent cotton-wool spots represent focal infarcts of the nerve fiber layer.
occlusion, the entire posterior retina is thickened and white except for a central cherry-red spot which is due to preserved flow in the choroidal circulation that supplies this area. In the chronic phase, after retinal edema has resolved, differentiating between retinal and optic nerve ischemia may again be difficult. Because of retrograde axonal degeneration, in the wake of a retinovascular event the optic disc will appear pale, either focally or diffusely. In this stage, electrophysiologic testing, usually with the mfERG, can be helpful for making this distinction.
Diagnosis: Hyperacute central retinal artery occlusion
Tip: In a hyperacute retinal artery occlusion, the retina may have a normal appearance.
Hazy night vision
Case: Over a six-month period this 55-year-old postal worker noticed slowly progressive “haziness” of vision in both eyes, especially in dim illumination. This became so severe that he started using a nightlight and stopped driving after dark. He had no head or eye pain, focal neurologic deficits or systemic symptoms. His medical history
was positive for hypertension, hypercholesterolemia and previous morbid obesity for which he had undergone gastric bypass surgery 12 years earlier. Visual acuity was 20/25 OU with normal color vision and pupillary responses. Goldmann perimetry showed mild superior depression, and dilated fundus examination was normal (Figure 1.17). A fluorescein angiogram and ocular coherence tomography (OCT) were also unrevealing. Based on the negative ophthalmic work-up, a neurologic cause was suspected and the patient was referred for neurologic evaluation. An MRI showed a few white matter lesions consistent with small vessel disease but was otherwise normal.
What specific aspect of this patient’s history suggests the correct localization of his visual problem?
Difficulty seeing at night (nyctalopia) strongly suggests retinal disease, specifically a disorder of photoreceptors preferentially involving the rods. In this patient, a full-field electroretinogram (ERG) showed markedly reduced amplitudes on scotopic testing and mild reduction on photopic testing, confirming rod dysfunction (Figure 1.18A). A serum retinol
20 Chapter 1: Ocular disease or neurologic disease?
Figure 1.17 Goldmann perimetry in a 55-year-old postal worker with decreased night vision. There is mild superior depression affecting central and mid-peripheral isopters in both eyes.
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Figure 1.18 Full-field scotopic ERG in the left eye of the above patient. (A) At initial testing, the amplitude of the b-wave is decreased at 180 µV. (B) Following treatment with vitamin A the b-wave amplitude has increased to 380 µV.