I. Impaired dark adaptation in symptomatic carotid artery disease

It has been known for more than a century that even slight hypoxemia reduces dark adaptation. We studied dark adaptation in symptomatic carotid artery disease. Twenty-one consecutive patients scheduled for first-time carotid endarterectomy and 31 age-matched control subjects with normal carotid arteries were examined by dark adaptometry monocularly and were tested repeatedly on consecutive days. The average degree of internal carotid stenosis on the symptomatic side was much greater than that on the contralateral side. Dark adaptation was markedly impaired in the patients as compared with the control subjects. In the patients there was no difference in dark adaptation between the symptomatic and nonsymptomatic sides. The existence of carotid stenosis correlated to the level of dark adaptation. Pupillary size and age correlated to the dark adaptational level but did not affect the effect of carotid stenosis on dark adaptation. The decreased dark adaptation may be due to insufficient blood supply or repeated subclinical microembolization to the retinae, the brain, or both.