Electroretinography, retinal ischaemia and carotid artery disease.
Reduction in the amplitude of oscillatory potential (OP) on the B wave of an electroretinogram (ERG) is a sensitive index of experimental retinal ischaemia and is being used clinically to evaluate the progression of diabetic retinopathy. This study assessed whether electroretinography could detect retinal ischaemia in a group of patients with normal fluorescein angiograms and carotid atherosclerosis. Two groups of patients were studied. Group A (n = 15) had carotid atherosclerosis on duplex ultrasonography while a matched control group B (n = 15) had normal vessels. All patients in Group A had flurorescein angiograms. ERGs were recorded bilaterally using a Ganzfeld stimulator and Medelec oscilloscope. The OP amplitudes were determined using the peak-nadir method. Of the 60 eyes examined, 18 had abnormal OPs and all of these occurred in Group A; ten associated with ipsilateral non-stenosing carotid lesions and eight with critical stenoses. Twelve had normal OPs in Group A, only one of which was associated with severe disease. The mean OP amplitudes were 292 mu and 198 mu in Group A and 172.89 mu and 115.6 mu in Group B (P less than 0.005 Wilcoxon Rank Sum Test). (Two readings reflect Medelec readings before and after computer adjustments.) This study demonstrates by electroretinography significant retinal ischaemia in the presence of normal fluorescein angiography in patients with proven carotid artery disease. Further evaluation is required to determine the relative importance of flow reduction and silent micro-embolisation in the genesis of this ischaemia particularly in relation to pre- and postoperative evaluation.