Assessment of multifocal electroretinogram abnormalities and their relation to morphologic characteristics in patients with large drusen

Objectives: To determine the extent of functional changes in the first-order kernel multifocal electroretinogram (mfERG) responses in patients with large drusen by means of a localized analysis and to determine correlations between mfERG responses and morphologic changes. Methods: Thirty-one eyes from 20 patients ages 58 to 84 years with large drusen (≥5 drusen ≥63 μm diameter) were studied. The mfERGs were recorded with a stimulus of 103 hexagons and a flash intensity of 2.67 candela (cd)·s^-1·m^-2. Each of the 103 single first-order kernel mfERG responses was analyzed and compared with those of age-matched healthy control subjects. Imaging studies, including color stereo fundus photography, red-free fundus photography, and fluorescein angiography, were performed in all patients, and morphologic changes (drusen in red-free fundus photography, staining or window defect in fluorescein angiography) were determined with a digital measurement tool. The mfERG responses were correlated to areas with and without morphologic changes. Results: Reduced responses were found in 10.0% (scalar products) and 4.0% (response densities) and delayed implicit times in 13.8% (N1), 18.9% (P1), and 23.8% (N2) of all mfERGs. Abnormal mfERG responses extended up to 25° in radius. Significant morphologic-functional relations were detected in only a few patients. Abnormal mfERG variables were present in areas without morphologic changes. Conclusions: Patients with large drusen exhibit functional changes in the cone-driven pathways evaluated by the mfERG, indexed particularly by implicit times. Morphologically visible changes do not predict retinal function. Large drusen are associated with a more general retinal dysfunction.