Focal electroretinograms and fundus appearance in nonexudative age-related macular degeneration. Quantitative relationship between retinal morphology and function

Background: The aim of this study was to evaluate the focal electroretinogram (FERG), an objective indicator of outer retinal function, in nonexudative age-related macular degeneration (NE-AMD), and to compare FERG results with morphological lesions assessed by stereoscopic fundus photographs and fluorescein angiograms. Methods: Twenty-five patients (25 eyes) with bilateral NE-AMD (visual acuity of the study eyes ≥ 0.4) as well as 10 age- and sex-matched control subjects (10 eyes) were evaluated. FERGs were recorded from the macular region (9°) in response to sinusoidal stimuli flickered at 32 Hz. Amplitude and phase angle of the Fourier-analyzed FERG fundamental component were measured. Fundus lesions were graded from color slides according to the Wisconsin age-related maculopathy grading system. Fluorescein angiograms were evaluated by an image analysis technique to compute the area with pathological hyperfluorescence (associated with drusen and/or retinal pigment epithelial atrophy) within the macular (approximately 9°x 9°) region. Results: Compared to control eyes, NE-AMD eyes had a reduction in the mean FERG amplitude (57% loss, P <0.001) with no phase changes. Amplitudes of individual affected eyes were negatively correlated with either the Wisconsin grading score (r = -0.63, P <0.001) or the percentage area of pathological hyperfluorescence (r = -0.70, P <0.01). Eyes with minimal NE-AMD lesions (Wisconsin score ≤ 6) and normal acuity had a lower mean amplitude (47% loss, P <0.05) than that of control eyes. Conclusions: The results indicate that, in NE-AMD, the FERG is altered in parallel with the extent and severity of fundus lesions. However, a functional impairment of outer macular layers, which is detected by FERG losses, could precede morphological changes typical of more advanced disease.