The fine structure of multifocal ERG topographies.

The multifocal electroretinogram (mfERG) allows for functional field mapping by concurrently deriving responses from a large number of retinal locations. The stimulus resolution most commonly used consists of 103 hexagonal elements. Here, we stimulated with an array of 509 elements. To determine the extent to which the multifocal ERG shows anatomical and physiological details, such as shadows cast by the retinal vasculature, we obtained mfERGs from two subjects using two different stimulus luminance levels and three light spectra. Good correspondence of some depressions with major blood vessels suggests relative angioscotomata. However, some reproducible local depressions cannot be attributed to blood vessel shadows cast on the retina, but more likely reflect local inhomogeneities in the physiological response characteristics.