Macular electroretinograms: their accuracy, specificity and implementation for clinical use

The pattern and the focal electroretinogram (ERG) are both non-invasive, electrophysiological responses recorded from circumscribed retinal areas and are most easily recorded from the macula. This paper describes how our department has incorporated these tests into our clinical protocol, shows how the recording technique and the method of electrode construction may be improved, and describes the normal limits of the macular responses we obtain. The ERG signal-noise ratio we obtained was better than that of the binocular visual evoked potentials (VEPs) recorded simultaneously. Pattern and focal ERGs, using improved methods of recording, show promise of being a valuable addition to the clinical investigation of subtle maculopathies and some forms of optic nerve dysfunction. Three illustrative cases are described. The first demonstrates normal macular ERG responses with abnormal Ganzfeld ERGs due to peripheral retinal damage. The second reveals differential pattern ERG reduction with normal focal ERG in recent optic neuritis. The third case demonstrates reversible simultaneous loss of Ganzfeld ERGs and macular ERGs in vitamin A deficiency.

Temporal acuity in normal and hearing-impaired listeners

Temporal acuity, defined as the minimum detectable gap in an otherwise continuous noise, was measured with an adaptive version of the two-alternative forced-choice task. For 6 normal listeners, the minimum duration detectable decreased from an average of 20.3 ms at a noise level of 30 dB SPL to 3.2 ms at 80 dB SPL. By comparison, the temporal acuity of 4 listeners with conductive hearing losses, 2 with otosclerosis, and 7 with sensorineural hearing losses, was poorer than that for normal listeners at equal sound pressure levels. At higher sound pressure levels, the acuity of those with conductive hearing losses or otosclerosis approached normal values, but the acuity for listeners with sensorineural hearing losses did not.