Constant Amplitude Electroretinography for the Determination of Retinal Sensitivity in Normal and Abnormal Subjects

Abstract

The goal of clinical electroretinography (ERG) should be to obtain rapidly a maxi­ mum amount of reliable information with minimal discomfort to the patient. Numer­ ous attempts have been made to accomplish this, but no one method has become generally accepted. Because at almost every clinic where electroretinography is used a proce­ dure has been devised that is specially modi­ fied for that clinic, and it is still virtually im­ possible to compare ERG data from different laboratories. Although it is easy to record the ERG, the origins of its components are still not fully understood. Using a contact lens electrode and capacitance coupled amplification, only two major electrical deflections constitute the ERG wave form as it is observed clinically. However, the criteria for classifying these responses as normal or abnormal vary widely. A useful diagnostic method depends upon developing such criteria quantitatively as well as qualitatively. The usefulness of a technique may be further extended by em­ ploying equipment and procedures that may be readily duplicated by other investigators. At low stimulus intensities the electroretinographic response is even simpler than it is at high intensities: the ERG consists only of a small corneal-positive deflection, the fawave; the corneal-negative a-wave does not appear until higher stimulus intensities are