Statistical Analysis of ERG Amplitude and Waveform Abnormalities in Macular Degeneration

Abstract

Several previous studies have suggested that the dark adapted electroretino gram (ERG) may be abnormal in patients with macular degeneration (Krill, 1966; Merin & Auerbach, 1970; Orpin, Orpin & McCulloch, 1974; Ruedemann, 1966; Jacobson, Najae, Stephens, Kara & Gideon, 1960; Jayle, Boyer & Dubert, 1959; Niemeyer, 1969; Ruedemann & Noell, 1961; Henkes, 1956). Two types of abnormality have been reported: a reduction in the overall amplitude of all ERG components, and (Merin & Auerbach, 1970) a’ slowing’ of the a-wave. However, a critical examination of these reports raises some questions concerning the validity and interpretation of the findings. First, many of the reports are based on a more or less casual or ‘by eye’ comparison between relatively small numbers of ERG records from patients with macular degeneration and normals and lack adequate statistical tests. Second, the effect of age on the ERG has often been ignored in making comparisons. Third, the extent of the lesion observed ophthal-moscopically has not been carefully correlated to ERG findings. Since, it appears that ophthalmoloscopically visible abnormalities less than 3 disc diameters in extent usually do not produce ERG abnormalities (Jacobson, Najae, Stephens, Kara & Gideon, 1960; Francois & DeRouck, 1966; Ponte, 1961) this correlation is important. Finally, the considerable variability in ERG waveform from patient to patient has not received adequate attention.