Purpose: To compare the limits of normality of the electroretinogram (ERG) amplitude and implicit time of two different laboratories. Methods: Normative ERG data from LKC Technologies, which uses UTAS software were compared to normative data from our laboratory using LKC equipment (EPIC 2000). The former included 110 normal subjects with ages ranging from 22 to 79 years and the latter included 42 normal subjects ranging from 6 to 72 years of age. Single flash ERG using ISCEV (International Society of Clinical Electrophysiology of Vision) recommended routine with ERG-jet contact lens electrodes were performed in both laboratories. Results: All ERG amplitude parameters, as well as all implicit times were significantly different (p< 0.0001) between both laboratories with the exception of the oscillatory potentials' amplitudes (p = 0.0779) and the b-wave implicit times of the maximal combined response (p = 0.7771). Conclusions: Each electrophysiology laboratory should have its own normal limit standardization, which can be determined either by the 95% confidence interval of its normal data sample, or the 2.5 and 97.5 percentiles. The former is narrower and therefore more sensitive, the latter has a much broader range and therefore is significantly less sensitive.
Electroretinography; Electrophysiology; Reference values; Confidence intervals; Comparative study
