[Quantitative assessment of the clinical electroretinogram]

The clinical application of electroretinography has been limited until now by the lack of standardisation, especially of stimulus conditions. Normal values for the electroretinographic response parameters can only be used if patients are examined under the conditions which were given for the examination of healthy subjects. It is shown in this paper that the inexpensive apparatus designed by Kooijman and Damhof (1981) can be calibrated by any user simply and at justifiable expense. Normal values for the amplitudes and peak times for the a- and b-wave are presented. The normal range of the values has been defined with regard to the frequency distribution. According to the authors' results, methods of descriptive statistics in skewed distributions are mainly necessary at low stimulus intensities. The descriptive methods for normal distributions were regularly applied at higher stimulus intensities. In general, however, ERG parameters are normally distributed as shown by the distribution of the residuals between the linear regression of the parameter to the logarithm of the corneal illuminance and the measured values. The influence of age on the amplitude was calculated according to the results of Lehnert and Wünsche (1966) and the lower limits of the normal range are given for four age groups. The data presented here may be used as normal values provided that the simple calibration methods are applied. Thus electroretinography is no longer a method merely for the laboratory, but can be used in clinics and offices as well. However, a prerequisite is that the physician has sufficient experience in ophthalmological electrophysiology.