EXPERIENCES WITH THE INTERNATIONAL STANDARD FOR CLINICAL ELECTRORETINOGRAPHY - NORMATIVE VALUES FOR CLINICAL-PRACTICE, INTERINDIVIDUAL AND INTRAINDIVIDUAL VARIATIONS AND POSSIBLE EXTENSIONS

The international Standard for Clinical Electroretinography requires a minimum of 5 standard response types. In a sample of 20 healthy subje cts, the normative values according to this standard were established. Since the distribution of amplitude and implicit time does not follow a Gaussian distribution, we have found the median value and the 1st t o 99th percentile or the 5th to 95th percentile useful for determinati on of abnormality, presented here separately for intraindividual and i nterindividual variation. To improve quality and reliability, we propo se that individual laboratories extend the minimum standard and record the standard responses as parts of a stimulus series of increasing in tensity. The normal value of the bia ratio can easily be established f rom the maximum response to the Standard for Clinical Electrophysiolog y standard flash, pointing to abnormalities especially in circulatory disturbances and in degenerative diseases of the retina. The bia ratio is between 1.5 and 1.7. If flicker responses are recorded at the 1st and 10th minutes after the onset of the rod saturating adaptation ligh t (25 cd/m(2)), an increase in amplitude can be observed, which in our sample has a relative value of 1.3. A reduced increase in cone respon se amplitudes during light adaptation might point to abnormality withi n the rod/cone interaction. Responses from the cone system can be furt her differentiated by the use of chromatic stimuli. With,appropriate f ilters, short-wavelength cone-sensitive and long-wavelength cone-sensi tive responses can be differentiated also in clinical daily practice, which might be helpful for further differentiation of cone disorders. Regular measurements of intraindividual variability can help to improv e the quality of electroretinogram recordings. Medians and ranges betw een the 1st and 99th and the 5th and the 95th percentiles were determi ned for all recordings for interindividual, as well as for intraindivi dual variations.