Variations in calibration for computerized electronystagmography

The accuracy of the analyses of vestibular test results obtained from a com puterized electronystagmography (ENG) system depends on the accuracy with w hich the system has been calibrated to record the patient's eye movements. The variability of the calibration sensitivity was investigated by analysin g the records of 50 consecutive patients who attended for vestibular testin g and a study was carried out using 16 volunteer subjects to examine the co ntributions that time, changes in lighting and subject movement made to thi s variability. The effect of calibration frequency on the results obtained from caloric testing was also examined by analysing 16 patient records. The mean percentage change in sensitivity between the first two calibration s carried out on patients was found to be -17%, with a standard deviation o f 18%. However, there seems to be little baseline drift over time under con stant lighting conditions. Changes in lighting have a marked effect, and th e adjustment to lighting changes is slow. Gentle movement has little effect . Repeated calibration does not seem to be an effective method to control t he calibration-related errors in caloric test results. Careful control of room illumination and the use of adequate adaptation per iods to allow patients to adjust to the lighting should help to improve acc uracy but, even in the absence of satisfactory calibration, the use of a co mputerized ENG system can provide valuable diagnostic information.