Determining scotopic pupil size

Abstract

Reply: We thank Cheng and coauthors for their comments on our comparison of devices to determine scotopic pupil sizes. The Zywave unit used by them (commercial software 5.09) is different than the one used in our study (software 4.45SP2). Using the pupillometry function, software 5.09 has no fixation target light and the infrared laser runs continuously at 2 μw of power during the measurement. Software 4.45SP2 has no fixation target light, and the infrared laser runs at 2 μw continuously and then at 35 μw for 100 ms during each measurement. In our study, the measurement was the diameter of 3 averaged wavefront readings. However, even in the continuously running setup of the commercial system, there is variation in pupil size due to hippus that is on the order of the changes in pupil size one sees between the 3 measurements. Day-to-day variations may be larger than the differences Cheng and coauthors question in our measurements. It might be correct to use the largest recorded pupil size rather than an average for a better representation of the scotopic pupil size, but in the study by Cheng and coauthors, the mean Zywave measurement was compared to the scotopic Procyon measurement, which represents the mean and standard error of 10 images acquired in 2 seconds at an illuminace level of 0.04 to 0.07 lux.1 Thomas Kohnen MD Evdoxia Terzi MD Thomas Kasper MD Eva-Maria Kohnen MD Jens Bühren MD