Correlation of infrared pupillometers and CCD camera imaging from aberrometry and videokeratography for determining scotopic pupil size

Abstract

We read with interest the article by Kohnen et al.1 on the assessment of the correlation of infrared pupillometers and CCD-camera imaging from aberrometry for determining scotopic pupil size. In the study, the authors used a Zywave aberrometer, which takes 3 consecutive measurements and calculates the mean. Being an investigational unit, this version of Zywave can electively turn off the illumination fixating target. It was concluded from the study that Zywave with the fixating target turned off gives the pupil diameter closest to the Procyon, although smaller in size. With the fixating target turned on, Zywave underestimates the pupil size significantly more. In our commercial version of Zywave software, version Zywave V5.09, there is a dynamic pupillometer that tracks the pupil size in real-time and records the largest pupil size during the tracking period. In our study of 19 eyes, the mean pupil size was 6.06 mm ± 0.78 SD using the Zywave and 5.70 ± 0.71 mm using Procyon. Using a pared sample t test, the difference was 0.36 ± 0.28 mm (P<.001). This shows a pupil size measurement with Zywave significantly larger than that with Procyon. We feel that using the largest recorded pupil size rather than the mean of the 3 may give a better representation for the scotopic pupil. After all, it is the largest natural pupil size we are interested in and it is this pupil size that one should cover in planning for refractive surgery to avoid side effects like glare.