First results of automated RAPD-SWIFT method in dynamic pupillometry

This paper presents preliminary observations on the use of a commercial pupillometric instrument (Albomed PupilX) for the detection and quantification of Relative Afferent Pupillary Defect (RAPD). In this pilot study, video-based pupillometry was used in conjunction with calibrated LED illumination to simulate the effects of the traditional swinging-flashlight test using neutral density filters.

The results presented in this study follow a method described by Wilhelm et al. (Tübingen SWIFT-test) in which the eyes are illuminated alternately and the response in pupil diameter measured by video pupillometry. Using the PupilX instrument, the LED intensity can be programmed in logarithmic steps starting from a maximum intensity of 1000 lux (lx), with each reduction of 50% in illumination intensity corresponding to a 0.3 log-units increase in filter density.

The eyes were stimulated unilaterally with illumination intensities corresponding to a neutral density range of 0.0 to 0.9 log-units. In all normal subjects a symmetrical pupil reaction was seen, independent of which eye was stimulated. In contrast, in a subject with known RAPD, a clear asymmetry in the reaction to stimulation of the left and the right eyes was seen.

These measurements were compared with typical results from the original Tübingen SWIFT study and good qualitative agreement was seen. Furthermore, the method can clearly differentiate between healthy subjects and those with a known RAPD, indicating that the PupilX, programmed with specific stimulus sequences and in conjunction with a suitable analysis software, has the potential for recognition and quantification of RAPD, and prompting the suggestion for further study involving a range of patients including both normal subjects and those with a known and quantified RAPD.