Purpose
The post-illumination pupil response (PIPR) is an index of melanopsin-driven intrinsically photosensitive retinal ganglion cell (ipRGC) activity. Hemifield analysis of PIPR may have important clinical implications. We developed a novel method to induce PIPR during hemifield stimulation and evaluated the test-retest reliability of current methods of measuring PIPR under hemifield, central-field and full-field stimulation.
Methods
Pupil response was recorded with an eye tracker in 10 visually normal subjects (6 females, mean age 30 years, range 19-56). Light stimuli were presented using a Ganzfeld screen with a custom built device to control the extent of retina being stimulated. Blue light stimulation at 400 cd/m2 intensity was presented for 400 ms to the lower and upper halves of the central 30° (hemifields), central 30° (central-field) and full-field to induce PIPR. Red full-field stimulations at the same intensity and duration were also presented as an internal control condition. Test-retest reliability of the PIPR measures were assessed by calculating the intra-class correlation coefficient (ICC) of 6 repetitions for lower and upper hemifield stimulation, and 3 repetitions for central-field and full-full stimulation.
Results
Hemifield, central-field and full-field blue light stimulation induced increasingly greater PIPR in ascending order , while full-field red light stimulation induced no PIPR. Mean lower and upper hemifield PIPR were highly symmetric (Figure 1). Mean ICC of blue light PIPR was 0.87 for lower/upper hemifield, 0.88 for central-field, and 0.94 for full-field stimulation.
Conclusions
We described a convenient yet reliable method to measure PIPR induced by hemifield, central-field and full-field light stimulation. Good PIPR measurement reliability was obtained under all viewing area conditions. This protocol will facilitate the clinical applications of PIPR testing.