Factors affecting the post-illumination pupillary response: implications for glaucoma

The post illumination pupillary response (PIPR) is a sustained pupil constriction to short-wavelength blue light. This response has been reported to be mediated by a unique subset of atypical photoreceptor cells named intrinsically photosensitive retinal ganglion cells (ipRGCs). Although previous studies have shown that the PIPR is affected in people with glaucoma, many aspects of the PIPR are still unclear, including what factors affect this response. Therefore, it was the aim of this thesis to ascertain if PIPR is affected by other factors that affect glaucoma such as age, gender and iris colour. This thesis uses a novel, quick and non-invasive pupillometer that was developed to measure the PIPR in a normative population, people at risk of glaucoma and people diagnosed with glaucoma. The pupillometer comprised of a 5Mp InfraRed (IR) camera, two IR LEDs and four blue LEDs, controlled by a Raspberry Pi computer. Stimuli consisted of a 1.5s pulse of blue light. The right pupil of the participant was video recorded using the camera. Measurements were preceded by a period of 10 mins of dark adaptation (<5 lux). PIPR was quantified as the relative difference from baseline pupil size, with a decreased pupillary response yielding a higher numerical value. The PIPR was quantified using a range of metrics including maximum constriction, transient pupillary light reflex (PLR), PLR latency, peak constriction amplitude, recovery at 6s and area under the curve. Other novel metrics not yet reported in the literature were also investigated, such as recovery at 2s, 4s and 8s, maximum constriction and dilation velocities and immediate dilation velocity. The results suggest that gender significantly affects recovery of PIPR at 6s, whereas age and iris colour do not affect any of the investigated metrics. Glaucoma was shown to significantly decrease the transient PLR. These findings improve our understanding of the PIPR in normal, healthy people and this work increases our understanding of what risk factors for glaucoma influence PIPR.