Purpose: The aim was to investigate the involvement of intrinsically photosensitive retinal ganglion cells (ipRGCs) in patients with manifest glaucoma and ocular hypertension (OH) using specific parameters of the pupil light reflex to chromatic stimuli.
Methods: Twenty-five patients with manifest glaucoma, 16 patients with OH and 16 healthy control subjects were stimulated with 28 lx red (605 nm) or blue (420 nm) light with a duration of either 1 s or 4 s. The consensual pupil light reaction was recorded by means of infrared pupillometry. The maximal relative amplitude (MRA), the post-illumination pupil response PIPRblue-red, and the slope of the response during exposure to the 4 s red stimulus (SORRS) were calculated and compared using ANOVA and Tukey-Kramer post-hoc tests. Correlations between pupil parameters and visual field defects were analyzed using Pearson correlation coefficient r.
Results: PIPRblue-red was reduced in glaucoma patients compared to normals (p < 0.001) and OH (p < 0.01). There was no significant difference between OH and normals. Glaucoma patients showed additionally reduced MRA for red and blue light (p < 0.05) and a pupillary escape during exposure to red light (increased SORRS, p < 0.0005). This pupillary escape could also be seen in single subjects with OH. Significant correlations between pupil parameters and visual field defects were detected.
Conclusions: The reduced PIPRblue-red indicates a characteristic impairment of the melanopsin-driven pathway of ipRGCs in glaucoma patients, whereas the reduced MRA and increased SORRS suggest a disturbed synaptic function and altered interaction between outer photoreceptors, RGCs, and ipRGCs.
Keywords: Colour pupillography; Glaucoma; Ocular hypertension; Pupil light reflex; ipRGC.