Chromatic pupillometry as highly sensitive testing method of photoreceptor function in retinal dystrophies

Abstract

AbstractPurpose Objective methods for the characterization of photosensitive cells are highly needed in patients with retinal dystrophies. The pupil light reflex is driven by rod, cone, and intrinsic photosensitive retinal ganglion cell (ipRGC) input. The aim of this study is to analyze two protocols of chromatic pupillometry with differing stimulus paradigms to gather isolated functional information of the three cell populations in patients with different forms of retinal dystrophies.Methods The study group comprised 60 patients with different forms of retinal dystrophies, and 32 healthy probands. Patients were grouped according to their electroretinography (ERG) data. A custom made binocular chromatic pupillometer (Bino I, AMTech) connected to the Colordome Ganzfeld stimulator (Diagnosys LLC) was used to assess changes in pupil diameter in response to red (640nm) and blue (462nm) light stimuli.Results Patients who had no measurable scotopic ERG also had the most reduced yet often still measurable rod‐weighted pupil responses (PR), while patients with abnormal or normal scotopic ERG had reduced or normal rod‐weighted PR. Similarly, patients with no measurable photopic ERG had reduced but still measurable cone‐weighted PR, while patients with abnormal of normal photopic ERG had mostly normal cone‐weighted PR. Reduced ipRGC‐weighted PR could not be correlated with the ERG classification.Conclusion In the absence of a measurable ERG, chromatic pupillometry generates important functional and quantifiable data on residual rod and cone activity. These data show that this technique should be added to the panel of examination tools for the characterisation of retinal dystrophies and for quantifying the clinical benefit of experimental treatment protocols.