Chromatic pupillography in patients with Achromatopsia

Abstract

Purpose: The aim of the study was to characterize the function of rods, cones and intrinsic photosensitive retinal ganglion cells (ipRGCs) in patients with Achromatopsia by using a new, disease-specific protocol for chromatic pupillography.

Methods: 4 Patients with Achromatopsia were tested after 10 min light adaptation with stimulus duration of 4ms and 1s using short-wavelength (420nm; blue) and long-wavelength (605nm; red) with stimulus intensities of 0,01 lux corneal illumination. Higher illumination 28 lux was used for 1s short wavelength and long-wavelength stimulus. The same stimulus conditions were repeated after 20 min dark adaptation. For every stimulus the consensual pupil response was recorded by using Compact Integrated Pupillography (CIP by AMTech, Germany). Pupillary responses were compared with 4 age- matched controls. Relative amplitudes (percent of initial pupil diameter) of pupillary light reactions were evaluated as an average of four reliable pupil traces.

Results: After light adaptation, the stimulation with 4ms and 1s short-wavelength and long wavelength stimulus of 0,01 lux corneal intensity did not show any responses either in Achromatopsia patients or normal subjects. Compared to normal subjects, patients with Achromatopsia showed a reduction of the pupil response to 1s short-wavelength and long-wavelength bright stimulus (28 lux) in the light adapted state. In addition, after 1s short- wavelength light stimulus (28 lux) in dark adapted state Achromatopsia patients had smaller amplitudes compared to controls. Similar responses of patients with Achromatopsia and normal subjects were obtained after dark adaptation when using the long-wavelength stimuli of 28lux intensity. In contradiction, Achromatopsia patients showed higher amplitudes than normal controls to 4ms, 1s short-wavelength and long-wavelength light stimuli of 0,01 lux intensity in the dark adapted state.

Conclusions: Pupil responses to chromatic stimuli indicate a hypersensitivity of rod photoreceptors to low-intensity light stimuli after 20 minutes dark adaptation (Achromatopsia patients compared to controls). The presented stimulus protocol for chromatic pupillography seems an easy applicable, non-invasive tool for the diagnosis of Achromatopsia. As an objective and easy test method it may be useful for clinical trials with novel interventions in order to monitor treatment effects in Achromatopsia patients.