Purpose: To establish a feasible and sensitive pupillographic protocol to assess outer and inner retinal function for the first gene therapy trial in achromatopsia patients (ACHM) with mutations in CNGA3.
Methods: Twenty-seven CNGA3-ACHM patients and 22 age-matched control subjects were tested using chromatic pupillography. Three different protocols were established to assess the pupillary light reflex parameters and to create the final protocol. In the individual protocols, various stimulus parameters (i.e., intensity, duration, wavelength, adaptation states) were applied to evaluate the impact of these stimuli on the pupillary response in untreated ACHM patients.
Results: In the light-adapted conditions, CNGA3-ACHM patients showed significantly reduced maximal amplitudes compared with the control group when using a 1-second high intensity (28-lux corneal illumination) blue or red stimulus (P < 0.005). In the dark-adapted conditions, CNGA3-ACHM patients unexpectedly revealed significantly increased maximal amplitudes when stimulating with red (1 second) or blue (4 ms and 1 second) stimuli of low intensity (0.01-lux corneal illumination; P < 0.05). Pupil responses of CNGA3-ACHM patients after high intensity (28 lux) red and blue 1-second stimuli were within the normal range.
Conclusions: Chromatic pupillography demonstrated significant reduced pupil responses to stimuli addressing primarily cone function, an increased sensitivity to rod-favoring stimuli and evidence for disinhibition of intrinsically photosensitive retinal ganglion cells in CNGA3-ACHM patients. A final protocol was established based on these findings. These conclusions may be useful for the objective assessment of efficacy gained by gene therapy or other innovative interventions in this hereditary retinal disorder.