Abstract
Purpose:
Pre-selected light stimuli were used to characterize the pupillary light reflex (PLR) and monitor its modification during retinal degeneration in the Rho-/- mouse model.
Methods:
Wild type SV129 (n=6 to 9) and Rho-/- mice (n= 4 to 9, age 1 month to 6 months) were all tested following overnight dark adaptation. An alternating, full-field red and blue light of short duration (500 milliseconds) and of increasing intensity over 4 log-units was used to stimulate one eye. The pupil response of the stimulated eye was recorded continuously using the A2000 Neuroptics system. The initial response during the first 2.5 seconds (s) following the stimulus onset was described from maximal contraction amplitude and the dynamics of immediate recovery from this maximal contraction.
Results:
Compared to wild type mice, one month-old Rho-/- mice showed decreased maximal contraction amplitude to all blue and red light stimuli except at the highest intensity blue stimulus (2 loglux). With increasing age and progressive photoreceptor degeneration, the amplitude of this maximal contraction and the dynamic of the initial response are differently affected depending on the intensity and wavelength of the stimuli. Following low and intermediate red stimuli, the maximal contraction was reduced drastically while contraction amplitude to high intensity red stimuli remained relatively prserved. Following low blue stimulation, the contraction amplitude is maintained despite the progression of the photoreceptor degeneration. However, the early dynamic of the initial response is modified with age with the loss of the characterized rapid partial recovery observed with the first 2.5 s revealing the loss of photoreceptor input to the initial response.
Conclusions:
The Rho-/- model to study PLR responses provides one model to study functional responses during the selective and sequential loss of rods and cones. With progressive rod and cone loss, the input of melanopsin photoreception to the pupil light reflex proportionately increases and may be the only remaining photosensitive cells at end-stage. The loss of photoreceptors during degeneration in the Rho-/- model affects the PLR response to blue light differently compared to red stimuli.