Abstract
Purpose :
A recent study in young human subjects (Swiatczak and Schaeffel, 2022) found that longitudinal chromatic aberration (LCA) is used by the emmetropic retina for the detection of the sign of defocus during emmetropization. We tested whether a similar stimulation paradigm would also be effective in freely ranging chickens.
Methods :
Seven chicks were kept in 27”x27” squared arena with each of its walls covered with a 27” screen. At the same time, a group of another seven chickens was filmed by a RGB camera (Logitec HD1060) and the camera output spatially filtered in real-time to simulate real and inverted longitudinal chromatic aberration (LCA). Spatial filtering included that either the red plane of the RGB signal was low pass filtered or the blue. As a control, the unfiltered output of the camera was used. Movies were displayed on the four screens of the arena but also projected on the floor from above by a video projector (Wang et al., 2019). Chicks were exposed to each of the 3 stimuli for 30 min on 3 consecutive days at age 14-16. SD-OCT (HRA+OCT Spectralis) was used to measure choroidal thickness (ChT) in alert animals at baseline (1.30 p.m.) and after treatment (2 p.m.). A one-way ANOVA was used to analyse treatment effects.
Results :
Baseline choroidal thickness of right and left eyes was significantly correlated at days 14-16. All treatments produced only small changes in choroidal thickness. After 30 minutes of exposure to unfiltered movies, choroidal thickness increased by +5.42 ± 3.77 µm (mean ± SEM). However, neither blue low pass filtered nor red low pass filtered movies induced significant changes compared to the control condition, or compared to each other (red low pass filtered: +3.42 ± 3.24 µm; blue low pass filtered: +7.33 ± 2.70 µm, One-way ANOVA: p = 0.51).
Conclusions :
Different from recent studies in humans, the choroids in chicken eyes did not respond to simulated LCA in a similar experimental paradigm. However, there are a number of possible reasons that need to be considered out before we can conclude that the chicken retina does NOT use LCA for emmetropization: (1) comparison of focus in blue and red may involve the UV-cones and they were not stimulated in our setup, (2) the LCA function used was based on human, not chick data, (3) we did not establish a baseline choroidal thickness before the treatments with a normalized input, and (4) exposure times may have been too short.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.