Abstract
Purpose :
Imposing defocus on the retina triggers short-term changes in choroidal thickness that are assumed to predict future refractive changes, both in humans and animal models. Artificial visual stimuli, on the other hand, can uncouple choroidal thickness changes from changes in axial eye growth. It is therefore necessary to verify under which conditions thicker choroids can predict less myopia development.
Methods :
Seven day old chicks were kept in large plastic boxes (60x60x30 cm) with walls covered with 27” screens. Dynamic stimuli were presented on the screens and were also projected on the floor from above by two video projectors as described by Wang et al. (doi: 10.1167/iovs.18-26471). Checkerboard patterns with squares with repeated sawtooth-shaped temporal luminance profiles, either with a rapid ON or rapid OFF, were presented. Stimuli were applied at 3 different square sizes (68x39, 40x22, 28x16 squares/monitor) in combination with different cycle frequencies (0 Hz, 0.8 Hz, 1.2 Hz, 2 Hz, 3 Hz, 5 Hz, 8 Hz). SD-OCT (HRA+OCT Spectralis) was used to measure choroidal thickness in alert animals at baseline and 3 hours after treatment. A multi-factor ANOVA was used to determine the influence of size, frequency and character (ON/OFF) on choroidal thickness (ChT) changes.
Results :
The size of the stimuli had a significant main effect (delta ChT: smallest size: -26.4±1.6 µm, medium size: -6.9±2.14 µm, largest size: -15.1±2.3 µm). Changes in ChT were also significantly influenced by the stimulus frequency with the strongest effect at 3 Hz (-30.2±4.6 µm) and smallest at 2 Hz (-12.1±3.3 µm). The interaction between frequency and size was also significant. Comparing all treatment groups, only one of the stimuli (1.2 Hz ON, medium size) caused an increase in choroidal thickness (+4.75±6.5 µm) while OFF stimuli at this field size and frequency caused the thinnest choroids (-41.6±6.2 µm).
Conclusions :
Dynamic artificial stimuli of different frequency, size and ON/OFF characteristic influence choroidal thickness in a complex way. Except for one stimulus (1.2 Hz ON medium size), all others caused choroidal thinning which was partially explained by diurnal choroidal thickness changes during the examination period. Further experiments, using longer stimulation periods, are needed to fully describe the predictive power of choroidal thickness changes on axial eye growth.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.