Changes in choroidal thickness and blood flow in response to form deprivation‐induced myopia and repeated low‐level red‐light therapy in Guinea pigs

Abstract Purpose To evaluate ocular refractive development, choroidal thickness (ChT) and changes in choroidal blood flow in form‐deprived myopia (FDM) Guinea pigs treated with repeated low‐level red‐light (RLRL) therapy. Methods Twenty‐eight 3‐week‐old male tricolour Guinea pigs were randomised into three groups: normal controls (NC, n = 10), form‐deprived (FD, n = 10) and red light treated with form‐deprivation (RLFD, n = 8). Interocular refraction and axial length (AL) changes were monitored. Optical coherence tomography angiography (OCTA) measured choroidal thickness, vessel area density, vessel skeleton density and blood flow signal intensity (flux) in the choriocapillaris and medium–large vessel layers. The experimental intervention lasted 3 weeks. Results At week 3, the FD group had higher myopia and longer axial length than the NC group (all p < 0.001). The RLFD group had higher hyperopia and shorter axial length than the FD group (all p < 0.001). At week 1, the NC group had a thicker choroidal thickness than the FD group ( p < 0.05). At weeks 2 and 3, the RLFD group had a thicker choroidal thickness than the FD group ( p = 0.002, p < 0.001, respectively). Additionally, the NC group had higher vessel area density, vessel skeleton density and flux in the choriocapillaris layer than the FD group at the three follow‐up time points (all p < 0.05). At week 3, the vessel skeleton density and flux were higher in the RLFD group than in the FD group (all p < 0.05). Correlation analysis results showed that weekly changes in refraction and choroidal thickness were negatively correlated with changes in axial length (all p < 0.05). Choroidal thickness changes were positively correlated with alterations in the vessel area density, vessel skeleton density and flux in the choriocapillaris layer, as well as vessel skeleton density and flux changes in the medium–large vessel layers (all p < 0.05). Conclusions Repeated low‐level red‐light (RLRL) therapy retards FDM progression in Guinea pigs, potentially through increased choroidal blood flow in the choriocapillaris layer.