Optical Defocus Rapidly Changes Choroidal Thickness in Schoolchildren

Abstract

The current study aimed to examine the short-term choroidal response to optical defocus in schoolchildren. Myopic schoolchildren aged 8-16 were randomly allocated to control group (CG), myopic defocus group (MDG) and hyperopic defocus group (HDG) (n = 17 per group). Children in MDG and HDG received additional +3D and -3D lenses, respectively, to their full corrections on the right eyes. Full correction was given to their left eyes, and on both eyes in the CG. Axial length (AXL) and subfoveal choroidal thickness (SFChT) were then measured by spectral domain optical coherence tomography. Children wore their group-specific correction for 2 hours after which any existing optical defocus was removed, and subjects wore full corrections for another 2 hours. Both the AXL and SFChT were recorded hourly for 4 hours. The mean refraction of all subjects was -3.41 ± 0.37D (± SEM). SFChT thinned when exposed to hyperopic defocus for 2 hours but less thinning was observed in response to myopic defocus compared to the control group (p < 0.05, two-way ANOVA). Removal of optical defocus significantly decreased SFChT in the MDG and significantly increased SFChT in the HDG after 1 and 2 hours (mean percentage change at 2-hour; control vs. hyperopic defocus vs. myopic defocus; -0.33 ± 0.59% vs. 3.04 ± 0.60% vs. -1.34 ± 0.74%, p < 0.01). Our results showed short-term exposure to myopic defocus induced relative choroidal thickening while hyperopic defocus led to choroidal thinning in children. This rapid and reversible choroidal response may be an important clinical parameter in gauging retinal response to optical defocus in human myopia.

Fig 1. Study design.

Baseline measurements including refractive errors (Rx), axial length (AXL) and OCT images were taken after cycloplegia. Subjects were randomly assigned into control, myopic defocus or hyperopic defocus group and defocus lenses were worn for 2 hours using trial lenses. Defocus lenses were then removed after 2 hours of lens wear. AXL and OCT images were acquired every hour.

Fig 2. A representative OCT image showing choroid using enhanced depth imaging (EDI) mode.

Subfoveal choroidal thickness was determined manually by two independent experienced observers using built-in software.

Fig 3. Changes in subfoveal choroidal thickness (SFChT) and axial length (AXL) in response to optical defocus.

Percentage change vs. baseline in SFChT (A) and AXL (B) in control group (CG), myopic defocus group (MDG) and hyperopic defocus group (HDG) during the study. DF1h and DF2h denote 1 and 2 hours after receiving optical defocus, respectively. RE1h and RE2h denote 1 and 2 hours after removing the optical defocus, respectively. Data shown are in mean ± SEM, * p < 0.05, ** p < 0.01, two-way ANOVA.