Combined effects of atropine and myopic defocus against lens induced myopia in the chicks model

To study the dose-effect relationship of topical atropine against lens-induced myopia in chicks, and to determine whether combining atropine (ATR) and myopic defocus produce any additive effect. Myopia was induced in the right eyes of chicks using single power (-10D) or dual-power lenses (Plano/-10D and +10/-10D, area 50:50 ratio) while the left eyes were left untreated. In experiment I, a total of 60 chicks were randomly divided into six groups and received ATR eye drops of 5%, 3%, 1%, 0.1%, 0.01% or 0% (saline). In experiment II, 32 chicks were divided into four groups. Combination group received (1% ATR & +10/-10D), myopic defocus monotherapy group received (saline & +10/-10D), ATR monotherapy group received (1% ATR & plano/-10D) and control group received (saline & plano/-10D). Eye drops were administered once daily. Refractive error and biometry were measured by retinoscopy and A-scan ultrasonography respectively on days 0, 4, 8 and 12. Data are presented as mean interocular differences (IOD) ± standard deviation (SD). Experiment I: IOD in refractive error on day 12 were: Saline -11.05±1.41D vs 5% ATR: -6.25±2.77D, p< 0.0001; 3% ATR: -6.30±1.79D, p< 0.0001; 1% ATR: -6.10±1.79D, p< 0.0001; 0.1% ATR: -7.70±1.50D, p< 0.0001; and 0.01% ATR: -8.02±1.26D, p<0.0001; respectively, 2-way ANOVA. All tested concentrations of ATR showed reduced axial length elongation compared to the control group. Among all groups, 1% ATR was the most effectively. Experiment II: After 12 days, the ATR monotherapy group showed reduced myopic eye growth compared to the control (-9.25±1.11D vs -3.43±0.90D, p<0.0001). The myopic defocus monotherapy group and combination groups underwent hyperopic refractive shifts to the similar extent (6.87±2.20D vs 7.59±2.55D, p>0.80), suggesting that myopic defocus may have dominated the direction of growth and ATR provided no overall additional effect. Interestingly, we found that the combined treatment group showed a thicker choroid compared to the myopic defocus monotherapy group (64.66±13.68μm vs 49.08±9.08μm, p< 0.05), probably indicating a summation of growth signals at the intermediate stage of choroid. Daily application of ATR eye drop at 1%, 0.1% and 0.01% inhibited lens-induced myopia in chicks dose dependently. Combining 1% ATR with myopic defocus produced additive effect at choroid, but it was not reflected in axial length and refraction. This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.