Abstract
Purpose :
This study investigated the effects of daily short-term myopic defocus of varying amount and duration on myopia progression in chicks.
Methods :
The chicks were raised under a 12h light/12h dark cycle. 7-day-old chicks wore a monocular -5D lens for 1 week (days 1-7) as “pre-treatment” to induce myopia, after which they were split into groups. The chicks were exposed during the day to 1 of 5 treatments for 4 days (days 8-11): -5D12h (control, -5D/12h), -5D8h/-1D4h (-1D/4h), -5D4h/-1D8h (-1D/8h), -5D8h/-3D4h (-3D/4h) and -5D4h/-3D8h (-3D/8h). The contralateral eyes served as controls. Refractive errors (RE) and ocular dimensions were measured using retinoscopy and high-frequency A-scan ultrasonography, at baseline and on days 4, 7, 9 and 11 of pre-treatment and treatment periods.
Results :
The -5D lenses induced myopic shifts in treated eyes relative to their fellows after 7 days (-4.86 ±0.16 D, n=37, p<0.001), coupled to an increase in axial length (AL, anterior cornea to inner sclera distance: 0.25 ± 0.02 mm, p<0.001) and vitreous chamber depth (VCD: 0.23 ±0.01 mm, p<0.001). From day 8 to 11, daily switching from a -5D lens to either a -3D or -1D lens in the afternoon for 4 or 8 h slowed or totally inhibited myopia progression (Fig. 1). Specifically, interocular differences in REs on day 11 for the -5D/12h group was -4.15 ±0.44 D (n= 7), compared to -1.04 ±0.24 D (-1D/4h: n=7, p<0.001), -1.98 ±0.24 D (-1D/8h: n=8, p<0.05), -3.04 ±0.49 D (-3D/4h: n= 7, NS), and -3.75 ±0.56 D (-3D/8h: n=8, NS). The -1D/4h afternoon treatment abolished the interocular difference in AL by day 11 (0.002 ± 0.03 mm, p<0.01), with the 3 other treatments slowing axial elongation, thereby reducing interocular differences in AL, i.e., 0.10 ±0.06 mm (-1D/8h: NS), 0.11 ±0.07 mm (-3D/4h: NS) and 0.21 ±0.5 mm (-3D/8h: NS), compared to 0.29 ±0.03 mm (control). Interocular differences in VCD showed similar trends to interocular differences in AL.
Conclusions :
Daily, limited exposure to myopic defocus proved to strongly influence myopia progression in adolescent chicks, with higher magnitudes achieving greater slowing of myopia progression, even with short durations. If translatable to humans, the results of this study open up novel treatment strategies for clinical myopia control.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.