Low, W. Y. S. | bioRxiv Science

bioRxiv2022

A duration-dependent interaction between high-intensity light and optical refocus in the drive for myopia control

PURPOSETo evaluate the duration-dependent and synergetic impact of high-intensity light (HL) and optical refocus (RF) on lens-induced myopia (LIM) development in chickens. METHODSMyopia was induced in one eye in chicks (10 groups, n=126) from day 1 post- hatching (D1) until D8 using -10D lenses. Fellow eyes remained uncovered as controls. Nine groups were exposed daily to continuous 2 hours (h), 4h, or 6h of either HL (15,000 lux); RF (removal of -10D lens); or both (HL+RF). One group served as the LIM group without any interventions. Ocular axial length (AL), refractive error, and choroidal thickness were measured on D1, D4, and D8. Outcome measures are expressed as inter-ocular difference (IOD= experimental - control eye) {+/-}SEM. RESULTSBy D8, LIM increased AL (0.36{+/-}0.04 mm), myopic refraction (-9.02{+/-}0.37D), and choroidal thinning (-90.27{+/-}16.44 {micro}m) in the LIM group (all, P<0.001). Compared to the LIM group, exposure to 2h, 4h, or 6h of HL, RF, or HL+RF reduced myopic refraction in a duration-dependent manner, with RF being more effective than HL (P<0.05). Only 6h of HL+RF (not 2h or 4h) prevented LIM and was more effective than RF (P=0.004) or HL (P<0.001) in reducing myopic refraction, and more effective than HL (P<0.001) in reducing axial elongation. CONCLUSIONDaily exposure to 2h, 4h, or 6h of HL, RF, or HL+RF reduced lens-induced myopic refraction in a duration-dependent manner in chickens. Only 6h of HL+RF completely stopped LIM development. The synergetic effect of HL and RF is dependent on the duration of the interventions.

neuroscience↗

bioRxiv2021

Recovery from form-deprivation myopia in chicks is dependent upon the fullness and correlated colour temperature of the light spectrum

BackgroundTo evaluate the impact of full-spectrum light-emitting diodes (LEDs) mimicking sunlight on ocular axial elongation and refractive error development in a chicken model of myopia. MethodsA total of 39 chicks (Lohmann brown), 1 day-old, were randomly distributed into 3 groups. Animals were housed for 28 days in a temperature-controlled enclosure, under a 12/12h light/dark cycle of isoluminant ([~]285 Lux) fluorescent [n = 18, (4000K, FL-4000)] or Sunlike-LED [n=12, (4000K, SL-4000); n = 9, (6500K, SL-6500)] white lights. Myopia was induced monocularly in all chicks by random occlusion of one eye with a frosted diffuser, from day 1 post-hatching (D1) until D14. On D14, diffusers were removed, and recovery from myopia was monitored under the same experimental light condition. Axial length (AL), refractive status, choroidal thickness and anterior chamber depth were recorded on days 1, 7, 14, 22 and 28. Ex vivo scleral collagen fibre thicknesses were measured from scanning electron microscopy images. Differences in outcome measures between eyes and groups were compared using 2-way repeated-measures ANOVA. ResultsThere was no significant difference between groups in the AL and refraction of form-deprived (FD) eyes during form-deprivation (D1 to D14). FD eyes of animals raised under SL-4000 and SL-6500 recovered more rapidly from excessive axial elongation than those of animals raised under FL-4000, by D22 and D28. Correspondingly, the refractive status of FD eyes exposed to SL-4000 and SL-6500 was close to that of control eyes by D28. The choroid became thicker during recovery in FD eyes compared to control eyes, in all groups. Choroidal thickness was significantly greater in FD eyes of chickens raised under SL-6500 than in animals raised under FL-4000 (P < 0.01). The diameter of scleral collagen fibrils was significantly greater in recovering FD eyes of chickens raised under SL-6500, than in those raised under FL-4000 (P = 0.04) and SL-4000 (P = 0.002). ConclusionsCompared to fluorescent light, moderate intensities of full-spectrum Sunlike-LEDs can accelerate recovery from form-deprivation myopia in chickens, potentially through choroid-mediated pathways increasing the diameter of scleral collagen fibrils. This study highlights an important implication of the spectral content of white light on ocular growth and emmetropization.

neuroscience↗