Short Wavelength (Blue) Light Is Protective for Lens-Induced Myopia in Guinea Pigs Potentially Through a Retinoic Acid-Related Mechanism

Abstract

Purpose: To investigate the effect of short-wavelength light (SL) on guinea pigs with lens-induced myopia (LIM) and the possible retinoic acid (RA)-related mechanisms.

Methods: Two-week-old guinea pigs (n = 60) with monocular -5D lenses were reared under white light (WL, 580 lux) or SL (440 nm, 500 lux). The left eyes were uncovered as control. Refractive error (RE) and axial length (AL) were measured at baseline, one week, two weeks, and four weeks after intervention. Retinal RA was measured from four guinea pigs after two and four weeks of treatment with HPLC. Two-week-old guinea pigs (n = 52) with monocular -5D lens were fed with either RA or its synthesis inhibitor citral every third day in the morning, and half from each group were reared under WL or SL conditions. RE and AL were recorded at baseline and two and four weeks after intervention. Retinal RA was measured after four weeks of intervention.

Results: At the end of treatment, guinea pigs exposed to SL were less myopic than to WL (2.06 ± 1.69D vs. -1.00 ± 1.88D), accompanied with shorter AL (P = 0.01) and less retinal RA (P = 0.02). SL reduced retinal RA even after exogenous RA supplementation (P = 0.02) and decelerated LIM compared to WL (1.66 ± 1.03D vs. -3.53 ± 0.90D). Citral slowed ocular growth, leading to similar RE in W+CI and S+CI groups (3.39 ± 1.65D vs. 5.25 ± 0.80D).

Conclusions: Overall, SL reduced LIM in guinea pigs, even in those supplemented with oral RA, accompanied by reduced retinal RA levels. Oral RA accelerated eye elongation, but citral equally decelerated eye elongation under SL and WL with no significant retinal RA reduction.

Figure 1.

Biometric parameters (Mean± SEM), including (A) refractive error (Diopter, D), (B) vitreous chamber depth (mm), and (C) axial length (mm) of treated (solid lines) and fellow (dashed lines) eyes plotted against treatment time (weeks) in guinea pigs wearing monocular −5D lenses (treated eyes) reared under white light (WL, black lines) or short-wavelength light (SL, blue lines) conditions. Asterisks refer to the significant difference between guinea pigs under WL or SL conditions. *P < 0.05, **P < 0.01, ***P < 0.001. n = 26 across all treatment time.

Figure 2.

Linear regression of change in refractive error (change in RE) and change in axial length (change in AL) after four-week treatment period, in guinea pigs reared under white light (WL, black circle/line) or short wavelength light (SL, blue box/line). Open circles/boxes represent fellow eyes, closed circles/boxes represent treated (wearing −5D lens) eyes. The line is fitted to both lens defocus and fellow eyes. AL changed in parallel with a change in RE in both groups (P < 0.001).

Figure 3.

Retinal retinoic acid level (RA concentration/weight of retina, µg/g) in guinea pigs reared under short wavelength or white light conditions at two weeks (A) and four weeks (B) after monocular lens treatment. Each black circle represent RA level from each guinea pig under white light; each blue triangle represents RA level from each guinea pig under short wavelength light. Closed symbols represent RA level from lens treated eyes, open symbols represent RA level from fellow eyes. Error bars denote SD. Treated: eyes with −5D lens wearing; fellow: left eyes set as control. P values calculated by Mann-Whitney U test are presented above the corresponding bars.

Figure 4.

Biometric parameters between guinea pigs fed with retinoic acid (Left column, A, B, C) or fed with citral (Right column, D, E, F) under white and short wavelength light conditions: Mean ± SEM values in A and D, refractive error in D, vitreous chamber depth (mm) in B and E, and axial length (mm) in C and F of treated (solid lines) and fellow (dashed lines) eyes plotted against treatment time (weeks) in guinea pigs wearing monocular −5D lenses (treated) reared under WL (black lines) or SL (blue lines) conditions. Asterisks refer to the significant difference between guinea pigs under WL or SL conditions. * P < 0.05, ** P < 0.01, *** P < 0.001.

Figure 5.

Linear regression of change in refractive error (change in RE) and change in axial length (change in AL) during the four-week treatment period, in guinea pigs fed with RA (A) or citral (B) and reared under white light (black circle/line) or short-wavelength light (blue box/line). The line is fitted to both the lens defocus and fellow eye. Closed circles/boxes represent treated eyes, open circles/boxes represent fellow eyes. AL changed in parallel with a change in RE in all groups (P < 0.05).

Figure 6.

Retinal retinoic acid level (RA concentration/weight of retina, ug/g) between guinea pigs fed with retinoic acid (A) or fed with citral (B) reared under white (A, W+RA; B, W+CI) or short-wavelength light (A, S+RA; B, S+CI) conditions four weeks after monocular lens treatment. Error bars denote SD. Each white circle represent RA levels from each guinea pig under white light; each blue triangle represent RA levels from each guinea pig under SL. Closed symbols: treated eyes with −5D lens wearing; open symbols: fellow eyes set as control. P values calculated by Mann-Whitney U test were distributed above the corresponding bars.