Contributions from light level and spectral content on refractive development in young rabbits

Abstract

Aim: To compare the effects of manipulating light levels versus manipulating the spectral content of short wavelengths (blue light) of ambient lighting on refractive development in young rabbits.

Methods: A total of 32 healthy 3-week-old rabbits were randomly assigned to one of the four groups with 8 in each group for 12wk: Control group (NC) under low blue light (output ratio of blue light 1.8%) at low illuminance (341 lx), HI group under low blue light (output ratio of blue light 1.6%) at high illuminance (5057 lx), simulating natural light (S-NL) group under high blue light (output ratio of blue light 4.9%) at high illuminance (5052 lx), and MB group under high blue light (output ratio of blue light 5.2%) at low illuminance (342 lx). The lighting in each group were provided by light emitting diode (LED) lamps emitting visible light (range 380-780 nm) in addition to (or not) LED lamps only emitting short wavelength (range 380-500 nm). Refraction, axial length, and corneal curvature radius were assessed by retinoscopy, ultrasonography and keratometry, respectively. Average data of both eyes for each animal were used as single values and compared among groups.

Results: During the 12-week intervention, all animals had an emmetropization period. The decrease of refraction in rabbits in HI group was similar to S-NL group, both slower than that of NC group (P<0.001). At the 12^th week, the refraction (3.000±0.267 D) and vitreous cavity depth (7.421±0.168 mm) of S-NL was similar to HI group (3.250±0.267 D, 7.264±0.256 mm), significantly different from NC group (1.937±0.291 D, 7.825±0.313 mm; P<0.001 for both). High blue light at low illuminance had little effect on refraction change. At the end of intervention, the difference of refraction (2.219±0.281 D) and vitreous cavity depth (7.785±0.229 mm) in MB group were not statistically significant (P=0.311, P=0.749) compared with NC group. The other components were less affected by lighting conditions (P>0.05).

Conclusion: The light levels per se but not the rich in spectral content of short wavelengths determine the inhibitory effect of ambient lighting on myopia development in rabbits.

Keywords: emmetropization; illuminance; myopia; refractive error; short wavelengths.

Figure 1. Relative spectral distribution of light conditions

A, C: Spectral distribution of less blue light at low illuminance and less blue light at high illuminance were the same. The proportion of short-wavelength light with wavelength below 500 nm was small. B: The spectral distribution of more blue light at high illuminance. The relative power ratio of short wavelengths with wavelength below 500 nm were higher than that of the control group. D: The spectral distribution of more blue light at low illuminance. The relative power ratio of short wavelengths with wavelength below 500 nm were similar to more blue light at high illuminance, significantly higher than control group and less blue light at high illuminance group.

Figure 2. Refractive development in young rabbit over 12wk

During the intervention, all rabbits had an emmetropization period with the decreasing of hyperopia. A: Refractive response of animals in NC group; B: Refraction of 8 young rabbits raised in HI group was higher hyperopia than that of animals raised in NC group; C: Refraction in MB group was closer to NC group; D: Refraction of animals in S-NL group was higher than NC group. NC: Less blue light at low illuminance group; MB: More blue light at low illuminance group; HI: Less blue light at high illuminance group; S-NL: More blue light at high illuminance group.

Figure 3. Changes in refraction and axial components

A: Myopia change in HI group was similar to S-NL group, significantly lower than that in NC group; B: Vitreous cavity elongation in HI group was similar to S-NL group, significantly lower than that in NC group. Values are the average of the right and left eyes. ^aP<0.001 compared with NC group, LSD-t test. NC: Less blue light at low illuminance group; MB: More blue light at low illuminance group; HI: Less blue light at high illuminance group; S-NL: More blue light at high illuminance group.

Figure 4. Association between the change in refraction and ocular components

Values are the average of the right and left eyes. NC: Less blue light at low illuminance group (black); MB: More blue light at low illuminance group (blue); HI: Less blue light at high illuminance group (red); S-NL: More blue light at high illuminance group (yellow).

Figure 5. Changes of eye parameters grouped by blue light and illuminance

A, B: There were no significant difference between the changes in refraction and axial components in less or more content of short wavelengths; C, D: High illuminance lighting significantly inhibited the changes in refraction and vitreous cavity depth, and the changes were significantly lower than that in low illuminance. ^aP<0.05 independent t-test.