Establishment of a Guinea Pig Model of Myopia Induced by Exposing to 530 nm Monochromatic Light / 中国实验动物学报

ABSTRACT

Objective In the early life period when eyes grow rapidly,visual experience can play an important role in axial growth and refractive development. For instance, depriving the eye of form vision during infancy will accelerate axial growth, resulting in substantial amounts of myopia, called form deprivation myopia (FDM). Similarly, imposing the eye with a negative lens produces compensating myopic growth in many species, called defocus induced myopia (DIM) . As one of the important visual experiences,color vision and its effects on eye growth deserve to be investigated. The purpose of this study was to investigate the effect of 530 nm monochromatic light and establish an innovative model of myopia in guinea pig by exposing to this monochromatic light. Methods Twenty male guinea pigs at 2 weeks old were randomly assigned to two groups (n = 10) . The experimental group was raised under the condition of 330 nm monochromatic light illumination. The control one was bred under white light illumination with 5000 k color temperature. These guinea pigs were raised in a specially designed cage. The light source was provided by specially made LEDs (green peak value 530 nm and half bandwidth 30 nm; white color temperature 5000 K) . The illumination parameters of the two groups were identical and the light quantum number was 3 x 10~(-4)μmol·cm~(-2)·s~(-1) . Through measuring,the irradiance value was 0.150 mW·cm~(-2) for green light and 0.247 mW·cm~(-2) for white light approximately. All animals were kept under a 12/12 h light/dark cycle (light 8 a.m. - 8 p.m. ) ,in the temperature of 22℃ - 26℃ and a relative humidity of 55% -65% . Both groups underwent biometric measurement including refraction,corneal curvature and axial length,etc. before and after twelve weeks treatment. The refraction was examined using a streak rednoscope and trial lenses in a dark room one hour after topically administering a cycloplegic eye drop. The radius of comeal curvature was measured with a keratometer (Topcon OM-4, Japan) and axial components was measured by A-scan ultrasonagraphy ( Opticon Hiscan A/B).Repeated measurements were undertaken. Only the right eye's parameters of each guinea pig were used for analysis. Unpaired (-tests were used in all comparisons between the two groups of eyes with a statistical analysis software (Stata, version 7.0) . Results Before treatment, the refraction of experimental group was 4.6 ± 0.59 D.and that of the control group was 4.63 ± 0.48 D. The axial and vitreous body length was 7.48 ±0.11 mm and 3.16 ±0.07 mm in the experimental group,respectively,and 7.55 ±0.16 mm,3.21 ±0.09 mm in the control. The differences between the biometric parameters of the two groups including refraction, comeal curvature and axial components were not significant ( P > 0.05) . However,after a twelve-week exposure, the variation of refraction in the experimental group was -3.125 ± 0.76 D,and - 1.075 ± 0.71 D was observed in the control group. There was a 2.0 D myopia in the experimental group compared with the control. Axial length grew 0.98 ± 0.13 mm in the experimental group and 0.77 ± 0.22 mm in the control. Vitreous body extended to 0.33 ± 0.14 mm and 0.13 ± 0.14 mm in the two groups, respectively. The refraction of the experimental group shifted more towards myopia ( P < 0.0001) accompanied with a more accelerated speed of axial growth and vitreous body's extension ( P < 0.05) compared with that of the control group. There were no significant differences in the radius of comeal curvature, the depth of anterior chamber and the lens thickness between the eyes of the two groups at the end of the experiment ( P > 0.05) . Conclusion The 530 run monochromatic light can accelerate the prolongation of axial length and vitreous body inducing axial myopia in guinea pigs.