| Objective:To investigate the refractive development and levels of Dopamine in guinea pigs under the conditions of varied light intensity(5Lux,500Lux, 10000Lux, white light, colour temperature 6000K)and the possible mechanism.Methods:Thirty guinea pigs at 3 weeks old were randomly assigned into three groups, the high light intensity group(n=10), the normal control group(n=10), and the low light intensity group(n=10), which were raised under the light illumination of 10000 lux,5001ux and 51ux with 6000 k color temperature respectively from 6:00 am to 6:00 pm。The refractive power, the radius of corneal curvature and axial length (AL) of the right eyes were measured by a streak retinoscopy, keratometer (Topcon OM-4, Japan) and A-scan ultrasonagraphy (Opticon Hiscan A/B) respectively before and after 12 weeks of treatment. After 12 weeks of light exposure, guinea pigs in each group were killed for light microscopy and electron microscope examination. HPLC was also conducted. One-way analysis of variance (ANOVA) was used in all comparisons between the three groups of eyes with a statistical analysis software (SPSS 10.0).Results:There were no significant differences among groups before the experiment((P>0.05). After 12 weeks of treatment, the variation of refraction in the high light intensity group was 0.45±1.65D, and 2.28±0.66D was observed in the control group.the refraction of the high light intensity group became more hyperopic compared to the control group (4.03±1.59D versus 2.15+2.01D, P<0.05). There was about 1.50D hyperopia shift in the high light intensity group compared with the control group. Axial length increased 0.54±0.10mm in the high light intensity group and 0.76±0.05mm in the control group. The high light intensity group accompanied with a less accelerated speed of axial growth compared with that of the control group (P<0.05). The radius of corneal curvature increased in all groups among the eyes of the three groups at the end of the experiment, but there were no significant differences (P>0.05). The levels of Dopamine in the high light intensity group were much more than that in control group ((148.70±22.44 nmol/g versus 44.50±12.45 nmol/g, P<0.01). There was no difference between the low light intensity group and the control group in refraction, the radius of corneal curvature and the levels of Dopamine after 12 weeks of light exposure(P>0.05). The thickness of the sclera at the posterior pole in the high light intensity group increased compared to that in the control group. Under electron microscopy, the space of membrane disc widened in part of the photoreceptor outer segments in the high light intensity, and swelling of mitochondrial and loss of cristae in part of the the photoreceptor inner segments were also observed. Nothing abnormal was detected for the rest.Conclusion:High light intensity can slow the growth of the axial length and emmetropization process in guinea pigs, while low light intensity makes no difference to the normal eye development of the guinea pigs. The levels of Dopamine can be increased on the condition of high light intensity, which may partly explain the change of the eye development. High light intensity may cause slight injury to the retina photoreceptors of guinea pigs. |
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