The Effect of Different Wave Lengths of Monochromatic Light on the Refraction, Axial Length and Blood Melatonin Levels in Rats

Abstract

Purpose:: To find out the effect of different wave lights on the refractive development of rats and to assess whether melatonin have an effect in controlling emmetropisation.

Methods:: Three generation male Sprague-Dawley rats comprised the study group. They were divided into 5 groups regarding to exposure of monochromatic light as follows: Group 1 (control) (n=10) was exposed to daylight, Group 2 (n=10) was kept consistently in dark, Group 3 (n=10) was exposed to red light (670 nm) for 8 hours a day and kept in the dark for the remaining 16 hours, Group 4 (n=10) was exposed to yellow light (570 nm) for 8 hours a day and kept in the dark for the remaining 16 hours, Group 5 (n=10) was exposed to blue light (450 nm) for 8 hours a day and kept in the dark for the remaining 16 hours. The third generation born male rats were used in the experiment. The beginning of the gestation period was marked as day 0. Blood samples for melatonin level were obtained when the rats were 6 months old. All blood samples were taken at the third hour of the dark cycle. After finishing the study protocol retinoscopy and axial length measurements were performed.

Results:: There was no statistically significant difference in terms of axial lengths and refractive errors in neither group. Blood melatonin level of the rats who have been kept in dark (group 2) and exposed to red light (group 3) and yellow light (group 4) was found to be significantly lower when compared to that of the control group (group 1) and exposed to blue light (group 5). There was no statistically significant relationship between the axial length, refraction and blood melatonin levels.

Conclusions:: Monochromatic wavelights and darkness have no considerable effect on ocular refraction and axial length in the subsequent generations. Blood melatonin level seems to have no significant role in the development of the rat’s refraction and axial length.

Keywords: emmetropization • melatonin • refraction