Effects Of Different Monochromatic Lights On Eye Growth And Retinal-cones Distribution And Quantity In Guinea Pigs

PartⅠEffects of 430nm and 530nm monochromatic light on development of refraction and ocular dimensions in guinea pigsPURPOSE. To determine whether different colour visions produce predictable changes in refractive development and eye growth and characterize the properties of them by rearing guinea pigs in different monochromatic light for 20 weeks.METHODS. Thirty guinea pigs (two-weeks old) were randomly distributed to blue-light group (BL), green-light group (GL) and white-light group (WL) (n=10 for each group). In BL and GL group, guinea pigs were reared in monochromatic light of 430nm (blue) and 530nm (green) respectively. As to WL group, the animals were raised in white light as control. Another batch of forty guinea pigs were also randomly distributed to blue-white-light group (BWL), green-white-light group (GWL), blue-green-light group (BGL) and green-blue-light group (GBL) (n=10 for each group). For the BWL and BGL, the animals were initially reared in blue light for 10 weeks, then they were respectively transferred from blue to white or green light for another ten-weeks rearing continuously. It's similar for the GWL and GBL. The illuminative parameters of all groups were identical and the light quantum number was 3×10-4μmol·cm-2·s-1. All animals underwent biometric measurements including refraction, corneal curvature and axial length at each time-point (0,2,4,6,8,10,12, 14,16,18,20 weeks). The data from left eyes, not bilateral eyes, of all subjects were used for statistical analysis among groups in this study, so as to avoid the influence on statistics from the relationship between bilateral eyes. All these measurements were also statistically compared at each time-point between different groups and at different time-points within the same group (mixed model for repeated measures, Stata version 7.0). The inter-ocular difference and inter-group difference were defined as significant at p<0.05 and highly significant at p<0.01. RESULTS. There were no significant differences among groups in those biometric measurements obtained prior to exposure in different illumination (one way ANOVA: p>0.05).The refractions in different groups were significantly dependent on the spectral composition of the illumination. Eyes in GL group developed toward myopia accompany with a higher speed of vitreous extension after six-weeks illumination (P<0.01) when compared with WL group. However, eyes in BL group developed toward hyperopia accompany with a lower speed of vitreous extension after four-weeks illumination (P<0.001). Finally, the eyes of GL group (refraction was 0.90±0.61D, mean±S.D.) were induced maximum myopia (approximately 1.875D, p<0.001) versus WL group (refraction was 2.78±0.68D) after twenty-weeks illumination. In BL group (refraction was 6.95±1.25D), the eyes reached maximum hyperopia (approximately 4.175D,p<0.001) versus WL group at the end of illumination. The mean disparity between BL and GL group reached a maximum of 6.05D after twenty-weeks treatment, which was much greater than the longitudinal chromatic aberration (approximately 1.5D) between the blue and green light used here. There was no significant difference in radius of corneal curvature, depth of anterior chamber and lens thickness between the eyes of each group at any time-point (P>0.05).After ten-weeks exposure, all biometric parameters of BWL and BGL were similar to those of BL. And same for GWL and GBL to GL. After transferred to white light, the myopic refraction of GWL began to decrease, and then became stable at 20 week time point. But the refraction was still myopic, which was about-0.6 D, when compared with WL. After separated from blue light, the hyperopia of BWL also began to decrease, and then came to a stop at 20 week time point. But the refraction was still hyperopic, which was about+1.4D D, when compared with WL.After transferred to blue light, the myopic refraction of GBL began to decrease significantly, and vitreous lenghth of it stopped prolongation. At the end of the experiment, the refraction of GBL was+3.725±0.47D, and the vitreous lenghth of it was 3.39±0.07mm. When transferred to green light, the hyperopia of BGL also decreased rapidly and the speed of vitreous prolongation increased. At the terminal time point, the refraction of BGL was+3.325±0.50D, and the vitreous lenghth was 3.39±0.06mm. At this time, the refraction of WL was+2.78±0.68D, and the vitreous lenghth was 3.44±0.08mm. There was no significant difference in vitreous lenghth among GBL,BGL and WL group at the end of the experiment (P>0.05). CONCLUSIONS. Different colour visions can produce distinct and predictable changes in refractive development by influencing the axial growth of guinea pig, in which the most relative component is vitreous chamber. These results indicate that stimulating different types of cones by specific monochromatic light can lead to characteristic development in guinea pig eyes. That is, stimulating S-cones alone resulted in hyperopia and inversely solo excitation of M-cones leaded to myopia. PartⅡEffects of 430nm and 530nm monochromatic light on retinal-cones distribution and quantity in guinea pigsPURPOSE. To investigate retinal-cones distribution and quantity in guinea pigs reared in different monochromatic light for twelve weeks.METHODS. Thirty six guinea pigs (two-weeks old) were randomly distributed to blue-light group (BL), green-light group (GL) and white-light group (WL) (n=12 for each group). In BL and GL group, guinea pigs were reared in monochromatic light of 430nm (blue) and 530nm (green) respectively. The illuminative parameters of all groups were identical and the light quantum number was 3×10-4μmol·cm-2·s-1. All groups underwent biometric measurement including refraction, corneal curvature and axial length, etc. before and after twelve-week treatment. At the end of the observation, six guinea pigs of each group was used for retinal-cones immunocytochemistry, and another six of each group was used for flow cytometry of different retinal cones.RESULTS. There were no significant differences among groups in those biometric measurements obtained prior to exposure in different illumination (one way ANOVA: p>0.05). After twelve-weeks exposure, the eyes of GL group were induced myopia for about-1.5D (P<0.001), and about+3.2D hyperopia (P<0.001) was induced out in BL group. The result of retinal-cones immunocytochemistry indicated that, the density of M-cone in ventral retina of GL group increased(P<0.01), while the M-cone density in dorsal retina of BL group decreased(P<0.05). The S-cone density of BL retina increased significantly (P<0.05) in all the three zones, dorsal, central, ventral. But, the density of S-cone in GL group decreased with significant difference (P<0.01) in all over the three zones. The result from flow cytometry showed that 530nm monochromatic light induced increase of M-cone while decrease of S-cone, and 430nm monochromatic light resulted in M-cone's reduction but S-cone's increase.CONCLUSIONS.430nm and 530nm monochromatic light could influece the density of retinal-cones distribution and quantity in guinea pigs. It was indicated that all of the different cones may play a role in the development of this ametropia induced by monochromatic light.