The Effect Of Chromatic Stimulus On Scleral Remodeling Regulated Eye Growth In Guinea Pigs And Accommodative System In Human

Part?Effects of chromatic stimulus on scleral remolding and eye growth in guinea pigsSection IEffects of chromatic stimulus on refractive development and choroidal and scleral morphological changes in guinea pigsPurpose:To investigate the effects of 430nm and 530nm monochromatic lights on the refractive state and chroidal and scleral morphological changes in guinea pigs.Methods:Thirty pigmented guinea pigs (2-3 weeks old) were randomly divided into three groups:530nm monochromatic light,430nm monochromatic light and white light (color tempterature of 5000K). The light quantum number of illumination was identical for the three different lights. Animas were kept under a 12/12h light/dark cycle. Optical and biometric measurements were conducted before, four weeks and eight weeks after treatment. At the end of the experiment, five animals of each group were terminated and the eyeball was enucleated and examined with light microscopy and transmission electron microscope. Repeated measures analysis of variance were used for data analysis and difference was defined as significant at P<0.05.Results:1) After 4 weeks of treatment, the mean refraction of the 530nm light group changed toward more myopic of-0.08±0.41D (P=0.725) comparing with that of white light group, while the 430nm group developed toward more hyperopic of 1.72±0.78D (P<0.001) than that of white light group. After 8 weeks, the mean refraction for the 530nm light group reached more myopic of-1.20±0.40D (P<0.001) and that for the 430nm group reached more hyperopic of 2.15±0.87D (P<0.001) comparing with the white group.2) For the biometric measurements, the vitreous length changed differently in three groups with treatment time. After 4 weeks of treatment, an increase in vitreous length of 0.15±0.08mm was found for the 530nm group, about 0.05±0.12mm (P=0.326) more than white light group. In the 430nm group, vitrous length increased of 0.02±0.05mm, about 0.09±0.07mm (P=0.056) less than white light group. And after 8 weeks of treatment, the differences of vitreous lengths between the monochromatic light groups and the white light group became significant. The 530nm group had more increase of 0.12±0.11 mm (P=0.036), while 430nm group had less increase of 0.11±0.08 mm (P=0.006) comparing with the white light group. The anterior segment and lens thickness increased with treatment, but no significant inter-group differences were observed at follow-up time points (P>0.05) 3) After 8 weeks of treatment, the scleral collagen fibril morphology was found to be altered, and fibroblasts were in a relatively quiescent state in 530nm light group. On the contrast,430nm light group had normal scleral collagen fibril morphology.4) The choroidal thicknesses of 530nm light group,430nm light group and white light group were 40.15±10.12?m,41.71±8.2?m and 41.29±9.7?m without significant differences. The posterior scleral thickness of 530nm group was significantly thinner than the white light group (93.91±7.1?m vs.97.46±12.3?m, P= 0.008), while that of 430nm group was not significantly different from white light group (101.32±10.2?m vs.97.46±12.3?m, P=0.057).Conclusions:The results suggest that different chromatic stimulus contributes to the refractive development of guinea pigs. Long-wavelength monochromatic light (530nm) can induce relative myopia, while short-wavelength monochromatic light (430nm) can induce relative hyperopia, which primarily result from the changes of eye growth rate. Long-wavelength monochromatic light (530nm) results in thinning in the sclera, while short-wavelength monochromatic light (430nm) has no obvious difference in the scleral thickness compared with the white light. Futher study on the effects of chromatic stimulus on the scleral characteristics is warrant.Section?Effects of chromatic stimulus on scleral biomechanical properites and scleral tissue remodeling in guinea pigsPurpose:To evaluate the effects of 430nm and 530nm monochromatic lights on scleral biomechanical properties and scleral tissue remodeling in guinea pigs.Methods:At the treatment period of four weeks and eight weeks, eyes of animals in each groups were enucleated and residual orbital tissue carefully removed. For creep measurement,2-mm wide by 6-mm long scleral samples were cut crossing the posterior pole of the eye in the inferior-superior direction approximately 2mm from the optic nerve head. CMT 6000 testing system (MTS System Corporation, USA) was used to apply controlled amounts of tension to the sclera samples and to measure the elongation. After preload test, the creep behavior of scleral samples was studied under the load condition of 0.05N for 20 minutes. Creep extension (200-800 seconds) was computed as a percentage of the length change. Also, RT-PCR was used to measure levels of mRNA for collagen (?1(?) chain), aggrecan, MMP-2 and TIMP-2. Meanwhile, western-blot was applied to evaluate the expression of collagen (?) and aggrecan. ANOVA was used for analysis and P<0.05 was considered significantly different.Results:1) The creep test results showed that creep extension of scleral samples from the 530nm group was greater than that from the white light group after 4 weeks (P=0.01) and 8 weeks (P=0.042); while the creep extension from the the 430nm group was smaller after 4 weeks (P=0.021), and was not significantly different comparing with the white light group afte 8 weeks (P=0.067).2) Results from RT-PCR showed that comparing with white light group, the expression of?1(?) collagen was lower for 530nm group after treatment (4w, P=0.023; 8w, P=0.048), but was not significantly different for 430nm group (4w, P=0.927,8w, P=0.910). The expression of aggrecan was also lower for 530nm group (P=0.037, P=0.015) than white light group, while for the 430nm group, it was higher after 4 weeks (P=0.047) and similar to the white light group after 8 weeks (P=0.210). As for the MMP-2 level, it was upregulated for 530nm group after 4 weeks (P=0.007) and showed no obvious difference after 8 weeks (P=0.815). There were no significant differences between 430nm group and the white light group (4w, P=0.947; 8w, P=0.510). The expression levels of TIMP-2 showed no significant changes for both 530nm group (4w, P=0.524; 8w, P=0.072) and 430nm group (4w, P=0.375; 8w, P=0.810) comparing with the white light group.3) The results of collagen I and aggrecan from western blot were consistent with those from RT-PCR.Conclusions:Chromatic stimulus induces the scleral biomechanical properties alternations. After exposure to 530nm monochromatic wavelength light, the sclera becomes more extensible than 430nm monochromatic wavelength light and the white light. Besides, the scleral extracellular matrix changes due to the chromatic stimulus. 530nm monochromatic wavelength light decreases the expression of collagen I and aggrecan, while upregulates the MMP-2 expression. The mechanism of chromatic stimulus on regulating the scleral tissue remodeling in guinea pigs remains to be further investigated. Part?The effects of chromatic stimulus on near accommodative response and blur sensitivityPurpose:To investigate whether different chromatic stimuli of colored targets have impact on the stability and blur sensitivity of near steady-state accommodative functions.Methods:Twelve individuals aged between 20 years and 30 years (mean,25.5±3.4 yeares) were included in the study. All the subjects had refractive error less than-6.00D and a better UCVA than 20/20. And they had normal binocular vision and normal color vision. Informed consent was provided by all the participants. They had soft contact lenses to correct the refractive error within±0.25 D in their tested right eyes.The target was presented with the Badal system. A 3×3 array of colored Snellen E letters with spatial frequency of 12 c/deg was used as fixation target. According to the 1931CIE-XYZ Color System, three target-on-background color combinations were used:black on white, red on green and blue on yellow. The dominant wavelengths of blue and red are 440nm and 650nm, and the dominant wavelengths of yellow and green are 580nm and 510nm. The luminances of three targets were kept the same. The subjects were instructed to look at the three targets in a randomized order and keep them clear. The accommodative stimulus (AS) was presented using a Badal stimulator and the accommodative responses (AR) were measured using an open-field infrared autorefractor (Grand Seiko WAM 5500) at a sampling rate of 5 Hz. The AR was measured at 3D AS levels. The accommodative microfluctuations were measured for 20 sec at one time. The root mean square value (r.m.s.) was calculated to represent the magnitude of accommodative microfluctuations. To measure the objective blur threshold, the AS was changed by 0.1 D step using Badal system while the AR was continuously recorded. Objective blur threshold was determined by the least dioptric vergence that could cause a statistically detectable change in the AR. Repeated measures ANOVA were conducted to analyze the data. P<0.05 was considered stastically significant.Results:1) At the 3D AS level, the AR to black-on-white target, blue-on-yellow target and red-on-green target were 2.37±0.18D,2.06±0.20D,2.16±0.21D, respectively. The AR to black-on-white target was significantly larger than that to red-on-green target (P=0.044) and blue-on-yellow target (P=0.010). And AR to red-on-green target was 0.11±0.03 D larger than that to blue-on-yellow target (P =0.008).2) At the 3D AS level, the r.m.s. values of the accommodative microfluctuations to black-on-white target, blue-on-yellow target and red-on-green target were 0.173±0.027D,0.164±0.035D,0.206±0.014D, respectively. There were not significant differences between black-on-white target and blue-on-yellow target (P=0.171). The magnitude of accommodative microfluctuations to red-on-green targer was larger than that to black-on-white target (P=0.025) and blue-on-yellow target (P=0.021).3) At the 3D AS level, the objective blur threshold to black-on-white target, blue-on-yellow target and red-on-green target were 0.135±0.023D,0.133±0.041D,0.203±0.050D. There were not significant differences between black-on-white target and blue-on-yellow target (P=0.836). The object of blur threshold to red-on-green targer was larger than that to black-on-white target (P =0.030) and blue-on-yellow target (P=0.028)Conclusions:The accommodative system has lower blur sensitivity and stability to the red-on-green target than black-on-white and blue-on-yellow targets. Chromatic stimulus can affect the accommodative responses as well as stability and blur sensitivity of accommodative system. The effects of colored target on the magnitude of accommodative microfluctuations and the objective blur threshold were consistent. S cone and chromatic signal may have a role in this effect.