Abstract:  Objective To observe the effects of monochromatic lights with similar luminance on the preditable changes in eye growth and expression of  vasoactive intestinal polypeptide (VIP) in guinea pigs and to discuss the relative mechanism. Design Experimental study. Participants Thirty-six 1 week old British species of tri-color male guinea pigs. Method 36 guinea pigs were randomly divided into A, B and C groups, each with 12, which were respectively raised in red light (610 nm, long wave-length), bule  light (430 nm, short wave-length) and white light (broad spectrum) with same luminance (200 lux). At the time of 0 w, 3 w and 6 w of experiment, refraction and axial length were measured. Besides, 4 guinea pigs of each groups were randomly selected to be removed eyes at the 6th w. The eyes removed were fixed 48 h in 4% Paraformaldehyde phosphate buffer solution, and then separated sclera from retina and choroids. Calculated dry weight of sclera obtained. While the left retina tissues were made into paraffin sections to HE staining and detect expression of VIP with immunohistochemistry (SP three steps). Main Outcome Measures  Refraction, axial length, dry weight of sclera, counts of retina VIP-immunoreactive cells and the value of retina VIP integrated optical density(IOD).  Results  At the end of study, refraction of red, blue, and white light groups was respectively 2.696±0.171 D， 5.139±0.151 D, and 3.161±0.122 D (F=605.169，P=0.000）, whereas the corresponding axial length of three groups was repectively 8.273±0.165 mm, 8.019±0.151 mm, and  8.161±0.120 mm （F=6.009，P=0.009）. Average dry weight of sclera in each group was 0.609±0.088 mg，0.716±0.101 mg, and 0.680±0.041 mg with no statistic difference （F=2.292，P=0.126） yet, there was a significant variation between that of Group A and Group B (F=1.256，P=0.048）. VIP was most expressed in inner plexiform layer , ganglion cell layer and nerve fiber layer of retina, with scattered expressed in inner nuclear layer and photoreceptor cells layer. In addition, the expression of VIP in retina was most in Group A, the number of retina VIP-immunoreactive cells and the value of retina VIP IOD were respectively 43.250±9.939 and 1.622±0.119; while that was least in Group B, corresponding results of the two measurements mentioned above were 27.500±4.928 and 1.273±0.127 respectively. There existed great difference among three groups (F=8.478, 5.082; P=0.002, 0.000).  Conclusions Red light(long wave-length) could promote eye growth and myopia occurrence, while blue light (short wave-length) was on the opponent. VIP, a potential signal molecular, may be involved in the regulation of monochromatic lights on eye growth, by affecting scleral metabolism and morphological structure.

Key words: monochromatic lights , myopia, vasoactive intestinal polypeptide (VIP) , sclera , guinea pig