Correlation between light levels and the development of deprivation myopia.

PURPOSE: In chicks, daily exposure to bright light (15,000 lux) retards the development of form-deprivation myopia (FDM) by roughly 60%. This study investigated whether higher light intensities increase the amount of protection against FDM, and whether protection and light intensity are correlated. Furthermore, we examined if exposure to bright light can prevent the progression of FDM or whether it affects only the onset of experimental myopia. METHODS: Experiment 1: Chicks wore translucent diffusers monocularly for a period of 7 days, with exposure to one of five light intensities (500, 10,000, 20,000, 30,000, and 40,000 lux, n = 12 per group). Experiment 2: Chickens wore translucent diffusers monocularly for 11 days and were split into three groups: (1) chicks reared under 500 lux, (2) chicks reared under 40,000 lux, and (3) chicks reared under 500 lux for the first 4 days and 40,000 lux for the remaining 7 days. RESULTS: A significant correlation was observed between log light intensity and the development of FDM, with a lesser myopic refraction (F (28, 330) = 60.86, P < 0.0001) and shorter axial length (F (4, 20) = 8.87, P < 0.0001) seen with increasing light intensities. The progression of FDM was halted in chicks that were switched from 500 to 40,000 lux. CONCLUSIONS: The level of protection from the development of FDM increases with increasing light intensity. Daily exposure to 40,000 lux almost completely prevents the onset of FDM and, once myopia is established, halts further progression.

Gene expression within the amacrine cell layer of chicks after myopic and hyperopic defocus.

PURPOSE. Ocular growth is regulated locally by signals produced in the retina. The highly heterogeneous nature of the retina may mask important changes in gene expression during global analysis. This study was conducted to investigate changes in gene expression specifically within the amacrine cell layer (ACL), the most likely generator of growth signals, during optical manipulation of ocular growth. METHOD. Chicks were monocularly treated with either -7-D (n = 6) or +7-D (n = 6) lenses for 24 hours. Untreated age-matched chicks served as control subjects (n = 6). Total RNA from the ACL was isolated from 10-mum-thick sections, obtained using laser capture microdissection. Labeled cRNA was prepared from three samples per condition and hybridized to chicken genome microarrays. Changes in gene expression were validated by using semiquantitative real-time RT-PCR. RESULTS. One hundred twenty-eight genes were differentially expressed in the ACL of the minus lens-treated eyes, whereas the plus lens-treated eyes displayed 58 changes 24 hours after treatment. Only 11 genes were differentially expressed under both experimental conditions, whereas the expression of only one gene (clone ChEST927g14) was modulated by the sign of defocus. Compared with previous studies in the field, the magnitude of changes observed in the present work were larger, with more than 30% of differentially expressed genes showing a twofold or greater modulation in expression. The results, obtained from independent validation by real-time RT-PCR technology, correlated highly with the original microarray data. The differential expression of four of eight genes was validated in plus lens-treated eyes, and eight of nine genes were independently validated in minus lens-treated eyes. CONCLUSIONS. The targeted investigation of the ACL enabled the identification of several novel genes that may form part of the growth regulatory pathways of the eye. Different retinal pathways may underlie the response of the eyes to plus and minus lens compensation, as there was limited overlap in the regulated genes observed within the ACL under both conditions.