Effects of 7-methylxanthine on the sclera in form deprivation myopia in guinea pigs.

The aim of this study was to determine the effect of the adenosine receptor antagonist 7-methylxanthine (7-MX) on form deprivation myopia in 3-week-old guinea pigs. Two groups of 3-week-old guinea pigs were subjected to monocular deprivation (MD) using a diffuser and fed either 7-MX (300 mg/kg body weight; n = 7) or vehicle control (saline at an equal volume to 7-MX; n = 7). A control group (n = 6) was not subjected to form deprivation. Ocular refraction, axial length and body weight were measured at the start and after 21 days. The thickness of the posterior sclera was measured by light microscopy and the collagen fibril diameter in the inner, middle and outer layers of the sclera was measured by electron microscopy. In the vehicle control group, 21 days of MD produced significant amounts of myopia, axial elongation, thinning of the posterior sclera and thinning of the median collagen fibril diameter in the posterior sclera relative to the contralateral eyes. In the guinea pigs fed with 7-MX, however, form deprivation produced significantly less myopia and axial elongation compared with vehicle control animals. The 7-MX-treated animals exhibited a thickening of the posterior sclera in both the MD eye and the contralateral eye. In the 7-MX-treated animals, the median collagen fibril diameter in the posterior sclera was not reduced by form deprivation. Treatment with 7-MX appears to not only decrease the amount of myopia by around 50% and eliminate the eye elongation induced by form deprivation in guinea pigs, but also to prevent form deprivation myopia-related scleral changes, such as thinning of the sclera and thinning of the collagen fibril diameter in the posterior sclera.