Aim: To determine the effect of 7-methylxanthine (7-MX) on the posterior sclera of form-deprivation myopia (FDM) in pigmented rabbits.
Methods: Sixteen pigmented rabbits were monocularly deprived (MD) by suturing the right eyelids after natural eye opening (ten-day old) for a period of 30 days. Two groups of pigmented rabbits were fed either 7-MX (30 mg per kg body weight; n=8) or vehicle control (saline equal volume with 7-MX; n=8). Ocular refractions, axial lengths and body weights were measured at the start and the end of the experiment 30 days later. Electron microscopy was used to measure and determine the collagen fibril diameters in the posterior pole of sclera.
Results: In vehicle control MD pigmented rabbits, 30 days of MD produced -1.10D±0.78D of myopia and the axial length increased 0.51mm±0.09mm. In MD pigmented rabbits fed with 7-MX, 30 days of MD induced only -0.21D±0.11D of myopia and the axial length increased 0.07mm±0.10mm. There was significant change in axial length of vehicle control MD pigmented rabbits (13.11mm±0.19mm versus 12.60mm±0.06mm; P=0.03). The changes in refraction and axial length of two MD groups' contralateral eyes during the 30 days were not significantly different (2.75D±0.27D versus 2.75D±0.35D, P>0.05; 12.60mm±0.06mm versus 12.45mm±0.14mm, P>0.05). The weights of the two groups pigmented rabbits had no significant changes (187g±22.1g versus 189g±19.3g, P>0.05). The diameter of scleral collagen fibers increased in both eyes of 7-MX treated pigmented rabbits. There was significant difference in collagen fibril diameters of inner layer (111.34nm±28.30nm versus 94.80nm±27.52nm, P=0.002) and outer layer (167.92nm±55.82 nm versus 144.04 nm±47.02nm, P=0.016) in the posterior sclera between the myopic eyes of vehicle control MD group and contralateral eyes of 7-MX treated MD group.
Conclusion: 7-MX appears to prevent FDM in pigmented rabbits by remodeling the posterior sclera.
Keywords: 7-methylxanthine; myopia; pigmented rabbits.