Effect of chronic topical latanoprost on the sclera and lamina cribrosa of form-deprived myopic Guinea pigs.

Abstract

The purpose of this study was to investigate the effects of latanoprost, an ocular hypotensive prostaglandin analog, on scleral collagen fibers and laminar pores in myopic guinea pigs. Young guinea pigs underwent monocular form deprivation (FD; white plastic diffusers) from 14-days of age for 10-weeks. After the first week, FD eyes also received daily topical A) latanoprost (Lat, 0.005%, n\u202f=\u202f5) or B) artificial tears (AT; n\u202f=\u202f5). At the end of the treatment period, animals were sacrificed, eyes enucleated and optic nerve heads (ONH) excised to include a 4\u202fmm diameter ring of surrounding sclera for scanning electron microscopy (SEM), and an additional 6\u202fmm ring of sclera surrounding the ONH was excised for transmission electron microscopy (TEM). For SEM, ONH samples were first immersed in 0.2M NaOH for 30\u202fh to isolate the collagenous structures. All samples were stained with osmium tetroxide, dried through an ethanol series and finally subjected to critical point drying before imaging. Image J was used to analyze the dimensions of laminar pores (SEM images) and scleral collagen fibers (TEM images). As previously reported in a related study, latanoprost was effective in inhibiting myopia progression in FD eyes of the guinea pigs. The scleral fibers of FD myopic eyes treated with AT were smaller and more variable in cross-sectional areas compared to untreated (fellow) eyes (mean areas: 0.0059\u202f±\u202f0.0013 vs. 0.0085\u202f±\u202f0.002\u202fμm2; p\u202f<\u202f0.001), consistent with scleral changes reported for human myopia. In contrast, the scleral fibers of the Lat-treated FD eyes were similar to those of fellow eyes (0.0083\u202f±\u202f0.002 vs. 0.0078\u202f±\u202f0.0014\u202fμm2). However, laminar pore size appeared unaffected by either the FD or drug treatments, with no significant difference found between FD eyes and their fellows, for either treatment group. That daily topical latanoprost appeared to protect against myopia-related changes in scleral collagen, rather than exaggerating them, as might be predicted from its known action on the uveoscleral extracellular matrix, lends further support its use for myopia control. In this guinea pig myopia model, the lamina cribrosa appeared unaffected.