Effect of induced myopia on scleral myofibroblasts and in vivo ocular biomechanical compliance in the guinea pig.

PURPOSE To examine the effect of induced myopia on scleral myofibroblast populations and in vivo ocular biomechanical compliance. METHODS One-week-old guinea pigs were monocularly deprived (MD) of form vision for 2 weeks. Ocular biomechanical compliance was measured in both eyes of anesthetized animals by increasing the intraocular pressure (IOP) to 50 mm Hg for 1 hour, while A-scan ultrasound measures were made every 10 minutes to investigate the change in axial length. The total cell population and myofibroblast subpopulation of the posterior 100° of the sclera was determined with immunohistochemical techniques. RESULTS The vitreous chamber depth (VCD) of MD and contralateral control eyes showed significant elastic expansion on increasing the IOP, compared with that of the nonmanipulated normal eyes. The creep response of the VCD in response to increased IOP was initially greater in the normal eyes until eye length was similar to the MD and control eyes. An unexpectedly high proportion of the scleral cell population were myofibroblasts (63.7% ± 1.7%, average ± SEM; n = 30). MD significantly decreased the total number of cells in the region between the optic nerve and 10° nasal (equivalent to myopic crescent location in humans) compared with the number in control or normal eyes, but no significant effect on myofibroblasts or the total number of cells was found elsewhere. CONCLUSIONS A high proportion of scleral cells have contractile potential. This proportion is unaffected by MD. However, there is a significant difference in the in vivo elastic response of the sclera between MD and normal eyes, suggesting that factors other than number of cells have an effect on axial length.