Gradient Myopic Defocus Causes Chick Scleral Tissue Reinforcement and Structural Scleral Remodeling

To determine histological effects of myopia progression control (MPC) lens-induced refractive changes on scleral remodeling in chicks. 24 Ross-Ross chicks were raised for 14 days. 6 chicks wore conventional -10D lenses for 7 days, followed by no lenses for 7 days. 6 chicks wore conventional -10D lenses for the full 14 days. 6 chicks wore conventional -10D lenses for 7 days, followed by +10D lenses for 7 days. 6 chicks wore conventional -10D lenses for 7 days, followed by MPC lenses for 7 days. MPC lenses had a central power of -10D and a gradient power rise at pupil edge (+2.75D). Chicks were euthanized after 14 days and eyes were processed for histopathological evaluation. Whole mount H&E-stained tissue sections were analyzed using bright field microscopy. Total scleral thickness was significantly reduced in the group wearing conventional -10D lenses (p < 0.05) but remained comparable to the control group for MPC lenses treated chicks. Appositional growth of the cartilaginous sclera (CS) was observed in all MPC lenses treated eyes and only in those eyes. There was a significant increase in CS thickness in MPC lenses treated chicks compared to the other two groups (p < 0.03) but not between conventional -10D lens treated and control chicks (p > 0.05). It is possible to induce appositional growth in hyaline cartilage in the chick sclera. In our study, this has only been achieved by using MPC lenses to reverse previously induced experimental myopia with conventional minus lenses. Our findings suggest that a gradient decrease in peripheral lens power and the resulting differential defocus could trigger of scleral reinforcement through of cartilage growth stimulation in the chick sclera.