Regional Changes of Iris Stiffness in the Rabbits Suffered from Chronic High Intraocular Pressure

To explore the effects of chronic high intraocular pressure (IOP) on the iris stiffness in different regions (iris root, mid-periphery and pupillary-margin). We established rabbit animal models with chronic high IOP by injecting α-chymotrypsin into the posterior chamber of the left eyes of rabbits, while their right eyes were regarded as self-blank control eyes. After a 26-week duration of chronic high IOP, rabbits were sacrificed and irises were removed from the eyes globe. The iris stiffness in different regions was measured by atomic force microscope. The iris in treated eye was significantly stiffer than that in control eye in iris root (1.9 times), mid-periphery (2.0 times) and pupillary-margin (2.3 times), p < 0.05. In treated eye, the iris in pupillary-margin was significantly stiffer than that in iris root and mid-periphery, p < 0.05. In control eye, the iris in pupillary-margin was significantly stiffer than that in mid-periphery, p < 0.05. Histological analysis showed that in treated eye, the iris thinned and the number of iris pigment cells in the stroma decreased. Under chronic high IOP, rabbit iris stiffness increases. The difference in mean iris stiffness between pupillary-margin and mid-periphery in the treated eye is higher than that in the control eye. It needs to investigate whether the regional difference of iris stiffness affects the flow field of aqueous humor in the anterior segment and leads to further elevation of IOP.