Histologic changes in porcine eyes treated with high-intensity focused ultrasound.

High-intensity focused ultrasound (HIFU) has recently been described in the treatment of patients with glaucoma. However, despite previous studies in animal and mathematical models, the mechanisms of action are not completely understood. We therefore undertook a histologic study of 15 porcine eyes to evaluate the effect of HIFU and, in particular, the changes seen after sequential insonification on previously treated areas of sclera. We demonstrated initial scleral swelling that was followed by scleral thinning. The scleral thinning could be maximized by a second superimposed course of HIFU. The most consistent change in the ciliary body was necrosis of the pars plana. Some treated animals developed a hemorrhagic retinal detachment that we believe to be due to the presence of a circumferential blood vessel, which runs in the ora serrata of the pig but which is not present in humans. Based on our observations, possible mechanisms of action of this treatment are discussed.