Ultrasonic Circular Cyclocoagulation

Abstract

All treatments for glaucoma aim to reduce the intraocular pressure and can have two mechanisms of action: reducing aqueous humor production by the partial destruction or medical inhibition of the ciliary body and facilitating the evacuation of aqueous humor out of the eye. Several physical methods can be used to destroy the ciliary body, diode laser transscleral cyclophotocoagulation being currently the clinical standard. All the currently available methods have two major drawbacks which limit their use to the treatment of refractory and advanced glaucoma: they are nonselective of the organ to be treated, often resulting in damage to the adjacent structures and related side effects (ocular inflammation, cataract formation, etc.), and they have an unpredictable dose-effect relationship, which prevents accurate prediction of the treatment effect. Specific advantages of ultrasound, particularly when compared to laser, are that the energy can be focused through optically opaque media without uncontrolled energy absorption, especially through the sclera which is a strongly light-scattering medium, and that energy deposition and tissue heating at the focus site do not depend on tissue pigmentation, which may vary greatly, particularly in the ciliary body. Focused ultrasound is therefore a possible method for partial coagulation of the ciliary body. A commercially available device using ultrasound to coagulate the ciliary body (Sonocare Therapeutic Ultrasound System Model, Sonocare Inc., Ridgewood, NJ) was marketed in the 1980s and early 1990s. Despite being efficient to reduce IOP, the procedure was rather lengthy and complex to perform, and the use of ultrasound for cyclocoagulation was gradually abandoned in the mid-1990s. Taking advantage of recent breakthroughs in the field of high-intensity focused ultrasound (HIFU) technology, high-frequency miniaturized transducers were recently integrated into a small device with a circular design, adapted to the geometry of the ciliary body. This design allows this new device to be placed directly against the eye, thus enabling a one-step, quick, and reproducible treatment. Animal experiments have shown selective coagulation necrosis of the treated ciliary body. The first clinical trials performed in humans showed that this method is well tolerated and allows a significant, predictable, and sustained reduction in intraocular pressure, both in patients with refractory secondary glaucoma and in patients with primary open-angle glaucoma, whether naïve of previous filtering surgery or not.