High-intensity focused ultrasound for glaucoma

2.1 Glaucoma is usually a chronic condition associated with elevated intraocular pressure. The most common type of glaucoma in the UK is primary open-angle glaucoma, also known as chronic open-angle glaucoma. It leads to progressive damage to the optic nerve. Early stages are usually asymptomatic but as the condition progresses it causes visual impairment and, if untreated, blindness.

2.2 NICE's guideline on glaucoma describes its diagnosis and management. Treatment is usually eye drops containing drugs that either reduce the production of aqueous humor (fluid) or increase its drainage. Surgical procedures such as trabeculectomy, drainage tubes, deep sclerectomy, viscocanalostomy or laser trabeculoplasty may also be used.

2.3 This procedure uses high-intensity focused ultrasound (HIFU) to partially destroy the ciliary body to reduce the production of aqueous humor and thereby decrease the intraocular pressure.

2.4 The procedure can be done under regional, general or topical anaesthesia. One device available for this procedure consists of a compact operator console and a disposable probe (which includes a coupling cone and a therapy probe that generates the ultrasound beams). The coupling cone is placed directly on the centre of the patient's cornea and held in place by a low-vacuum suction ring. A ring-shaped therapy probe (connected to the console) that generates ultrasound beams is inserted into the cone. The space between the eye, cone and the probe is filled with saline solution to ensure dissemination of ultrasound energy. By pressing the foot switch, miniature transducers in the ring-shaped probe are sequentially activated to deliver HIFU beams directly into the ciliary body. These beams pass through the scleral tissue without disruption of ocular tissue to reach the ciliary body. The ultrasound heats and inactivates tissue within the ciliary body to decrease the production of aqueous humor.