Ultrasound Cycloplasty in Glaucoma – Mechanisms of Action and their Possible Impact on Intraocular Pressure

U ltrasound cycloplasty (UCP) is a procedure based on high-intensity focused ultrasound (HIFU) for refractory and non-refractory glaucoma in cases for which surgery is not suitable. UCP may bring about a reduction in intraocular pressure (IOP) via multiple mechanisms of action that result in a decrease in aqueous humour production and increase in aqueous humour evacuation. UCP appears to have a favourable safety profile compared with cyclo-destructive methods, with no phthisis bulbi, no induced cataract, and no persistent hypotony. In 103 patients with refractory and non-refractory glaucoma who underwent UCP, 94 (91%) achieved an initial reduction in IOP, and in 65 patients (63.1%), treatment success was achieved whereby the IOP remained low. However, in 22 patients (21.4%), at 3 months, the IOP rose to near the original level, indicating treatment failure: ‘early failure’. In the remaining 7 patients (6.8%), a slow rise in IOP occurred over 6 months following the procedure: ‘late failure’. The differences in IOP changes in these 94 patients may be in part explained by: (i) a reduction in the uveoscleral–transscleral openings in some patients, leading to an eventual rise in the initially decreased IOP; (ii) a possible re-epithelialisation of the ciliary processes taking place in some cases; and/or (iii) that the circumference of 160° UCP treatment might not be sufficient for all patients. The first 3 months following the UCP procedure are therefore critical since treatment success or failure is determined within this timeframe.