UBM evaluation of mechanisms that drive intraocular pressure (IOP) decrease after ultrasound ciliary plasty (UCP) with high intensity focused ultrasound (HIFU), towards a new explanation of the role of uveoscleral pathway outflow

Purpose Ultrasound ciliary plasty technique is a new therapeutic approach in refractory glaucoma under maximal hypotensive medication, with coagulation of ciliary body. Our UBM evaluation found an atrophy of the ciliary body (ACB) as well as an widening of the uveo-scleral pathway (UP). We evaluated the correlation between UBM observations and IOP decrease. Methods We conducted a prospective, observational, monocentric study, with 24 eyes from 19 patients, recruited between July 2015 and October 2016, undergoing systematic pre-operative and postoperative visits at D7, M1, M3 with IOP measurement and UBM in 8 axes (the 6 ultrasound-treated zones and 2 non-treated zones).The evaluation of the UBM pictures was conducted by 2 experienced surgeons, analyzing the existence or absence of a de novo UP as well as the ACB. Results ACB was found to be significant in UBM pictures and predominant in the therapeutic success group (60% of the axes analyzed for at least one of the reviewers for patients with IOP decrease maintained at M3 follow-up versus 46% of axis in case of failure (p = 0.17).An opening of the UP was observed in the UBM pictures, observable in 53% of axes with patients in success group versus 45% of axis in patients whose IOP had failed to decrease. UBM found a gradual narrowing of the possible UP during the follow-up in more than half of the axes analyzed irrespective of the IOP result. Conclusions The mechanisms of action responsible for IOP decrease after UCP have not been studied in great enough detail so far. Our study highlights several mechanisms contributing to IOP decrease: on the one hand, the decrease of the aqueous humor production by means of atrophy of the ciliary processes; and on the other, a second - and less expected phenomenon - of an increase in aqueous humour outflow due to a wider uveoscleral pathway, clearly visible in UBM pictures.