The effect of Ultrasound cycloplasty (UCP) using High Intensity Focused Ultrasound (HiFU) on aqueous humor dynamics

Abstract

Purpose : Ultrasound cycloplasty (UCP) is a new procedure utilising High Intensity Focused Ultrasound (HIFU) for treating glaucoma. This study explores the effect of UCP on aqueous humor dynamics in patients with glaucoma.

Methods : All subjects attending the glaucoma clinic who had uncontrolled intraocular pressure (IOP) for treated primary open angle glaucoma (POAG) were offered UCP procedure. All UCP procedures were performed under peri-bulbar anaesthesia. Post-operatively, patients were treated topically with steroids for four weeks.
All glaucoma treatments were stopped, one month before the baseline and 3 months’ post-operative aqueous dynamic measurements.
Inclusion Criteria
All adult patients with uncontrolled POAG.
Exclusion Criteria
Previous intraocular surgery, except SLT/ALT laser
Other types of glaucoma
Use of systemic medication such as beta-blockers
A history of allergy to fluorescein
Outcome Measures
Intraocular pressure (Goldmann tonometry)
Facility of outflow (Schiøtz tonography)
Rate of aqueous flow (fluorophotometry)
Uveoscleral outflow (calculated from Goldmann’s equation)

Results : 32 patients were recruited into the study. One patient had very high IOP after 2 weeks’ washout and another patient had normal IOP after washout were withdrawn from the study.
Uveoscleral outflow was calculated using Goldmann’s equation with an assumed episcleral venous pressure of 10 mmHg.
F_{t =} C (IOP – P_v) + F_u
Therefore: F_u = F_t – C (IOP – P_v)
F_u= Uveoscleral outflow
F_{t =} rate of aqueous humor formation
C = tonographic facility of outflow
IOP = intraocular pressure
P_{v =} episcleral venous pressure

Table 1. Aqueous humor parameters comparison before and after HiFU treatment

Conclusions : This is the first study investigating aqueous humor dynamics after application of UCP in patients with uncontrolled POAG. We demonstrated that UCP reduced IOP 3-months postoperatively effectively by 14% whilst aqueous flow decreased by 11.3%. Moreover, tonographic outflow facility and calculated uveoscleral outflow remained unchanged.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.