Comparison Between Two Techniques of Subthreshold Diode Laser Cyclophotocoagulation in Refractory Glaucoma

Refractory glaucoma is glaucoma that doesn't respond favorably to surgical and/or medical treatment to lower intraocular pressure. It can include primary open angle glaucoma, primary angle closure glaucoma, neovascular glaucoma or silicone oil-induced glaucoma. Cyclophotocoagulation (CPC) is a form of cycloablation using laser to treat glaucoma. It involves ciliary body destruction by targeting the ciliary epithelium and stroma, resulting in a reduction in aqueous secretion and hence intraocular pressure. Transscleral cyclophotocoagulation using a continuous diode laser has been a treatment option in advanced glaucoma cases with s¬¬uboptimal IOP control, for a long time. High treatment energy used by diode laser cyclophotocoagulation was argued to be associated with increased frequency of serious complications such as vision loss, hypotony, and phthisis. These concerns necessitate modulation of the parameters of laser treatment used.

Micropulse transscleral cyclophotocoagulation (MP-TSCPC), which is a variation of conventional continuous-wave CPC, has emerged as an attractive alternative for the treatment of many types of glaucoma. It breaks the continuous wave laser into multiple short and repetitive pulses that allow the tissue to cool down between applications, thus reducing thermal damage. This strategy delivers very short energy pulses followed by rest periods, which is known as "duty cycle" and is defined as the ratio of time that a laser is delivering energy vs resting (ON/OFF). For this procedure, an infrared diode laser is used to stimulate the ciliary body structures and the uveoscleral pathway. This way it reduces the production of the aqueous humour and facilitates the uveoscleral outflow, with IOP reduction as a final effect.

Despite promising results, only few clinical studies are published on MP-TSCPC and most of them are retrospective studies refer to patients having previous continuous wave transscleral cyclophotocoagulation. Moreover, Several parameters and protocols have been studied in other reports in an attempt to refine the standard technique aiming to improve the outcomes without increasing the adverse effects.