Comparative Effectiveness and Tolerance of Subliminal Subthreshold Transscleral Cyclophotocoagulation With a Duty Factor of 25 % Versus 31.3 % for Advanced Glaucoma

Glaucoma, progressive optical neuropathy, is the leading cause of irreversible blindness in the world. Glaucoma treatment aims to lower intraocular pressure (IOP) by using medication, laser and surgery. Patients suffering from refractory and advanced glaucoma with impaired visual field who are not good candidates for surgery, cadenced subcleral transscleral cyclophotocoagulation (CPCTSI) is commonly used to reduce IOP. The CPCTSI consists in delivering short bursts of energy (in cycle) to the ciliary body, thus reducing production of aqueous humor. The energy gusts develop sequentially to a photocoagulating state in the pigmented epithelium. They are spaced by rest periods that allow surrounding tissue to cool down and remain below photocoagulative threshold, thus avoiding damage to surrounding tissue. Some studies have shown that the risk of complications increases with higher energies. Complications associated with CPCTSI include prolonged intraocular inflammation, pain, intraocular hemorrhage, hypotonia, phthysis, decreased vision and sympathetic ophthalmia. Severity of these complications depends on collateral damage inflicted on surrounding tissues: ciliary muscles, unpigmented epithelium and stroma of ciliary body. Currently, CPCTSI with a cycle ratio of 25% and 31.3% are used in surgical routine in ophthalmology. Cycle ratio is ratio between duration of gusts and total duration of cycle (gusts and rest periods). At St. Joseph's Hospital, both cycle ratios are used and the choice is operator dependent. However, using CPCTSI with a 25% cycle ratio could have fewer complications while maintaining similar efficacy. To our knowledge, there are no studies comparing these two cycle reports, although they are commonly used in practice. Our objective is to compare the CPCTSI with a cycle ratio of 25% and 31.3%.