Influence of Total Energy Delivery on Success Rate after Contact Diode Laser Transscleral Cyclophotocoagulation: A Retrospective Case Review and Meta-analysis

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Abstract
To evaluate the effect of a single treatment of contact diode laser transscleral cyclophotocoagulation (TSCP) on intraocular pressure (IOP) in patients with refractory glaucoma and perform a historical meta-analysis of the relationship between successful IOP control and various laser parameters. Clinical data for 47 eyes of 43 patients who underwent a single session of contact diode laser TSCP (power of 2000 mW, exposure time of 2 seconds and 25.6 average applications) for refractory glaucoma at Pasco Eye Institute between 1996 and 2001 were reviewed. Baseline IOP was compared with the postoperative IOP at 1 month, 3 to 6 months, and 1 year. Snellen visual acuity and the number of glaucoma medications being used 3 to 6 months postoperatively were compared with baseline. Complications were also evaluated. The relationship between successful IOP control and various laser parameters (energy applied per eye, energy per laser application, power, exposure time and number of laser applications) was examined using the results of this study and previous investigations. The mean ± standard deviation (SD) baseline IOP was 29.4 ± 10.9 mm Hg. Diode laser TSCP decreased average IOP to 15.7 ± 12.0 mm Hg at 1 month, 16.3 ± 4.2 mm Hg at 3 to 6 months, and 16.2 ± 4.8 mm Hg at 1 year, postoperatively. This represents an IOP reduction of ∼45%. The percentage of patients maintaining a postoperative IOP of <21 mm Hg was 95.7% at 1 month, 92.1% at 3 to 6 months, and 94.4% at 1 year after TSCP. At the 3 to 6 month postoperative visit, the average ± SD change in Snellen visual acuity (−0.5 ± 1.1 lines) and the number of glaucoma medications used did not differ significantly from baseline. Combined analysis of the results of this study and previous studies reveals a linear, direct correlation (r = 0.91) between the percentage of patients achieving a successful outcome (defined as a final IOP < 21 or 22 mm Hg) and the total energy delivered to the ciliary body during the treatment session. Diode laser TSCP is a safe and highly effective method for lowering IOP in patients with uncontrolled glaucoma. Higher total energy levels in a given treatment session appear to be associated with increased success as defined by the percentage of patients achieving an IOP < 21 or 22 mm Hg, without an increased risk of additional complications or vision loss.