Comparison of Iridex MP3 and P3 probes on long-term intraocular pressure control after MicroPulse Transscleral-Cyclophotocoagulation

Purpose: Micropulse transscleral cyclophotocoagulation (MP-TSCPC) is a glaucoma procedure that delivers energy to the ciliary body with minimal collateral-damage. We aim to assess the long-term effectiveness of MP-TSCPC using the original MP3 and revised P3 probe. Methods and design: Baseline Retrospective cohort study was performed to obtain baseline characteristics, intraocular pressure (IOP), number of IOP-lowering medications, and best-corrected visual acuity (BCVA) were obtained from pre- and post-operative visits of patients treated with MP-TSCPC. Failure was defined as IOP>21 mmHg, reduced IOP<20% below baseline, or IOP<5 mmHg on 2 consecutive follow-up visits after post-operative month 1, reoperation for glaucoma, or loss of vision to no light perception. Results: A total of 113 eyes were enrolled, 44 using the MP3 probe and 69 with the revised P3 probe. Survival analysis found a 75% failure rate in patients treated with the revised P3 probe by the final visit with a mean time to failure (MTTF) of 4.8 ± 0.7 months which was higher than the original probe at 66% failure rate with a MTTF of 6.1 ± 1.1 months (p = 0.04). All causes of failure were due to high IOP and 67% required repeat treatment with MP-TSCPC or incisional surgery. Prior to censure of data from failure, both probes had significant reduction in IOP compared to pre-operative IOP at all time points. No significant changes in BCVA were found. Both groups were associated with low rates of complications. Conclusion: Both probes had a very low rate of visually significant complications when performed in a standardized method in accordance with surgical procedure and power settings recommended by Iridex; however, were associated with a high rate of single procedure failure due to uncontrolled IOP over the long term. The revised P3 probe was associated with a higher rate of failure. Patients experienced a reduction in IOP; however, a large proportion required additional treatment compared to the original MP3 probe.