Abstract
Purpose :
To determine whether Fluence (F) is a better indicator than Total Energy (TE) in predicting IOP reduction with MicroPulse® Transscleral Laser Therapy (MP-TLT, Iridex Corp., Mountain View, CA) in patients with glaucoma.
Methods :
F and TE were calculated from data obtained from published literature. The F formula was adjusted to account for sweep velocity. F= (power (Watts) x duty cycle x dwell time (s)) / fiber area. Dwell time is exposure time divided by velocity of the sweep. TE= power x duty cycle x exposure time (s). Studies without a description of the treatment parameters (power, exposure time, number of sweeps per procedure) or less than 6 months follow-up were excluded. Boxplots were created to compare the distribution of F and TE, and its relationship with IOP reduction by separating the cohorts into Group A: “equal or lower than the median fluence”, and Group B: “above the median fluence”; and mixed effects models were used to compare the parameters between groups. All analyses were performed using R (version 4.0.0, R Foundation for Statistical Computing, Vienna, Austria).
Results :
Four of 30 (13.3%) publications included the number of sweeps used to allow for F calculation, yet personal communication with the authors allowed the inclusion of 6 more papers, which yielded a total of 656 eyes from 15 cohorts for analysis (some of the studies included more than one cohort).
Table 1 compares F, TE, baseline IOP, and IOP reduction between group A and group B. Figure 1 shows the distribution of these variables within the groups. Group B had a statistically higher IOP reduction than group A (p<.001), and there was no overlap in IOP reduction between the groups (Figure 1, top). TE was not statistically different between group A and group B (p=.447), and overlapped in the boxplot (Figure 1, bottom); suggesting that this variable may have less impact on IOP outcomes compared to F. Baseline IOP was not statistically different between the groups (p=.518).
Conclusions :
Most authors do not report the number of sweeps performed. This fails to account for the impact of sweep velocity on outcomes. In contrary to TE, F combines all the laser parameters including sweep velocity into a single number expressed in Joules/cm2. IOP reduction was statistically higher in the high F group (group B), suggesting that F may be a better light-dose metric and a more reliable indicator of IOP reduction than TE.
This is a 2021 ARVO Annual Meeting abstract.