Barely Visible and Subvisible "Subthreshold" 577-nm Photothermal Therapy for Diabetic Macular Edema: Initial Clinical Experience

Abstract

 

Purpose

 

To investigate the morphologic features and clinical efficacy of Barely Visible and Subvisible "Subthreshold” 577-nm Photothermal Therapy in Diabetic Macular Edema (DME) and propose new treatment parameters.

 

Methods

 

Retrospective review. Ten eyes with newly diagnosed DME were treated with the 577-nm (yellow) wavelength PASCAL® Streamline® laser and assessed before and after treatment using Fourier-Domain (FD-OCT) and Swept-Source Optical Coherence Tomography (SS-OCT), Fundus Autofluorescence (FAF) and Fundus-related Perimetry (FrP). Proprietary Endpoint Management Software® (EpM®) was used to obtain uniform sub-threshold treatment spots within the treatment array. Laser power was first titrated for a Barely Visible 10ms 100μm retinal spot size which was defined as 100% pulse energy and which would become the “Landmark” spots to facilitate visualisation of treated areas. Treatment was applied over areas of retinal thickening as per FD-OCT maps, using either 40% or 70% pulse energy (Barely Visible or Subvisible "Subthreshold" spots) with an inter-spot spacing of 0.75 or 1 spot diameter. Best-corrected Visual Acuity (BCVA) and changes in Retinal Thickness (RT) were measured over a 6 months follow-up. Pre-treatment and post-treatment FAF and FrP Retinal Sensitivity were also assessed. The two-tailed Student’s t-test was used for statistical analysis.

 

Results

 

On average, 662 (309-1060) spots have been applied per eye to cover the areas of retinal thickening. No Subvisible "Subthreshold" laser spots could be detected on immediate post-treatment slitlamp examination. FD-OCT showed the Landmark but not the Barely Visible nor the Subvisible "Subthreshold" spots. However, they were visible on FAF and some of them progressively disappeared over time. There was a statistically significant reduction in RT (15%) on FD-OCT at 2 months compared with baseline in eyes treated with EpM® at 40% (p=0.02). BCVA and Retinal Sensitivity didn’t show any statistically significant improvement in either group.

 

Conclusions

 

This is the first report on the safety and clinical effectiveness of Barely Visible and Subvisible "Subthreshold” 577-nm PASCAL laser® with EpM® in DME. This technology may effectively reduce edema within treated areas with no enlargement nor coalescence of retinal treatment spots over 6 months. These new treatment parameters seem to be safe and effective.