Preservation of the Photoreceptor Layer Following Subthreshold Laser Treatment for Diabetic Macular Edema As Demonstrated by SD-OCT

Purpose: Subthreshold laser treatment of diabetic macular edema (DME) may have less deleterious effects on the photoreceptors than regular continuous wave laser. This study aimed to assess whether subthreshold laser causes a long-term damage to the retinal structures, as demonstrated by spectral-domain optical coherence tomography (SD-OCT), and to evaluate the change in the axial diameter of retinal diabetic microaneurysms following treatment.

Methods: A retrospective study of eyes that were diagnosed with nonfoveal involving DME and underwent subthreshold laser treatment with the Novus SRT system. Spectral-domain OCT scans of treated retinal areas, performed prior to treatment and approximately 4 months following treatment, were assessed for changes in the continuity of the photoreceptor (PR) layer, the thickness of the PR-RPE layer, the retinal thickness at the treatment sites, and the diameter of the microaneurysms.

Results: Included in this study were 31 microaneurysms. Following treatment, the continuity of the ellipsoid zone of the inner segments of the photoreceptors was confirmed in all but two cases. The thickness of the PR-RPE layers was 72.32 ± 7.36 and 70.97 ± 7.27 μm prior to and following treatment, respectively (P = 0.061). The retinal thickness at the treatment sites decreased from 398.65 ± 57.89 to 372.74 ± 60.4 μm (P < 0.001). The mean measured diameter of the microaneurysms was 87.32 ± 27.45 and 6.68 ± 26.12 μm, respectively (P < 0.001).

Conclusions: In this study, subthreshold laser treatment for DME has been shown to be a safe technology that preserves the photoreceptor layer, as demonstrated by SD-OCT.