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

Abstract

 

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 SD-OCT, and to evaluate its efficacy in obliterating retinal diabetic microaneurysms.

 

Methods

 

A retrospective study of eyes that were diagnosed with non-foveal involving DME and underwent subthreshold laser treatment with the Lumenis Novus SRT system. SD-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-retinal pigment epithelium (RPE) layer, the retinal thickness at the treatment sites, and the diameter of the microaneurysms.

 

Results

 

Nineteen eyes and 31 microaneurysms were included in this study. Following treatment, the continuity of the inner / outer segments junction of the PR was confirmed in all but two cases. The thickness of the PR-RPE layers was 72.32 ± 7.36 µm 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 µm to 372.74 ± 60.4 µm (p<0.001). The mean axial diameter of the microaneurysms was 87.32 ± 27.45 µm and 6.68 ± 26.12 µm, respectively (p<0.001).

 

Conclusions

 

In this study, subthreshold laser treatment of retinal diabetic microaneurysms has been shown to be efficacious and safe, as demonstrated by SD-OCT.

 

 

A A color fundus photograph of the right eye of one of the study's participants. B Fluorescein angiography (FA) performed two hours following subthreshold laser treatment in the same eye. The studied microaneurysms are circled in this early phase image. C A late phase image from the same FA study. The studied microaneurysms are circled. D Pre-treatment: an infrared scan on the left side of the panel, and an SD-OCT scan on the right. The studied microaneurysms are circled. The PR-RPE layers are depicted within the red rectangle. The asterisked rectangle is a magnification. E Four months post treatment: the vertical lines mark the former locations of the microaneurysms, which are now undetectable. The PR-RPE layers are within the blue rectangle, and the asterisk marks a magnified view.

 

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 688 retina • 499 diabetic retinopathy