Real-life outcomes of subthreshold laser therapy for diabetic macular edema

Renato M Passos,Marindia Rocha,Michel E Farah,Fernando K Malerbi,Maurício Maia

doi:10.1186/s40942-020-00268-3

Abstract

BackgroundDiabetic macular edema (DME) is a major cause of visual impairment and its treatment is a public health challenge. Even though anti-angiogenic drugs are the gold-standard treatment, they are not ideal and subthreshold laser (SL) remains a viable and promising therapy in selected cases. The aim of this study was to evaluate its efficacy in a real-life setting.Methods Retrospective case series of 56 eyes of 36 patients with center-involving DME treated with SL monotherapy. Treatment was performed in a single session with the EasyRet® photocoagulator with the following parameters: 5% duty cycle, 200-ms pulse duration, 160-µm spot size and 50% power of the barely visible threshold. A high-density pattern was then applied to the whole edematous area, using multispot mode. Best corrected visual acuity (BCVA) and optical coherence tomography (OCT) data were obtained at baseline and around 3 months after treatment.ResultsFifty-six eyes of 36 patients were included (39% women, mean age 64.8 years old); mean time between treatment day and follow-up visit was 14 ± 6 weeks. BCVA (Snellen converted to logMAR) was 0.59 ± 0.32 and 0.43 ± 0.25 at baseline and follow-up, respectively (p = 0.002). Thirty-two percent had prior panretinal photocoagulation (p = 0.011). Mean laser power was 555 ± 150 mW and number of spots was 1,109 ± 580. Intraretinal and subretinal fluid (SRF) was seen in 96 and 41% of eyes at baseline and improved in 35 and 74% of those after treatment, respectively. Quantitative analysis of central macular thickness (CMT) change was performed in a subset of 23 eyes, 43% of which exhibited > 10% CMT reduction post-treatment.ConclusionsSubthreshold laser therapy is known to have RPE function as its main target, modulating the activation of heat-shock proteins and normalizing cytokine expression. In the present study, the DME cases associated with SRF had the best anatomical response, while intraretinal edema responded poorly to laser monotherapy. BCVA and macular thickness exhibited a mild response, suggesting the need for combined treatment in most patients. Given the effect on SRF reabsorption, subthreshold laser therapy could be a viable treatment option in selected cases.

Highlights

Diabetic macular edema (DME) is a major cause of visual impairment and its treatment is a public health challenge
Recent understanding of the modification of gene expression mediated by the healing response of the Retinal pigment epithelium (RPE) to thermal injury [8] suggests that the useful therapeutic cellular cascade is activated not by laser-killed RPE cells, but by the still-viable RPE cells surrounding the burned areas that are reached by the heat diffusion at sublethal thermal elevation [9]
optical coherence tomography (OCT) quantitative and qualitative analyses Since we performed a retrospective analysis, we found out when collecting the data that some patients had their baseline and follow-up OCTs performed with different instruments (HRA Spectralis® by Heidelberg, Heidelberg, Germany; DRI-OCT Triton® by Topcon, Oakland NJ, USA or Avanti® by Optovue, Fremont CA, USA), which could make some comparisons unreliable such as central macular thickness (CMT)

Summary

Introduction

Diabetic macular edema (DME) is a major cause of visual impairment and its treatment is a public health challenge. Even though anti-angiogenic drugs are the gold-standard treatment, they are not ideal and subthreshold laser (SL) remains a viable and promising therapy in selected cases. The Early Treatment Diabetic Retinopathy Study (ETDRS) [7] had already demonstrated the beneficial effect of laser photocoagulation for treating clinically significant DME, reducing the chance of visual loss by 50% in 3 years despite its adverse effects such as retinal scarring, permanent scotomata, among others. In the years that followed, other authors evaluated different non-damaging macular laser modalities and strategies for DME treatment, with satisfactory results that were usually superior to that with conventional macular laser as proposed by ETDRS [9,10,11,12,13]. Besides the usual 810-nm wavelength already proven effective [9, 19, 20], yellow (577-nm) wavelength has shown good success and safety [21, 22], due to its intrinsic physiobiological characteristics, namely better penetration through media opacities, null absorbance by macular xanthophyll pigments and an excellent combined absorbance by melanin and oxyhemoglobin [23]

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