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. 2021 Jan 9;7(1):4.
doi: 10.1186/s40942-020-00268-3.

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

Renato M Passos  1   2 , Fernando K Malerbi  1   2 , Marindia Rocha  3 , Maurício Maia  1 , Michel E Farah  1
Affiliations

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

Renato M Passos et al. Int J Retina Vitreous. .

Abstract

Background: 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 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.

Results: Fifty-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.

Conclusions: Subthreshold 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.

Keywords: Diabetic macular edema; Diabetic retinopathy; Non-damaging retinal laser; Retinal photocoagulation; Subthreshold micropulse laser.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
a Baseline OCT depicting intraretinal fluid (*) and subretinal fluid (•), plus a focal disruption of ellipsoid zone (arrow) in the subfoveal area. b 3 months after SL treatment showing resolution of SRF but no visible effect on IRF (VA remained 20/60)
Fig. 2
Fig. 2
Histogram depicting baseline (x axis) and follow up (y axis) central macular thickness values (µm) for 23 eyes evaluated in the same OCT device. All dots below the reference line represent eyes that had CMT reduction at follow up with laser monotherapy
See this image and copyright information in PMC

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