Highlights
- Diabetic macular edema (DME) is a major cause of vision loss in diabetes and is driven by retinal fluid leakage.
- Shen et al. (2020) explored whether photobiomodulation (PBM) — low-intensity red light (670 nm) — could help reduce retinal swelling.
- The results were encouraging: central macular thickness decreased, especially at higher doses, and effects were seen out to 6 months.
- Visual acuity changed only modestly, which may relate to good baseline vision in many participants.
- Treatment was reported as well tolerated, with no significant side effects, even at the highest tested dose.
Why DME is challenging
DME occurs when tiny retinal blood vessels become leaky, allowing fluid to accumulate in the macula — the part of the retina responsible for sharp central vision. Standard options like anti-VEGF injections and steroid implants can help control leakage, but they often require frequent visits and ongoing procedures, which can be burdensome for patients.
This is why researchers are exploring additional approaches that are non-invasive and potentially easier to deliver over time.
What is photobiomodulation (PBM)?
PBM uses low-intensity light to influence cellular function — often described as supporting mitochondrial activity and reducing oxidative stress. In this work, the team used 670 nm red light, selected for its relevance to retinal cellular metabolism.
What the researchers tested
This project included both lab experiments and an early-stage clinical trial.
1) Laboratory and translational testing (safety + biological signal)
- In models of retinal injury, PBM delivered via LED was associated with:
- increased mitochondrial activity in photoreceptors
- reduced cell damage
- reduced abnormal vascular leakage
- Before treating people, the team developed a purpose-built retinal PBM laser and tested it in:
- cultured retinal cells (Müller cells)
- rat eyes
These steps supported feasibility and safety at appropriate settings.
The clinical trial (Phase IIa, open-label)
- Location: Sydney Eye Hospital
- Participants: 21 patients with center-involving DME
- Protocol:
- 12 sessions over 5 weeks
- 670 nm retinal PBM laser
- 90 seconds per treatment zone
- Delivered through a standard fundus lens
- Dose groups:
- 25 mW/cm²
- 100 mW/cm²
- 200 mW/cm²
- Safety step: the central fovea was protected by masking a 1 mm central zone during treatment.
What changed in the eye (main outcome)
Retinal swelling (Central Macular Thickness, CMT)
- 2 months: the highest-dose group (200 mW/cm²) showed a significant average CMT reduction of 59 ± 46 μm (p = 0.03).
- 6 months: significant reductions were reported across all dose groups:
- 53 ± 24 μm (25 mW/cm²; p = 0.04)
- 129 ± 51 μm (100 mW/cm²; p < 0.01)
- 114 ± 60 μm (200 mW/cm²; p < 0.01)
Vision (Best-Corrected Visual Acuity)
- Vision improved slightly at 2 months but did not show significant gains at 6 months.
- The authors noted that baseline vision was already relatively good for many participants, which can make improvements harder to detect.
Safety and tolerability
The treatment was reported as well tolerated, with no significant side effects, including at the highest tested dose.
Takeaway
Shen et al. (2020) provide early evidence that retinal PBM with 670 nm red light may help reduce retinal swelling in DME, with dose-related anatomical improvements observed over several months. While this was a small, open-label study (not randomized), the results support larger controlled trials to determine:
- who benefits most
- optimal dosing and scheduling
- whether PBM could complement existing care and potentially reduce treatment burden over time
Reference: Shen, W., Teo, K.Y.C., Wood, J.P.M. et al. Preclinical and clinical studies of photobiomodulation therapy for macular oedema. Diabetologia 63, 1900–1915 (2020). https://doi.org/10.1007/s00125-020-05189-2