Focal Laser for Macular Edema: Recent Advances

Background and Historical Context

• Clinically significant macular edema (CSME) not involving the foveal center
• Diabetic ME refractory or partially responsive to anti-VEGF
• Branch retinal vein occlusion (BRVO)-related ME when anti-VEGF is unavailable or as adjunct
• Microaneurysm-targeted (focal) treatment for chronic, refractory DME

1. Conventional Focal/Grid Laser — Evolving Role

• Microaneurysm closure reduces local VEGF leakage and fluid accumulation
• Particularly effective for chronic, refractory edema where anti-VEGF response is incomplete or waning
• An emerging strategy uses anti-VEGF first for rapid visual recovery, then adds focal laser for durability — reducing injection burden over the long term (Nozaki et al., 2023, PMID: 37512130)

2. Subthreshold Micropulse Laser (SML) — Major Advance

Mechanism

• Delivers laser energy in repetitive short bursts (microseconds ON) separated by cooling intervals (OFF period) — the duty cycle (typically 5–15%)
• Maintains RPE temperature just below the damage threshold → no visible burn, no scotoma, no retinal scarring
• Triggers RPE cellular responses: heat shock protein (HSP) activation, cytokine modulation, reduction of pro-inflammatory factors, and restoration of the outer blood-retinal barrier ("reset theory" of RPE restoration)
• Wavelengths used: 577 nm (yellow, most common), 810 nm (infrared), 532 nm (green)

Clinical Evidence

• Comparable anatomical and visual outcomes to conventional laser for DME, with markedly better safety profile
• Reduces anti-VEGF injection burden when used adjunctively — a clinically important benefit for treatment fatigue
• Effective for: DME, central serous chorioretinopathy (CSCR), ME from RVO, and emerging data in AMD and pseudophakic ME
• A 2024 review (Mei & Lin, PMID: 38315299) confirmed slow onset but durable effect; HbA1c and baseline central macular thickness (CMT) predict outcomes
• Sabal et al. (2022, PMID: 36615074) proposed a practical protocol: 577 nm, 200 µm spot, 200 ms pulse, 400 mW, 5% duty cycle over entire macula, effective for mild-to-moderate edema (CMT < 400 µm)
• A 2026 narrative review (Sim et al., Survey of Ophthalmology, PMID: 41763458) confirmed SML's role across multiple retinal diseases but noted persistent lack of standardized protocols as the main limitation

Key Limitation

3. Pattern Scan Laser (PASCAL)

• Semi-automated system delivering multiple pre-programmed laser burns in a single footswitch press
• Short pulse durations (10–20 ms vs. 100 ms for conventional) → minimal thermal spread, reduced collateral damage
• The "sandwich technique" (Cardillo et al., 2022, PMID: 35655248) combines PASCAL short-pulse burns (juxta/perifoveal, OCT-guided) with subthreshold endpoint-management (EpM) burns over the broader macular area — in a 37-patient series, CST fell from 457 µm to 272 µm (p < 0.001) and BCVA improved significantly over 19 months

4. Navigated Laser Systems (Navilas)

• Integrates real-time multimodal imaging (FA, OCT, fundus photography) directly into the laser delivery system
• Operator pre-plans treatment targets (microaneurysms, leakage sites) on imaging overlays; system automatically navigates to each target, compensating for eye movements
• Enables precise microaneurysm-targeted photocoagulation with minimal collateral burns
• Ikegami et al. (2023, PMID: 36864536) showed navigated short-pulse (30 ms) direct photocoagulation reduced edema area thickness without decreasing retinal sensitivity at coagulated spots — confirming functional safety
• A 2026 study (Oliverio et al., PMID: 41875416) combined dexamethasone implant with navigated subthreshold micropulse yellow laser for DME, showing additive benefit

5. Selective Retina Therapy (SRT) and Nanosecond Lasers

• SRT: Uses microsecond-pulsed laser to selectively destroy RPE cells while sparing photoreceptors; RPE regeneration then restores barrier function
• Nanosecond lasers: Ultrashort pulse durations (<1 µs) create microbubbles selectively around RPE melanosomes — extremely precise, minimal thermal damage
• Both are reviewed as emerging minimally traumatic technologies (Yao & Paulus, 2025, PMID: 41196067); early results are promising but larger trials are pending

6. Multimodal Imaging-Guided Laser

• Integration of OCT angiography (OCTA), fluorescein angiography, and structural OCT to precisely map leaking microaneurysms and guide treatment
• Allows selection of truly active leakage sources vs. non-leaking MA — improves hit rate and reduces unnecessary burns
• Considered essential for achieving "minimally invasive coagulation" in current practice (Nozaki et al., 2023)

7. Combination Strategies (Laser + Pharmacotherapy)

Summary of Laser Technologies by Profile

Key Takeaways

1. Anti-VEGF remains the primary treatment for center-involving DME and RVO-ME; focal laser is now adjunctive or second-line in most cases.
2. Subthreshold micropulse laser is the most important advance — it reduces injection burden without visible scarring and is now widely used adjunctively.
3. Navigated and imaging-guided systems have made microaneurysm-targeted treatment more precise and functionally safe.
4. Combination laser + pharmacotherapy is an active research area, with evidence that laser can extend anti-VEGF durability.
5. The main unresolved challenge remains lack of standardized SML parameters across wavelengths, duty cycles, and fluence levels.

Key Recent References

• Subthreshold Micropulse Laser — narrative review 2026 (Survey of Ophthalmology, PMID 41763458)
• Advances in minimally traumatic retinal laser, 2025 (Expert Rev Med Devices, PMID 41196067)
• Laser for DR: history and novel technologies, 2024 (J Clin Med, PMID 39336925)
• Role of laser in DME in the anti-VEGF era, 2023 (Medicina, PMID 37512130)
• SML for DME: biological impact and safety, 2024 (Int Ophthalmol, PMID 38315299)