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Ultra-low fluence 532 nm picosecond laser treatment for acne scars: OCT-observed epidermal vacuole-like changes-a
Patricia Yu-Chun Peng1, Hung-Chia Chang2, Hsien-Li Peter Peng2,3
1Kaohsiung Medical University Hospital, Kaohsiung, Taiwan.
Background:
Treating atrophic acne scars in Asian skin (Fitzpatrick types III-V) is challenging due to the elevated risk of post-inflammatory hyperpigmentation (PIH). While picosecond lasers with fractional handpiece treatment are effective, the optimal balance between fluence, passes, clinical outcome, and downtime remains controversial.
Case Presentation:
A 28-years-old Asian male with moderate atrophic acne scars was treated with a 532-nm picosecond Nd:YAG laser using a fractional handpiece. An ultra-low fluence of 0.03 J/cm2 was applied (8-mm spot size, 4 passes, 2,511 total pulses).
Results:
Clinical follow-up demonstrated observable changes in scar contour and skin surface irregularity after a single treatment session, without downtime or PIH. Optical Coherence Tomography (OCT) revealed intraepidermal vacuole-like structures exclusively at the ultra-low setting (0.03 J/cm2), while higher fluences (0.05-0.2 J/cm2) failed to generate similar discrete OCT findings.
Conclusion:
Ultra-low fluence, high-pulse-count 532-nm treatment may be associated with OCT-detectable intraepidermal vacuole-like response not observed at higher fluences. While the biological mechanism remains to be elucidated, these findings highlight the possibility of a non-linear dose-response phenomenon and support further investigation into sub-threshold treatment paradigms in pigment-prone populations.
