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/cm 2 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/cm 2 ), while higher fluences (0.05–0.2 J/cm 2 ) 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.
Peng et al. (Wed,) studied this question.