Ultra-low fluence 532 nm picosecond laser treatment for acne scars: OCT-observed epidermal vacuole-like changes–a case report

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: was applied (8-mm spot size, 4 passes, 2,511 total pulses). Results: ) 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.