In this study, the investigators demonstrated that in vivo THG microscopy can differentiate Solar lentigos (SL), Nevus zygomaticus(NZ) and normal skin based on the optical nature of melanin. This THG-based procedure provides a valuable tool for noninvasive determination of third-order nonlinear susceptibility of melanin within the skin. It can also provide real-time histopathology information for treatment follow-up, without performing an invasive skin biopsy.

A nonrandomized, controlled, split-face comparative study was conducted to compare the efficacy and safety between quality-switched ruby laser (QSRL) and 532-nm picosecond Nd:YAG laser (532-PSNYL for SL, 1064-PSNYL for NZ) in the treatment of solar lentigo clinically and histologically by harmonic generation microscopy (HGM). After baseline photography and in vivo harmonic generation microscopy (HGM) imaging, QSRL and 532-PSNYL or 1064-PSNYL therapy for solar lentigos and nevus zygomaticus on the left and right side of the face, respectively, were performed for each subject. The subjects underwent follow-up assessment at weeks 3 and 6.

Statistical analysis: All data gathered went through decoding and were analyzed by blinded evaluators using SPSS software (version 20.0; IBM, Armonk, NY). All tests were two-sided. A P value of < .05 was considered to be statistically significant.

1. Main inclusion criteria:

1. Subjects are aged 20 to 85 years at Screening, and can be either sex.
2. Subjects are Fitzpatrick skin type III or IV.
3. Subjects must have been diagnosed to have solar lentigos or nevus zygomaticus, which are larger than 4 mm in diameter on both sides of the face.

2. Main exclusion criteria:

1. Subjects have previous treatments on the solar lentigos or nevus zygomaticus.
2. Subjects have a history of adverse reaction to laser treatments, including allergy to topical anesthesia application.
3. Subjects have a history of chronic inflammatory disorder such as atopic dermatitis on the face.
4. Subjects are pregnant or breast feeding.
5. Subjects have frequent sun exposure (≥4 hours per day).