Wavelength-dependent threshold fluences for melanosome disruption to evaluate the treatment of pigmented lesions with 532-, 730-, 755-, 785-, and 1064-nm picosecond lasers

BACKGROUND AND OBJECTIVES

A threshold fluence for melanosome disruption has the potential to provide a robust numerical indicator for establishing clinical endpoints for pigmented lesion treatment using a picosecond laser. Although the thresholds for a 755-nm picosecond laser were previously reported, the wavelength dependence has not been investigated. In this study, wavelength-dependent threshold fluences for melanosome disruption were determined. Using a mathematical model based on the thresholds, irradiation parameters for 532-, 730-, 755-, 785-, and 1064-nm picosecond laser treatments were evaluated quantitatively.

STUDY DESIGN/MATERIALS AND METHODS

A suspension of melanosomes extracted from porcine eyes was irradiated using picosecond lasers with varying fluence. The mean particle size of the irradiated melanosomes was measured by dynamic light scattering, and their disruption was observed by scanning electron microscopy to determine the disruption thresholds. A mathematical model was developed, combined with the threshold obtained and Monte Carlo light transport to calculate irradiation parameters required to disrupt melanosomes within the skin tissue.

RESULTS

The threshold fluences were determined to be 0.95, 2.25, 2.75, and 6.50 J/cm² for 532-, 730-, 785-, and 1064-nm picosecond lasers, respectively. The numerical results quantitatively revealed the relationship between irradiation wavelength, incident fluence, and spot size required to disrupt melanosomes distributed at different depths in the skin tissue. The calculated irradiation parameters were consistent with clinical parameters that showed high efficacy with a low incidence of complications.

CONCLUSION

The wavelength-dependent thresholds for melanosome disruption were determined. The results of the evaluation of irradiation parameters from the threshold-based analysis provided numerical indicators for setting the clinical endpoints for 532-, 730-, 755-, 785-, and 1064-nm picosecond lasers.

Comparison of 1064-nm and Dual-Wavelength (532/1064-nm) Picosecond-Domain Nd:YAG Lasers in the Treatment of Facial Photoaging: A Randomized Controlled Split-Face Study

BACKGROUND AND OBJECTIVES

To compare the efficacy and safety of 1064-nm and dual-wavelength (532/1064 nm) picosecond Nd:YAG lasers with a holographic optic in the treatment of facial photoaging.

STUDY DESIGN/MATERIALS AND METHODS

In this prospective, randomized split-face study, each half of each participant's face was randomly treated with a 1064-nm or 532/1064-nm picosecond laser. All participants underwent five treatment sessions and follow-up visits 1 and 3 months after the final treatment. The primary outcomes were measured as the global photoaging scores, determined by two physicians who were blinded to the treatments. The secondary outcomes were the participant-assessed Global Aesthetic Improvement Scale (GAIS) and satisfaction scores. Histopathological examinations were performed.

RESULTS

Global photoaging scores decreased significantly after treatment with either laser. The global photoaging scores, GAIS scores, and satisfaction scores did not differ significantly between the 1064-nm and 532/1064-nm picosecond laser treatments. Histological changes were similar between the two groups. Intraepidermal vacuoles and dermal hemorrhaging were observed immediately and 24 h after treatment. After five treatments, neocollagenesis was observed in the upper dermis of both groups, and elastic fibers were more elongated and orderly.

CONCLUSIONS

Treatments with 1064-nm and 532/1064-nm picosecond Nd:YAG lasers were comparably effective at improving photodamaged facial skin by remodeling the collagen and elastin network through laser-induced optical degradation and vascular damage.

Q-switched 532 nm Nd:YAG laser therapy for physiological lip hyperpigmentation: novel classification, efficacy, and safety

BACKGROUND

Physiological lip hyperpigmentation (PLH) is a common cosmetic concern in the Middle East and Asia. It is characterized by homogeneous symmetric diffuse hyperpigmentation affecting both lips. There is no satisfactory treatment for this condition. The aim of this study is to evaluate the efficacy and safety of Q-switched (QS) 532 nm Nd:YAG laser for PLH.

METHODS

A total of 30 patients with clinical diagnosis of PLH were retrospectively reviewed and included in the study. Patients underwent at least one laser treatment using QS 532 nm with a minimum follow up of six months. Laser parameters were as follows: spot size 2-3 mm, pulse duration 20 ns, fluence 2-4 J/cm². One to three sessions were performed depending on clinical response. Two methods were used for assessment: patient satisfaction and independent physician assessment. PLH was classified as grade 1 (upper lip fully affected plus only border of lower lip), grade 2 (upper lip fully affected plus most of lower lip), and grade 3 (majority of both lips hyperpigmented).

RESULTS

Excellent (>75% improvement) response was achieved in 30% of patients. Good (51-75% improvement) response was seen in 37% and 43% of patients according to patient satisfaction and independent physician assessment, respectively. Majority of patients required only one treatment session. Reactivation of herpes labialis occurred in two patients, and mottled hypopigmentation in three patients. None of the patients developed persistent hyperpigmentation or scarring.

CONCLUSIONS

PLH can be effectively treated with QS 532 nm Nd:YAG laser and is well tolerated by patients.