Optimized Distance Holders Improve Precision in Fractional Laser Treatment

Fractional Photothermolysis (FP) relies on precise laser focus to create microscopic treatment zones (MTZs). Focal plane deviations, caused by handpiece pressure and movement, shift the treated tissue out of focus, increasing spot size and reducing lesion depth, compromising treatment efficacy. This study investigates an optimized spacer to mitigate load-induced deviations and improve clinical outcomes.

A difference frequency generation (DFG) laser system (IPG Medical) with 3050/3200 nm wavelength treated ex vivo human abdominoplasty skin, mounted on a load-adjustable platform (0-1000 g, ±0.1 g). Tissue was treated at 5 mJ/pulse with a nominal spot size of 40 µm using spacers ranging from 2 × 2 mm² to 8 × 8 mm² and an optimized 2 × 2 mm² grid spacer. Optical coherence tomography measured skin bulging and focal plane deviations, while histological analysis validated lesion depth and diameter. Knife-edge technique projections were used to assess theoretical beam behavior.

Applied load caused skin bulging, resulting in a linear increase in lesion diameter and a linear decrease in depth. Smaller spacers (2 × 2 mm²) reduced focal deviations and maintained MTZ precision within the Rayleigh range. 2 × 2 mm² grid spacers further reduced bulging by redistributing the load and ensuring more uniform MTZ formation.

Load-induced focal shifts significantly impact FP efficiency, particularly on nonuniform skin surfaces. An optimized spacer enhanced precision by minimizing bulging, allowing treatments to remain within one Rayleigh length. These findings highlight the clinical importance of spacer selection in achieving consistent FP outcomes, particularly for small-spot laser applications. Clinicians should integrate smaller or grid-patterned spacers to enhance procedural accuracy.