Abstract: Objective To evaluate the impact of different CO₂ fractional laser parameters on the formation of microscopic treatment zone (MTZ) on the nail surface and to compare the observations of these areas using various instruments. Methods This study applied 60 different combinations of CO₂ fractional laser parameters, including pulse widths ranging from 100-1 000 μs and powers from 10-60 W, on bovine hoof samples. The formation and overall changes of MTZ on the nail surface were subsequently observed and compared using optical microscopy, inverted microscopy, and white light interferometry. The relationships between MTZ and various laser parameters were analyzed. Results Significant statistical differences were observed between white light interferometry and inverted microscopy in MTZ assessment(P＜0.001). White light interferometry demonstrated greater accuracy and reliability in measuring micro-ablative column(MAC) and thermal coagulation zone (TCZ). There were also significant statistical differences in MAC formation based on CO₂ fractional laser parameters(P＜0.001), with the strongest correlation found between pulse width and MTZ(0.656 68-0.772 62). Longer pulse widths correlated with larger MACareas and depths, as well as increased TCZ thickness. Conclusions White light interferometry shows significant advantages in assessing the impact of CO₂ fractional laser ablation on tissue depth. These findings provide valuable insights for optimizing laser parameters in the treatment of nail disorders and contribute to enhancing the safety and efficacy of such therapies.

Key words: CO₂ fractional laser, nail channel, thermal effect, white light interferometry