Histological and clinical evaluation of facial resurfacing using a carbon dioxide laser with the computer pattern generator.

Abstract

To delineate the extreme precision and uniformity of tissue ablation with a carbon dioxide laser using the computer pattern generator (CPG) (Coherent Laser Corp, Palo Alto, Calif) and to determine the ideal treatment parameters for uniform tissue ablation with minimal tissue thermal injury. Also, to evaluate postoperative healing of patients undergoing laser resurfacing compared with the traditional modalities of chemical peels and dermabrasion. A 3-part study was designed to demonstrate the effectiveness of this new modality. Cutaneous tissue from patients undergoing rhytidectomy was treated with a carbon dioxide laser with the CPG varying the treatment parameters. A histological analysis was completed to evaluate the uniformity of tissue ablation and thermal effect. Next, 30 tissue specimens were treated with identical power settings and evaluated histologically to determine the depth of tissue ablation, the variability in depth of ablation, and the degree of thermal effect on the underlying dermis. Finally, a prospective clinical analysis of patients undergoing facial resurfacing with the carbon dioxide laser was undertaken to determine the length of time required for reepithelialization, as well as resolution of postresurfacing erythema. Seventy-four patients underwent facial resurfacing with a carbon dioxide laser with CPG. Sixty patients were treated for cosmetic procedures and 14 were treated for either chronic acne scarring or posttraumatic scarring. To evaluate the CPG parameters, skin specimens were treated with the same fluence while the density setting varied from 1 through 9. To evaluate tissue uniformity and thermal effect, the CPG was used with the same treatment parameters of 300 mJ and a density of 5 for all specimens. Patients undergoing clinical evaluation were treated for periorbital, perioral, or full face resurfacing. All patients were treated by the same surgeon. Histological specimens were evaluated with light microscopy and hematoxylin-eosin staining to determine the depth and uniformity of ablation and the thermal effect. Patients were followed up after the procedure and evaluated for complete reepithelialization and resolution of erythema. A histological evaluation revealed that a treatment parameter of 300 mJ with a density setting of 3, 4, or 5 resulted in uniform ablation of the epidermis with minimal thermal injury to the underlying dermis. At density settings of 1 and 2, irregular ablation of the tissue occurred, while at a density setting of 6 through 9, increasing degrees of thermal injury and tissue necrosis occurred. The depth of epithelial ablation with density set at 5 varied between 65 and 90 microns (average depth, 78 microns). The thermal effect in the papillary dermis varied between 0 and 45 microns (average, 28 microns). No tissue necrosis was seen. Complete reepithelialization occurred an average of 7 days following the procedure, with resolution of cutaneous erythema occurring at an average of 42 days. The carbon dioxide laser with the CPG is an effective modality for cutaneous exfoliation. With the proper treatment parameters, extreme accuracy and uniformity of tissue ablation can be achieved. The tissue is ablated with micrometer accuracy and minimal thermal effect to the underlying dermis. Postoperative healing is comparable to that of the traditional modalities of dermabrasion and chemical peel. Postresurfacing erythema is transient and resolved in all patients.