ULTRAVIOLET SOLID-STATE LASER (213-NM) PHOTOREFRACTIVE KERATECTOMY - IN-VIVO STUDY

Background: The pulsed ultraviolet 213-nm solid-state laser has been d emonstrated as an alternative to the gas argon-fluoride 193-nm excimer laser for photorefractive keratectomy (PRK). The authors studied the clinical course and histopathologic changes occurring in rabbit cornea s after PRK with a 213-nm solid-state laser. Methods: The 213-nm outpu t of neodymium:YAG frequency-quintupled laser was used to create 5-mm optical zone ablations in seven pigmented rabbit corneas. The radiant exposure was 250 mJ/cm(2) delivered through a computer-controlled scan ning delivery system with a spot size of 0.5 mm. The target ablation w as 4.0 diopters with an estimated ablation depth of 40 mu m. A clinica l estimate of corneal epithelial healing and stromal haze was made at intervals over the 3-month study period. Animals were killed immediate ly after ablation, or at 10 days, 1 month, or 3 months after ablation. Corneal tissue was preserved for light microscopy and transmission el ectron microscopy at each study interval. Results: All corneas re-epit helialized within 10 days postoperatively. Anterior stromal haze was c linically visible at 3 days, increased until approximately 1 month, an d then gradually decreased over the succeeding 2 months. Residual sube pithelial haze was visible at 3 months. Results of histopathologic stu dy documented normal epithelium healing over time; the basement membra ne retained its regular thickness and hemidesmosomes were abundant at 3 months. The anterior stroma had an increased number of fibroblasts a t 10 days, many of which remained until 1 month. A mild, transient, ce llular reaction occurred throughout the thickness of the stroma and th e endothelium. Conclusion: Using the 213-nm ultraviolet solid-state la ser with a scanning delivery system, PRK shows a similar clinical cour se and histopathologic findings to the 193-nm excimer PRK study in rab bits. It is a clinically viable procedure for refractive surgery and r equires further human clinical trials to determine its efficacy.