EXCIMER-LASER CALIBRATION SYSTEM

Citation
Jd. Gottsch et al., EXCIMER-LASER CALIBRATION SYSTEM, Journal of refractive surgery, 12(3), 1996, pp. 401-411
Citations number
18
Categorie Soggetti
Ophthalmology,Surgery
ISSN journal
1081597X
Volume
12
Issue
3
Year of publication
1996
Pages
401 - 411
Database
ISI
SICI code
1081-597X(1996)12:3<401:ECS>2.0.ZU;2-E
Abstract
BACKGROUND: Excimer laser photoablation for refractive and therapeutic keratectomies has been demonstrated to be feasible and practicable. H owever, corneal laser ablations are not without problems, including th e delivery and maintenance of a homogeneous beam. We have developed an excimer laser calibration system capable of characterizing a laser ab lation profile. METHODS: Beam homogeneity is determined by the analysi s of a polymethylmethacrylate (PMMA)based thin-film using video captur e and image processing. The ablation profile is presented as a color-c oded map. Interpolation of excimer calibration system analysis provide s a three-dimensional representation of elevation profiles that correl ates with two-dimensional scanning profilometry. Excimer calibration a nalysis was performed before treating a monkey undergoing phototherape utic keratectomy and two human subjects undergoing myopic spherocylind rical photorefractive keratectomy. Excimer calibration analysis was pe rformed before and after laser refurbishing. RESULTS: Laser ablation p rofiles in PMMA are resolved by the excimer calibration system to .006 mu m/pulse. Correlations with ablative patterns in a monkey cornea we re demonstrated with preoperative and postoperative keratometry using corneal topography, and two human subjects using videokeratography. Ex cimer calibration analysis predicted a central-steep-island ablative p attern with the VISX Twenty/Twenty laser, which was confirmed by corne al topography immediately postoperatively and at 1 week after reepithe lialization in the monkey. Predicted central steep islands in the two human subjects were confirmed by videokeratography at 1 week and at 1 month, Subsequent technical refurbishing of the laser resulted in a be am with an overall increased ablation rate measured as microns/pulse w ith a donut ablation profile. A patient treated after repair of the la ser electrodes demonstrated no central island. CONCLUSIONS: This excim er laser calibration system can precisely detect laser-beam ablation p rofiles. The calibration system correctly predicted central islands af ter excimer photoablation in a treated monkey cornea and in two treate d human subjects. Detection of excimer-laser-beam ablation profiles ma y be useful for precise calibration of excimer lasers before human pho torefractive and therapeutic surgery.