Systematic free electron laser delivery of mid-infrared wavelengths to porcine corneas: Histologic analysis
Purpose: To evaluate histologically the ablative properties of the mid-infrared range of wavelengths on corneal tissue, with specific regard to dimensions of ablation and extent of collateral damage. Methods: Free electron laser (FEL) generated wavelengths of 2-9 to 7.0μm at powers of 5, 10 and 15mJ were systematically delivered to the corneas of freshly-enucleated porcine globes. Fluence = 0.75, 1.51 and 2.26J/cm2, respectively. Spot size = 60 × 70μm. Macropulse duration was 4.0μs with frequency of 10Hz; micropulse duration was 1.0ps with frequency of 2.8GHz. Treated corneas were embedded in paraffin for H&E-stained sections. Results: H&E-stained paraffin sections through ablation zones reveal small amounts (5-10μm) of damage collateral to ablations at 2.94 and 3.4μm wavelengths, while no collateral damage is apparent at 6.0μm. Ablations performed using other wavelengths in the 2.9 to 7.0μm range possess 20-100μm of collateral damage. Conclusions: 1. The mid-IR FEL-generated wavelength demonstrating the least collateral distortion coincided with the resonance frequency for the amide bond, 6.0/6.45μm. 2. Minimal collateral effects were noted at resonance frequencies for the OH bond, 2.94μm, and CH bond, 3.4μm. 3. Ablation at selected IR wavelengths corresponding to biochemical bond resonance frequencies may have keratorefractive applcations.
Vietorisz, EC; Rose, JG; Fowler, WC; Straub, KD; Barnett, GA; Proia, AD; Ross, JR; Iacobucci, MJ; Szarmes, EB; Plunkett, MA; Howell, DM
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