High-frequency ultrasound quantitative analyses of corneal scarring following excimer laser keratectomy.

OBJECTIVE: To report objective grading and analysis of excimer laser-induced scarring using high-frequency ultrasound. METHODS: High-frequency ultrasound (50 MHz) corneal examination was performed on eight New Zealand white rabbits at different time points (10, 17, 24, and 74 days following phototherapeutic keratectomy). We used biometry and signal-processing techniques to determine corneal, epithelial, and scar thicknesses and to quantify the acoustic backscatter. RESULTS: Excimer laser-induced scarring showed an irregularly distributed acoustic hyperreflectivity that decreased through day 74. Corneal thickness remained reduced after ablation (mean, 318 microns compared with 419 microns for controls). Epithelial thickness averaged 62 microns and scar thickness, 87 microns. Scar peak and average anterior stroma acoustic backscatter ratios decreased from day 10 to day 74 (19.65 to 2.76, and 6.42 to 1.32, respectively). Histopathologic study showed increased keratocyte activity at early time points that correlated with acoustic backscatter ratios and imaging pattern. CONCLUSIONS: High-frequency ultrasound signal processing is a noninvasive method that quantitatively grades excimer laser-induced corneal scarring.