HIGH-FREQUENCY ULTRASOUND QUANTITATIVE-ANALYSES OF CORNEAL SCARRING FOLLOWING EXCIMER-LASER KERATECTOMY

Objective: To report objective grading and analysis of excimer laser-i nduced scarring using high-frequency ultrasound. Methods: High-frequen cy ultrasound (50 MHz) corneal examination was performed on eight New Zealand white rabbits at different time points (10, 17, 24, and 74 day s following phototherapeutic keratectomy). We used biometry and signal -processing techniques to determine corneal, epithelial, and scar thic knesses and to quantify the acoustic backscatter. Results: Excimer las er-induced scarring showed an irregularly distributed acoustic hyperre flectivity that decreased through day 74. Corneal thickness remained r educed after ablation (mean, 318 mum compared with 419 mum for control s). Epithelial thickness averaged 62 mum and scar thickness, 87 mum. S car peak and average anterior stroma acoustic backscatter ratios decre ased from day 10 to day 74 (19.65 to 2.76, and 6.42 to 1.32, respectiv ely). Histopathologic study showed increased keratocyte activity at ea rly time points that correlated with acoustic backscatter ratios and i maging pattern. Conclusions: High-frequency ultrasound signal processi ng is a noninvasive method that quantitatively grades excimer laser-in duced corneal scarring.