Optical comparison of multizone and single zone photo-refractive keratectomy

Purpose: To calculate and compare the point-spread function (PSF) and the central ablation depth (CAD) of a paraxial eye model after photo-refractive keratectomy (PRK), with single and multizone treatments. Method: A modified Le Grand- El Hage paraxial eye model, with a pupil diameter ranging from 2 to 8 mm was used. Ray-tracing was performed for initial myopia ranging from 1 to 10D; after single zone PRK; after double zone PRK; and after triple zone PRK. The ray-tracing of a parallel incident beam was calculated by using the paraxial matrix method. Results: At equal CAD, the optical image quality is better after single zone treatments. Conclusion: Multizone treatments do not seem to be advantageous optically.