Functional Optical Zone (FOZ) after Excimer LaserTreatment for Myopia

Abstract

Abstract: : Purpose: Optical quality (aberration) of the cornea is –besides visual acuity– an important criterion for the success of corneal refractive surgery. In this study the individually calculated values for the Functional Optical Zone (FOZ) are compared for two laser systems. Methods: Based on the corneal topography obtained with a commercially available video topography system (C–Scan), the corneal image on a virtual retina is calculated by a newly developed Windows–based software module by means of Ray–Tracing. The result is the Surface Quality Map (SQM), showing the Functional Optical Zone, being defined by a quality factor above 95%. 149 (74) eyes were treated with the Summit Apex+ (Schwind Keratom MultiScan) for a MRSE of in average –4.0±1.6 D (–4.0±1.8 D) with a range from –0.75 to –7.50 D (–0.75 to –8.50 D). Results: The higher the amount of correction, the smaller the FOZ. Due to different algorithms of the lasers used, the resulting FOZ may differ significantly for the same amount of correction. Conclusions: The aberration map is an important tool for the assessment of Selective Corneal Aberrations and the detection of the FOZ as the "real optical relevant diameter of correction" – in contrast to the treatment zone diameter. It allows qualifying and optimizing the algorithm of the laser system used. Furthermore together with a preoperative measurement of the pupil diameter it allows the prediction of potential problems after refractive surgery under mesopic conditions.

Keywords: refractive surgery: corneal topography • refractive surgery: optical quality • refractive surgery: PRK