Purchase this article with an account.
T Bende, R Berret, B Jean; Assessment of Selective Corneal Aberrations after treatment with different laser systems . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2041.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Optical quality (aberration) of the cornea is -besides visual acuity- an important criterion for the success of corneal refractive surgery. The main part of aberration is located at the transition air/tear film with the highest difference for the refractive indices. In this study the Functional Optical Zone (FOZ) after PRK for myopia correction with the Summit Apex Plus (Summit Technologies, USA) and the SCHWIND Keratron MultiScan (Schwind EyeTech, Germany) are compared. Methods: Based on the corneal height map obtained with a commercially available video topography system (C-Scan, MedRx, USA), the corneal image on a virtual retina is calculated by means of Ray-Tracing. Every point on the cornea is assigned a quality factor according to its image quality. The result is the Surface Quality Map (SQM), showing also the Functional Optical Zone (FOZ), defined by a quality factor above 95%. Extending the Point Spread Function (PSF) to a cosinus-function, contrast sensitivity of the cornea (Modular Transfer Function, MTF) can be assessed in analogy to conventional tests. Additionally the phase shift of an image relatively to the optical axis (Coma) can be calculated. In this study patients with myopic corrections between 1 and 9 D with a preoperative astigmatism of no more than 0.75D were analyzed. Treatment Zone Diameter (TZD) was 6.0 mm both for the Summit Apex Plus and the SCHWIND Keratron MultiScan. Results: The higher the amount of correction, the smaller the FOZ. Due to the different algorithms of the Summit Apex Plus and the SCHWIND Keratron MultiScan, the resulting FOZ for the Apex Plus is significantly smaller for the same amount of correction. Deterioration of contrast sensitivity and PSF with enlarging pupils starts -for a given amount of correction- earlier for corrections with the Summit Apex Plus than for the SCHWIND Keratron MultiScan. Conclusion: The aberration map, composed of the five described maps, 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", especially after refractive surgery. 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.
This PDF is available to Subscribers Only