gms | German Medical Science

102. Jahrestagung der DOG

Deutsche Ophthalmologische Gesellschaft e. V.

23. bis 26.09.2004, Berlin

Functional optical zone (FOZ) for different laser systems

Meeting Abstract

  • corresponding author K. Berret - University Eye Hospital Tübingen, Dept. I, DEOS
  • W. Vega - University Eye Hospital Tübingen, Dept. I, DEOS
  • T. Oltrup - University Eye Hospital Tübingen, Dept. I, DEOS
  • T. Bende - University Eye Hospital Tübingen, Dept. I, DEOS
  • B. Jean - University Eye Hospital Tübingen, Dept. I, DEOS

Evidenzbasierte Medizin - Anspruch und Wirklichkeit. 102. Jahrestagung der Deutschen Ophthalmologischen Gesellschaft. Berlin, 23.-26.09.2004. Düsseldorf, Köln: German Medical Science; 2004. Doc04dogFR.08.09

The electronic version of this article is the complete one and can be found online at:

Published: September 22, 2004

© 2004 Berret et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.




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 three different laser systems.


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%. In this study 298 eyes with myopic corrections (PRK) between -0.75 and -10.0 D and a Treatment Zone Diameter of 6.5 mm are analyzed.


The higher the amount of ametropia corrected, the higher the reduction of the FOZ. An association was also found between the reduction of the FOZ and the change of Best Spectacle Corrected Visual Acuity (BSCVA). Reduction of the FOZ for a given amount of correction was comparable for the three laser systems. No correlation was found between preoperative FOZ and preoperative degree of ametropia or BSCVA.


The Surface Quality 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 will help predicting potential problems after refractive surgery under mesopic conditions.