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Proceedings Paper

Optical transfer function in corneal topography for clinical contrast sensitivity analysis
Author(s): Thomas Bende; Benedikt J. Jean M.D.; Theo Oltrup
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Paper Abstract

Customized ablation aiming to optimize visual acuity in refractive surgery requires objective data on corneal surface, like the contrast sensitivity. Fast ray tracing, using the high resolution 3-D elevation data in conjunction with Snell's law describe the diffraction of the incident rays and the resulting image on a 'virtual retina.' A retroprojection leads to a 'surface quality map.' For objective contrast sensitivity measurement a sinus (or cos) wave of different frequencies is used for a calculated projection in analogy to the clinical contrast sensitivity charts. The projection on the individual cornea surface is analyzed for the Modular Transfer Function (MTF) and the Phase Shift Function (PSF) as a function of frequencies. PSF, not yet clinically used, is a parameter to determine even minimal corneal tilt. The resulting corneal aberration map (CAM) as described here and applied to a 4.5 D PRK (OZD equals 6.5 mm) reveals that the area of minimal aberration measures only 4.2 mm. The CAM can likewise be used to describe the 'quality' of a laser system's ablation pattern based upon the area of minimal optical aberrations. The CAM only describes surface aberration with high resolution, an advantage over wave front sensing which measures all accumulated optical aberrations including the changing ones of the lens during accommodation and the transient ones due to lens aging and early cataract formation.

Paper Details

Date Published: 7 June 2000
PDF: 6 pages
Proc. SPIE 3908, Ophthalmic Technologies X, (7 June 2000); doi: 10.1117/12.387533
Show Author Affiliations
Thomas Bende, Univ. Eye Hospital Tuebingen (Germany)
Benedikt J. Jean M.D., Univ. Eye Hospital Tuebingen (Germany)
Theo Oltrup, Univ. Eye Hospital Tuebingen (Germany)

Published in SPIE Proceedings Vol. 3908:
Ophthalmic Technologies X
Pascal O. Rol; Karen Margaret Joos M.D.; Fabrice Manns, Editor(s)

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