Optical transfer function in corneal topography for clinical contrast sensitivity analysis

Thomas Bende; Benedikt J. Jean M.D.; Theo Oltrup

doi:10.1117/12.387533

7 June 2000 Optical transfer function in corneal topography for clinical contrast sensitivity analysis

Thomas Bende, Benedikt J. Jean M.D., Theo Oltrup

Proceedings Volume 3908, Ophthalmic Technologies X; (2000) https://doi.org/10.1117/12.387533
Event: BiOS 2000 The International Symposium on Biomedical Optics, 2000, San Jose, CA, United States

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.

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Thomas Bende, Benedikt J. Jean M.D., and Theo Oltrup "Optical transfer function in corneal topography for clinical contrast sensitivity analysis", Proc. SPIE 3908, Ophthalmic Technologies X, (7 June 2000); https://doi.org/10.1117/12.387533

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KEYWORDS

Contrast sensitivity

Cornea

Phase shifts

Visualization

Optical aberrations

Optical transfer functions

Ray tracing

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