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Proceedings Paper

Effect of spot size, ablation depth, and eye-tracker latency on the optical outcome of corneal laser surgery with a scanning spot laser
Author(s): Michael Bueeler; Michael Mrochen; Theo Seiler
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Paper Abstract

Based on eye movement data, we present a study on the effect of various laser and eye-tracking parameters on the optical outcome after scanning spot refractive surgery. Numerical simulations of the entire ablation process were performed on a schematic model eye under variation of the following parameters: ablation depth per pulse, laser spot size, eye tracker latency and magnitude of refractive correction. Three-dimensional ray tracing through an analytical model eye featuring the ablated corneal front surface enabled evaluation of the resulting optical quality. The modulation transfer function (MTF) was calculated to rate the difference in optical quality between an ideal (movement-free) treatment, and treatments performed with an eye-tracker working with a certain latency. For all the calculations it was assumed, that the laser repetition rate remains constant at 250 Hz. It was shown, that the contrast transfer can decrease significantly with increasing latency of the eye-tracker. For constant laser and tracking parameters, this decrease was found to be more significant for higher myopic corrections. It was further shown, that treatments performed with smaller spot sizes and smaller ablation depths per pulse are more sensitive to tracking latency. Assuming a certain eye tracker latency, the most stable results are obtained for large beam diameters and high central ablation depths per pulse. Latencies below 10 ms would allow for a reduction of the beam diameter to 0.50 mm as well as for ablation depths as small as 0.50 microns.

Paper Details

Date Published: 14 July 2003
PDF: 11 pages
Proc. SPIE 4951, Ophthalmic Technologies XIII, (14 July 2003); doi: 10.1117/12.488628
Show Author Affiliations
Michael Bueeler, Univ. of Zurich (Switzerland)
Swiss Federal Institute of Technology Zurich (Switzerland)
Michael Mrochen, Univ. of Zurich (Switzerland)
Swiss Federal Institute of Technology Zurich (Switzerland)
Theo Seiler, Institute for Refractive and Oculoplastic Surgery (Switzerland)

Published in SPIE Proceedings Vol. 4951:
Ophthalmic Technologies XIII
Fabrice Manns; Per G. Söderberg; Arthur Ho, Editor(s)

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