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Proceedings Paper

Gel-modulated photo ablation using noncontact photoacoustic spectroscopy control: a new concept
Author(s): Benedikt J. Jean; Thomas Bende
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Paper Abstract

Refractive gels, applied on the corneal surface in situ act as laser beam modulators. Depending upon their surface shape and absorbency, they can be used to reshape irregular surfaces or induce refractive effects. Three gels (Palm I Pallikaris, Greece; Refrax 33, Imperial, USA; Biomask, Maverick USA) have been investigated using Non Contact Photoacoustic Spectroscopy (NCPAS). Their use requires on line detection and monitoring of the ablation process, indicating when the gel is ablated and the corneal tissue is exposed to the incident laser pulse. NCPAS enables this on line control. With the gels in their present form, stable ablation rates where achieved only after 200 - 400 pulses, depending upon the gel. The typical frequency shift of the Fourier -- transformed time signal of NCPAS, observed for different target materials (gels, human, and porcine cornea) allowed the discrimination of the different gels as well as from human and porcine corneal tissue (epithelium and stroma). NCPAS discriminates and identifies even those gels with similar ablation rates, using the typical frequency shift (difference >= 1 kHz). Refractive gels in combination with a powerful on-line control such as NCPAS has a potential to be used as a low cost approach for reducing or minimizing the amount of surface bound corneal optical aberrations; it could thus bypass the complexity and costs of corneal reshaping systems, using topography or wavefront based customized treatment algorithms.

Paper Details

Date Published: 7 June 2000
PDF: 7 pages
Proc. SPIE 3908, Ophthalmic Technologies X, (7 June 2000); doi: 10.1117/12.387534
Show Author Affiliations
Benedikt J. Jean, Univ. Eye Hospital Tuebingen (Germany)
Thomas Bende, Univ. Eye Hospital Tuebingen (Germany)


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

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