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Proceedings Paper

Femtosecond laser threshold: retinal damage versus induced breakdown mechanisms
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Paper Abstract

Threshold measurements at 90 femtoseconds (fs) and 600 fs have been made for minimum visible lesions (MVLs) using Dutch Belted rabbit and Rhesus monkey eyes. Laser induced breakdown (LIB) thresholds on biological materials including vitreous, normal saline, tap water, and ultrapure water are reported along with irradiance calculations utilizing nonlinear transmission properties including self-focusing. At both pulsewidths the ED50 dose required for the Rhesus monkey eye was less than half the value determined for the Dutch Belted rabbit eye, all thresholds being 1 microjoule ((mu) J) or less. Measurements on the Rhesus eye at 600 fs found the ED50 dose (0.26 (mu) J) to be much lower than the ED50 dose at 90 fs (0.43 (mu) J). But for these two pulsewidths, almost the same energy level was determined for the Dutch Belted rabbit eye (0.94 (mu) J vs. 1.0 (mu) J). LIB threshold measurements at 100 fs and 300 fs using a simulated eye with isolated vitreous found the ED50 dosages to be 3.5 and 6.0 (mu) J respectively. We found in all cases that the ED50 dosages required to produce MVLs in 24 hours for rabbit and monkey eyes were less than the ED50 values measured for LIB in vitreous or saline or any other breakdown values reported. Also observed was the fact that many of the threshold lesions did not appear in the 1-hour postexposure check but clearly showed up at the 24-hour reading which provided for a much lower threshold dose after 24 hours. We discuss the energy levels and peak powers at which nonlinear effects can begin to occur.

Paper Details

Date Published: 17 August 1994
PDF: 6 pages
Proc. SPIE 2134, Laser-Tissue Interaction V; and Ultraviolet Radiation Hazards, (17 August 1994); doi: 10.1117/12.182940
Show Author Affiliations
Clarence P. Cain, The Analytic Sciences Corp. (United States)
Cynthia A. Toth, Duke Univ. Eye Ctr. (United States)
Cindy D. Stein, Air Force Armstrong Lab. (United States)
Gary D. Noojin, The Analytic Sciences Corp. (United States)
David J. Stolarski, The Analytic Sciences Corp. (United States)
Benjamin A. Rockwell, Air Force Armstrong Lab. (United States)
Stephen A. Boppart, MIT (United States)
William P. Roach, Air Force Armstrong Lab. (United States)


Published in SPIE Proceedings Vol. 2134:
Laser-Tissue Interaction V; and Ultraviolet Radiation Hazards
Steven L. Jacques; David H. Sliney; Michael Belkin, Editor(s)

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