Femtosecond laser threshold: retinal damage versus induced breakdown mechanisms

Clarence P. Cain; Cynthia A. Toth M.D.; Cindy D. Stein; Gary D. Noojin; David J. Stolarski; Benjamin A. Rockwell; Stephen A. Boppart; William P. Roach

doi:10.1117/12.182940

17 August 1994 Femtosecond laser threshold: retinal damage versus induced breakdown mechanisms

Clarence P. Cain, Cynthia A. Toth M.D., Cindy D. Stein, Gary D. Noojin, David J. Stolarski, Benjamin A. Rockwell, Stephen A. Boppart, William P. Roach

Author Affiliations +

Proceedings Volume 2134, Laser-Tissue Interaction V; and Ultraviolet Radiation Hazards; (1994) https://doi.org/10.1117/12.182940
Event: OE/LASE '94, 1994, Los Angeles, CA, United States

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.

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Clarence P. Cain, Cynthia A. Toth M.D., Cindy D. Stein, Gary D. Noojin, David J. Stolarski, Benjamin A. Rockwell, Stephen A. Boppart, and William P. Roach "Femtosecond laser threshold: retinal damage versus induced breakdown mechanisms", Proc. SPIE 2134, Laser-Tissue Interaction V; and Ultraviolet Radiation Hazards, (17 August 1994); https://doi.org/10.1117/12.182940

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