Multiphoton absorption is probably not the primary threshold damage mechanism for femtosecond laser pulse exposures in the retinal pigment epithelium

Randolph D. Glickman, Thomas E. Johnson

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Laser induced breakdown has the lowest energy threshold in the femtosecond domain, and is responsible for production of threshold ocular lesions. It has been proposed that multiphoton absorption may also contribute to ultrashort-pulse tissue damage, based on the observation that 33 fs, 810 nm pulse laser exposures caused more DNA breakage in cultured, primary RPE cells, compared to CW laser exposures delivering the same average power. Subsequent studies, demonstrating two-photon excitation of fluorescence in isolated RPE melanosomes, appeared to support the role of multiphoton absorption, but mainly at suprathreshold irradiance. Additional experiments have not found a consistent difference in the DNA strand breakage produced by ultrashort and CW threshold exposures. DNA damage appears to be dependent on the amount of melanin pigmentation in the cells, rather than the pulsewidth of the laser; current studies have found that, at threshold, CW and ultrashort pulse laser exposures produce almost identical amounts of DNA breakage. A theoretical analysis suggests that the number of photons delivered to the RPE melanosome during a single 33-fsec pulse at the ED 50 irradiance is insufficient to produce multiphoton excitation. This result appears to exclude the melanosome as a locus for two- or three-photon excitation; however, a structure with a larger effective absorption crosssection than the melanosome may interact with the laser pulses. One possibility is that the nuclear chromatin acts as a unit absorber of photons resulting in DNA damage, but this does not explain the near equivalence of ultrashort and CW exposures in the comet assay model. This equivalence indicates that multiphoton absorption is not a major contributor to the ultrashort pulse laser damage threshold in the near infrared.

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
EditorsS.L. Jacques, W.P. Roach
Pages162-172
Number of pages11
Volume5319
DOIs
StatePublished - 2004
EventProgress in Biomedical Optics and Imaging - Laser Interaction with Tissue and Cells XV - San Jose, CA, United States
Duration: Jan 26 2004Jan 28 2004

Other

OtherProgress in Biomedical Optics and Imaging - Laser Interaction with Tissue and Cells XV
CountryUnited States
CitySan Jose, CA
Period1/26/041/28/04

Keywords

  • Comet assay
  • DNA damage
  • Melanosome
  • Multiphoton absorption
  • RPE
  • Threshold
  • Ultrashort pulse laser

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Condensed Matter Physics

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