A comparative study of retinal effects from continuous wave and femtosecond mode-locked lasers

Lasers Surg Med. 2002;31(1):9-17. doi: 10.1002/lsm.10067.

Abstract

Background and objectives: In order to provide a direct comparison of the effects of mode-locked systems to those with continuous-wave (CW) or nonpulsed output, we have performed an experiment with lasers possessing otherwise identical output characteristics. This in vivo minimum visible lesion study compares retinal effects of mode-locked and CW lasers complete with histopathology of the treated areas.

Study design/materials and methods: Titanium:Sapphire lasers produced 800-nm output for either mode-locked (76 MHz repetition rate, 120 femtoseconds) or CW exposures. Alternating CW and mode-locked laser exposures were delivered to the paramacular retinal region of rhesus subjects. Laser exposure duration was set to one-quarter second for both types of exposures. Through ophthalmoscopic examination of the fundus, a minimal visible lesion (MVL) threshold for damage was established.

Results: Approximately 75 test sites for each type of exposure were examined. The laser dosage thresholds and 95% confidence intervals for minimal visible damage at 24 hours postexposure were found to be 5.9 mJ (5.23-6.6 mJ) and 5.84 mJ (5.23-6.58 mJ) for mode-locked and CW exposures, respectively.

Conclusions: Results are compared with published studies conducted at similar exposures. These nearly identical damage thresholds indicate a primarily thermal tissue damage mechanism. Comparative histopathology of acute and chronic lesions of both exposure types is also presented.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Eye Injuries / pathology
  • Laser Therapy / adverse effects*
  • Laser Therapy / instrumentation
  • Laser Therapy / methods*
  • Lasers
  • Models, Animal
  • Primates
  • Retina / pathology*
  • Retina / surgery*
  • Safety / standards