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


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.
Litton-TASC, San Antonio, TX 78228, USA.
Robert J
RJ
Thomas
Gary D
GD
Noojin
David J
DJ
Stolarski
Rebecca T
RT
Hall
Clarence P
CP
Cain
Cynthia A
CA
Toth
Benjamin A
BA
Rockwell
D000818:Animals; D005131:Eye Injuries / Q000473:pathology; D053685:Laser Therapy / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods*; D007834:Lasers; D023421:Models, Animal; D011323:Primates; D012160:Retina / Q000473:pathology* / Q000601:surgery*; D012449:Safety / Q000592:standards