Electron paramagnetic resonance spectroscopy of free radicals in corneal tissue following excimer laser irradiation.
OBJECTIVE
Free radicals, detected previously in corneal tissue following 193 nm laser irradiation, may be important agents in the laser/tissue interaction. Electron paramagnetic resonance spectroscopy (EPR) has been used to examine such radical formation in detail.


METHODS
Bovine corneal strips were frozen in liquid nitrogen, irradiated with excimer laser pulses, and assayed by EPR. Exposure conditions were varied to study radical formation dependence on laser intensity and repetition. Results were measured against a quantifiable standard to calculate radical quantum yield.


RESULTS
Either weak or intense laser fluences produced comparable tissue EPR signals. Radicals accumulated in frozen tissue for at least 10 initial ablation pulses. Radical quantum yield in cornea was 0.15%.


CONCLUSIONS
Corneal radical formation is largely a photochemical process driven by the 193 nm laser radiation. Reactive radical species are produced in substantial numbers and likely have a significant clinical role.
Pettit
G H
GH
Food & Drug Administration, Center for Devices & Radiological Health, Rockville, Maryland 20857, USA.
Ediger
M N
MN
Hahn
D W
DW
Landry
R J
RJ
Weiblinger
R P
RP
Morehouse
K M
KM
D000818:Animals; D002417:Cattle; D003315:Cornea / Q000378:metabolism* / Q000601:surgery*; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000378:metabolism; D054018:Lasers, Excimer; D010777:Photochemistry; D018903:Photorefractive Keratectomy
D005609:Free Radicals