Experimental setup to determine the pulse energies and radiant exposures for excimer lasers with repetition rates ranging from 100 to 1050 Hz.
OBJECTIVE
To evaluate the feasibility of surface profiling for central ablation depth measurements and determine experimentally the required single-pulse energies and radiant exposures to achieve equivalent central ablation depths on bovine corneas for a myopic correction of -6.00 diopters (optical zone 6.5 mm) performed with laser repetition rates ranging from 100 to 1050 Hz.


METHODS
Institute for Refractive and Ophthalmic Surgery, Zurich, Switzerland, and WaveLight AG, Erlangen, Germany.


METHODS
Freshly enucleated bovine corneas and poly(methyl methacrylate) (PMMA) plates were photoablated. The shot pattern for the myopic correction was maintained during all experiments; the pulse laser energy was adjusted to achieve equal ablation depths for all repetition rates. Pulse energy, radiant exposure, and pulse duration were monitored to determine the required laser parameter.


RESULTS
The variations (standard deviation) of the profile measurements were +/-0.45 microm or less for PMMA and +/-1.50 microm or less for bovine corneas. Measurements with bovine corneas should be performed within 3 minutes or less to avoid larger variations in profile measurements. Increasing the repetition rate from 100 Hz to 1050 Hz required an increase in peak radiant exposure from 400 mJ/cm(2) to 530 mJ/cm(2) to achieve equal ablation for the myopic correction. The required increase in the mean radiant exposure ranged from 190 to 260 mJ/cm(2).


CONCLUSIONS
Higher-repetition-rate excimer lasers require increased radiant exposure. Further experimental studies should be performed to determine the relevance of spatial and temporal spot positioning, ablation-plume dynamics, and temperature increases during high-repetition-rate laser treatments.
Institute for Refractive and Ophthalmic Surgery, Swiss Federal Institute of Technology, Zurich, Switzerland. michael.mrochen@iroc.ch
Michael
M
Mrochen
Christian
C
Wuellner
Kristin
K
Rose
Christof
C
Donitzky
D000818:Animals; D002417:Cattle; D003315:Cornea / Q000528:radiation effects* / Q000601:surgery*; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer; D009216:Myopia / Q000601:surgery*; D011874:Radiometry / Q000379:methods; D014466:Ultraviolet Rays