Effect of femtosecond laser energy level on corneal stromal cell death and inflammation.
OBJECTIVE
To analyze the effects of variations in femtosecond laser energy level on corneal stromal cell death and inflammatory cell influx following flap creation in a rabbit model.


METHODS
Eighteen rabbits were stratified in three different groups according to level of energy applied for flap creation (six animals per group). Three different energy levels were chosen for both the lamellar and side cut: 2.7 microJ (high energy), 1.6 microJ (intermediate energy), and 0.5 microJ (low energy) with a 60 kHz, model II, femtosecond laser (IntraLase). The opposite eye of each rabbit served as a control. At the 24-hour time point after surgery, all rabbits were euthanized and the corneoscleral rims were analyzed for the levels of cell death and inflammatory cell influx with the terminal uridine deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and immunocytochemistry for monocyte marker CD11b, respectively.


RESULTS
The high energy group (31.9+/-7.1 [standard error of mean (SEM) 2.9]) had significantly more TUNEL-positive cells in the central flap compared to the intermediate (22.2+/-1.9 [SEM 0.8], P=.004), low (17.9+/-4.0 [SEM 1.6], P< or =.001), and control eye (0.06+/-0.02 [SEM 0.009], P< or =.001) groups. The intermediate and low energy groups also had significantly more TUNEL-positive cells than the control groups (P< or =.001). The difference between the intermediate and low energy levels was not significant (P=.56). The mean for CD11b-positive cells/400x field at the flap edge was 26.1+/-29.3 (SEM 11.9), 5.8+/-4.1 (SEM 1.6), 1.6+/-4.1 (SEM 1.6), and 0.005+/-0.01 (SEM 0.005) for high energy, intermediate energy, low energy, and control groups, respectively. Only the intermediate energy group showed statistically more inflammatory cells than control eyes (P=.015), most likely due to variability between eyes.


CONCLUSIONS
Higher energy levels trigger greater cell death when the femtosecond laser is used to create corneal flaps. Greater corneal inflammatory cell infiltration is observed with higher femtosecond laser energy levels.
de Medeiros
Fabricio Witzel
FW
Cleveland Clinic, Cole Eye Institute, Ohio 44195, USA.
Kaur
Harmeet
H
Agrawal
Vandana
V
Chaurasia
Shyam S
SS
Hammel
Jefferey
J
Dupps
William J
WJ
Wilson
Steven E
SE
D000818:Animals; D017209:Apoptosis; D039481:CD11b Antigen / Q000378:metabolism; D002452:Cell Count; D003319:Corneal Stroma / Q000473:pathology* / Q000601:surgery; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D020287:In Situ Nick-End Labeling; D007249:Inflammation / Q000276:immunology / Q000473:pathology; D007634:Keratitis / Q000276:immunology / Q000473:pathology*; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer; D008856:Microscopy, Fluorescence; D009000:Monocytes / Q000276:immunology; D011817:Rabbits; D013524:Surgical Flaps
D039481:CD11b Antigen