Laser in situ keratomileusis flap stability during simulated aircraft ejection in a rabbit model.
OBJECTIVE
To determine the stability of the laser in situ keratomileusis (LASIK) flap in a rabbit model when subjected to vertical acceleration at nine times the force of gravity (+9 Gz) in an aircraft cockpit ejection simulator.


METHODS
Thirty-six eyes from 25 New Zealand white rabbits underwent LASIK flap creation without laser photoablation. One month after surgery, the rabbits were sedated and harnessed in a cockpit ejection seat simulator used to train United States Air Force pilots. They then underwent a controlled rapid-sequence ejection at +9 Gz. Subsequently, the rabbits were euthanized and the corneas harvested for microscopic examination. Refractive measurements and corneal examination were made before LASIK flap creation and prior to and after the +9 Gz ejections. Determination of LASIK flap dislocation was based on clinical observation of flap slippage or a significant shift in pre-ejection to postejection cylinder axis.


RESULTS
The average preoperative refraction of the rabbit eye was +1.83 D + 3.25 D x 086 degrees. The average change from pre-ejection to postejection was 0.04 D sphere, 0.02 D cylinder, 6.8 axis degrees, and 0.04 D spherical equivalent. The pre-ejection to postejection measurements were not statistically significantly different by a paired test. Laser in situ keratomileusis flap dislocation or ejection-induced corneal folds or striae were not clinically observed. Histologic examination revealed well-healed LASIK flaps but no reactive keratocytes at the central stromal-stromal interface.


CONCLUSIONS
Healed LASIK flaps as created in this rabbit model without laser ablation are stable when subjected to a rapid vertical ejection at nine times the force of gravity.
Goodman
Randall L
RL
Ophthalmology service, Mike O'Callaghan Federal Hospital, 99MDG/SGOSE, Nellis AFB, NV 89191, USA. rkgoodman@yahoo.com
Johnson
Daniel A
DA
Dillon
Harold
H
Edelhauser
Henry F
HF
Waller
Stephen G
SG
D000337:Aerospace Medicine; D000401:Aircraft; D000818:Animals; D003315:Cornea / Q000601:surgery*; D018471:Hypergravity / Q000009:adverse effects*; D020731:Keratomileusis, Laser In Situ; D008887:Military Medicine; D011183:Postoperative Complications / Q000503:physiopathology; D011817:Rabbits; D012449:Safety; D013524:Surgical Flaps; D014945:Wound Healing / Q000502:physiology*