MYOPIC PICOSECOND LASER KERATOMILEUSIS WITH THE NEODYMIUM-YTTRIUM LITHIUM-FLUORIDE LASER IN THE CAT CORNEA

Objective: The study aimed to evaluate the effects of myopic picosecon d laser keratomileusis (PLK) in the feline model with follow-up of up to 6 months. Design: The study design was a case-controlled, feline an imal model. Participants: The procedure was completed in 1 eye each of 12 cats divided into 3 groups (group 1, sham operation; group 2, 100- mu m lenticle thickness; and group 3, 150-mu m lenticle thickness). Th e second eye of each cat was used as a control. Intervention: Picoseco nd laser keratomileusis, a new intrastromal laser technique with the n eodymium-yttrium lithium fluoride picosecond laser, was presented. The procedure, analogous to laser keratomileusis in situ, consists of two lamellar ring cuts and one vertical ring-shape cut that define a 4-mm -diameter intrastromal lenticle. Main Outcome Measures: Corneal pachym etry, topography, tonometry, and biomicroscopic examination were perfo rmed before and after surgery at scheduled intervals for 6 months. Res ults: The mean (+/-standard deviation) diopter change for group 2 was 5.4 +/- 3.2 diopters at 1 month and remained stable during the 6-month period. For group 3, the change was 8.1 +/- 0.22 diopters at 1 month and 6.8 +/- 1.5 diopters at 6 months. Group 1 (sham operation) did not show significant diopter change compared with that of control eyes at any timepoint. Pachymetry results for group 1 showed no significant d ifference in the thickness of the cornea at any timepoint (P >0.05). F or groups 2 and 3, the corneal thickness was reduced significantly by 1 month (P <0.05), but it regressed to nearly preoperative values at 3 months. At 6 months, the corneas were clear with no grossly visible s car. With the slit-lamp examination, a faint, thin line of haziness ba rely was visible in the periphery of the flap. The histologic examinat ion results showed no significant collagen disruption, inflammation, o r endothelial irregularities comparing the control with the postoperat ive corneas. Conclusion: Myopic intrastromal PLK produces a refractive effect on the cornea that depends on the thickness of the lenticle re moved and persists after 6 months with minimal stromal haze and no sur gical complications. The authors' results, although encouraging, indic ate the need for further studies to confirm the efficacy of PLK as a v alid refractive procedure.