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 picosecond laser keratomileusis (PLK) in the feline model with follow-up of up to 6 months. Design: The study design was a case-controlled, feline animal 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). The second eye of each cat was used as a control. Intervention: Picosecond laser keratomileusis, a new intrastromal laser technique with the neodymium-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 pachymetry, topography, tonometry, and biomicroscopic examination were performed before and after surgery at scheduled intervals for 6 months. Results: 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 difference in the thickness of the cornea at any timepoint (P >0.05). For 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 scar. With the slit-lamp examination, a faint, thin line of haziness barely was visible in the periphery of the flap. The histologic examination results showed no significant collagen disruption, inflammation, or endothelial irregularities comparing the control with the postoperative corneas. Conclusion: Myopic intrastromal PLK produces a refractive effect on the cornea that depends on the thickness of the lenticle removed and persists after 6 months with minimal stromal haze and no surgical complications. The authors' results, although encouraging, indicate the need for further studies to confirm the efficacy of PLK as a valid refractive procedure.