Oe. Hanuch et al., MYOPIC PICOSECOND LASER KERATOMILEUSIS WITH THE NEODYMIUM-YTTRIUM LITHIUM-FLUORIDE LASER IN THE CAT CORNEA, Ophthalmology, 105(1), 1998, pp. 142-149
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.