Mathematical models of picosecond laser keratomileusis for high myopia.
OBJECTIVE
Picosecond laser keratomileusis (PLK) is a refractive surgical procedure in which an intrastromal lenticle is created using the Nd:YLF picosecond laser and removed by lifting the anterior flap in the cornea. The purpose of this study was to assess the predictability of picosecond laser keratomileusis for high myopia.


METHODS
The results from a recent clinical series of non-sighted patients who had undergone picosecond laser keratomileusis with the Nd:YLF picosecond laser were retrospectively simulated with two mathematical models. In one model, the change in corneal curvature resulting from the collapse of a lenticular intrastromal cavity was predicted from a geometric analysis. A second model was developed using the finite element method. The results of both predictive models were compared to the clinical results at 1 and 6 months following surgery.


RESULTS
An average -13.30 D of flattening (range, -6.80 to -20.50 D) was measured at 6 months. The geometric model predicted an average correction of -23.10 D (range, -18.00 to -34.00 D), whereas the finite element model predicted an average curvature change of -17.40 D (range, -14.50 to -22.50 D). An average decrease in central pachymetry of 91 microm was measured at 6 months, as compared to a predicted decrease in thickness of 112 microm.


CONCLUSIONS
The outcome of picosecond laser keratomileusis for high myopia predicted using a finite element based model shows greater change in the corneal curvature and corneal thickness compared to clinical results. The relatively thick lenticules that are removed for high myopia cause considerable deformational changes in the cornea, which preclude the use of a purely geometric/optical approach for predicting the resultant corneal curvature changes.
Bryant
M R
MR
Doheny Eye Institute and Department of Ophthalmology, University of Southern California School of Medicine, Los Angeles, USA.
Marchi
V
V
Juhasz
T
T
D003315:Cornea / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D020342:Finite Element Analysis; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D008962:Models, Theoretical; D009216:Myopia / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D012189:Retrospective Studies; D014792:Visual Acuity