Impact and permanence of LASIK-induced structural changes in the cornea on pneumotonometric measurements: contributions of flap cutting and stromal ablation.
OBJECTIVE
To determine the factors that lead to changes in intraocular pressure (IOP) measurements after laser-assisted in situ keratomileusis (LASIK) and their long-term stability.


METHODS
Five hundred twenty-two myopic eyes and 296 hyperopic eyes were enrolled in the study. Pneumotonometry was used to measure IOP once in the preoperative stage and twice in the postoperative stage-1 month after the operation and 1 year later. Ultrasonic pachymetry was used to determine preoperative and intraoperative corneal thicknesses and axial length of the eye, whereas optical pachymetry was used in the preoperative stage and 1 month after surgery. Corneal topography was used to determine the preoperative and postoperative mean curvature of the anterior surface of the cornea over 3 and 5-mm diameter regions. Comparative statistical analysis of the retrospective data series was performed.


RESULTS
A highly significant reduction of IOP readings is found after LASIK for both myopic and hyperopic eyes. The reduction is stable 1 year after LASIK. In the case of myopic eyes, the reduction has a highly significant linear correlation with the amount of tissue ablated in the central region of the cornea.


CONCLUSIONS
Pneumotonometric IOP readings after LASIK are reduced, without recovering preoperative values even 1 year after surgery, because of flap cutting and tissue removal in the central region of the cornea. The contribution of flap cutting is estimated to be (1.6+/-0.8) mm Hg, whereas ablation contributes an additional (0.029+/-0.003) mm Hg/microm of removed tissue. This effect should be considered when evaluating the accuracy of IOP measurements in LASIK patients who are at risk for developing glaucoma.
Sánchez-Navés
Juan
J
Department of Physics Instituto Balear de Oftalmología, Ctra. La Vileta, Palma de Mallorca, Spain. juansanchez.naves@gmail.com
Furfaro
Luca
L
Piro
Oreste
O
Balle
Salvador
S
D000328:Adult; D003315:Cornea / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery*; D003319:Corneal Stroma / Q000601:surgery; D019781:Corneal Topography; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000503:physiopathology / Q000601:surgery; D007429:Intraocular Pressure / Q000502:physiology*; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery; D012189:Retrospective Studies; D013524:Surgical Flaps; D014065:Tonometry, Ocular; D014463:Ultrasonography