Posterior corneal curvature changes after myopic laser in situ keratomileusis☆
Section snippets
Subjects
In this prospective nonrandomized (self-controlled) comparative trial, 57 otherwise healthy eyes (28 right, 29 left, 28 bilateral) of 14 women and 15 men were included that had been nonconsecutively treated by one surgeon (ES) from March 1998 to February 1999 with LASIK in the Centro Medico Docente La Trinidad, Caracas, Venezuela, for myopia (n = 35, −1.00 to −15.50 D, mean, −4.75 ± 3.07 D) or myopic astigmatism (n = 22, sphere 0.00 to −9.75 D, mean, −4.75 ± 2.36 D; cylinder −0.75 to −3.50 D,
Refractive outcome
All the LASIK procedures were uneventful. At 3 months postoperatively, the SEQ ranged from −2.00 to 1.00 (mean, −0.24 ± 0.58) D. For pure myopia, it ranged from −2.00 to 1.00 (mean, −0.19 ± 0.52) D; for myopic astigmatism, it ranged from −2.00 to 1.00 (mean, −0.32 ± 0.69) D (sphere −2.00 to +1.00 D, mean, −0.24 ± 0.72 D; cylinder −0.25 to −0.75 D, mean, −0.50 ± 0.13 D). In eyes with RBT ≤250 μm, it ranged from −2.00 to 1.00 (mean −0.04 ± 0.87) D; in eyes with RBT >250 μm, it ranged from −2.00
Potential and limitations of the orbscan topography/pachymetry system
With conventional Placido-disc technology, the cornea is illuminated by a set of concentric mires, which are reflected off the cornea and imaged by a video camera positioned at the videokeratoscope axis, and the deformation of the mires is used for calculation of anterior corneal curvature. In contrast, the Orbscan is a pancorneal slit-scanning-topography system in which two scanning slit lamps project 40 calibrated beams onto the eye, angled at 45° to the left and to the right of the video
Conclusions
The ability to individually assess the posterior corneal curvature may have important practical value for the detection of mild iatrogenic keratectasia after lamellar keratorefractive surgery. Increased negative keratometric diopters that did correlate well with the amount of intended correction and the residual bed thickness and oblate asphericity of the posterior corneal curvature suggest that mild “keratectasia” of the cornea may be common early after LASIK. Further studies are required to
Acknowledgements
The authors thank Anja Feuerlein for entering data into the database.
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The authors have no proprietary interest in the development or marketing of this or any competing instrument or piece of equipment.