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K. Huang, S. Iyengar, R. Radecki, A.M. Mahmoud, M.D. Twa, R.G. Lembach, C.J. Roberts; Comparison of Corneal Scattering Properties Pre– and Post–LASIK Using Orbscan Images . Invest. Ophthalmol. Vis. Sci. 2006;47(13):573.
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Compare corneal scattering properties before and after LASIK using contrast information from Orbscan II slit images.
A preliminary retrospective analysis was performed on 10 eyes of 5 subjects randomly selected from a larger group who received LASIK in a controlled trial, treated with either a Bausch & Lomb laser, or a VISX S3.1 Two Orbscan II exams were acquired from each eye pre–operatively and at one day, one week, one month, three months, and six months post–operatively. Each set of 40 Orbscan slit images per exam were submitted to a custom image processing system that was developed for this study. In order to avoid the artifacts induced by specular points in the image, only the slits that are not affected by the specular points and are close to the pupil (the slits number 11 to 17 and 31 to 37) are used. This image processing system automatically segments the corneal scattering slits based on a pre–defined intensity threshold and an automatic boundary tracing procedure. It then calculates the averaged pixel intensity value for the segmented corneal slits as an indicator for corneal scattering properties (the larger the number, the higher the scattering). The mean of the averaged intensity value for the two exams performed on the same day are used as the measurement for that day. The mean values are then denoted as I0, I1, I2, I3, I4, and I5 with I0 being the value for pre–operative exams and the rest are for the post–operative exams. The changes of the values with respect to I0 are then calculated as an indicator for the change of corneal scattering property.
For the tested eyes, the change in average slit pixel intensity values are 10.7%±2.8% (one day post–operation), 5.9%±7.0% (one week), 4.9%±2.4% (one month), 3.2%±3.8% (three months) and –2.1%±2.8% (six months).
The scattering properties of cornea increased around 10% after LASIK operation but then decreased and eventually reached a level less than that of pre–operation within six months. We are expanding our preliminary study to a database containing information from the full dataset of thirty patients. 1. Twa M, Lembach R, Bullimore M, Roberts C: "A Prospective Randomized Clinical Trial of Laser In–Situ Keratomileusis Using Two Different Lasers." American Journal of Ophthalmology, 2005; 140(2):173–8.
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