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B. A. Fink, A. Fisher, G. L. Mitchell, R. M. Hill; Thickness Maps: Site-Referenced Comparisons of Normal and Keratoconic Corneas. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1835.
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To develop four types of site-referenced full thickness corneal maps of five standard locations each, and to compare those maps both graphically and statistically for differences between normal and keratoconic corneas.
Ultrasound pachymetry (1640 M/s) measurements (8/site/cornea) were made at five locations (central and four positions 3 mm from that site) as a pilot study on 12 eyes, six from normal subjects and six from keratoconic eyes manifesting at least one of the physical indications of keratoconus as well as keratometric values between 45 and 52 D. Repeated measures analyses was used to compare thicknesses between locations between normal and keratoconic corneas.
In addition to a (1) center-referenced map (all mid-peripheral thicknesses were ratioed to that location) for the normal corneas, that same center-referenced format (2) was generated for the keratoconic corneas, and also (3) with the keratoconic corneas being referenced to the normal corneal center thickness. The fourth map (4) was a direct site-to-site difference comparison made between normal and keratoconic corneas. All five keratoconic sites were found to be thinner than their normal corneal counterparts, but only the inferior corneal site was found to be statistically different (p<0.023).
The inferior site of the keratoconic cornea, when referenced to its keratoconic center, was found to be 97% as thick, but only 88% as thick when referenced to the normal corneal center. Oxygen uptake rates at those five sites for both corneal types are being correlated currently with corresponding corneal thicknesses.
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