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Yu Kato, Hiroki Tanaka, Takako Tachikawa, Osamu Katsumi, Kazuhiko Ohnuma, Nobuaki Kitajima, Toru Noda; New Surgical Keratometry System for Toric Intraocular Lens Implantation: Comparison of Its Keratometric Readings to Preoperative Measurement by Corneal Topographer. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1378.
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To evaluate the clinical efficacy of a surgical keratometry system newly developed for toric intraocular lens implantation.
The keratometry unit was built on a surgical microscope and was comprised of a ring with 36 LED lamps to be projected onto the cornea and a fixation target lamp at the center of the ring. The image of the ring is reflected back through the optics of the surgical microscope, its distortion from the original circular shape is analyzed by developed software, and the astigmatic axis is indicated. The LED ring is as large as 106 mm in diameter and set in a retractable system 95 mm above the corneal surface, such that the circular image formed on the cornea is larger than conventional surgical keratometers. Ten eyes of 10 healthy individuals were tested while supine without using a lid speculum, and the results were compared to the astigmatic axes determined using the corneal topographer in the wavefront sensor (KR-1W, Topcon). Twenty eyes with a lid speculum in position at the beginning of the cataract surgery were tested, and the results were compared to the preoperative data in the same fashion.
The discrepancies in determined astigmatic axes between surgical keratometry and preoperative topography ranged from -0.4 to 0.9 degrees (mean, 0.7 degree; standard deviation, 0.7 degree) in eyes of healthy individuals without use of a lid speculum. The intraoperative measurements were less than 5 degrees in 17 eyes, 5 to 10 degrees in 2 eyes, and 18 degrees in 1 eye in which a lid-speculum was used.
This newly developed surgical keratometry system is highly accurate for determining the corneal astigmatic axes in eyes of supine patients without using a lid speculum; however, in clinical use, positioning a lid-speculum might substantially alter the corneal shape, indicating that the intraoperative keratometry has limited accuracy and that keratometry should be performed before placement of a lid speculum.
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