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First Author: Y.Novak RUSSIA
Co Author(s): L. Balashevich A. Kachanov
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To study how changes of corneal thickness influence on tonometric intraocular pressure indexes after Lasik operation, defined by Maklakov applanation tonometry and pneumotonometry.
St.-Petersburg Branch IR&TC Eye microsurgery named after academician S. Fyodorov, Saint-Petersburg, Russia.
The main group consisted of 460 patients (824 eyes) with myopia of low, medium and high degree, who were performed a standard Lasik operation using a modern high speed excimer laser MEL-80 ("Carl Zeiss Meditec"). Statistic analysis was made with the help of Statistica® program. All patients were gone through a standard ophthalmological examination before operation, which included IOP measurement using pneumotonometr, Maklakov tonometry, and keratopachimetry on A-scan/US - keratopachimetr DGH 5100 before Lasik operation and 1 year after.
We defined average pneumotonometry indexes and Maklakov applanation tonometry indexes, depending on the initial corneal thickness. In 41% of cases cornea had a usual thickness, and in 30% cornea was "thick". There was not only a statistically valid difference in pneumotonometry indexes between patients with different degree of corneal thickness, but also there was a difference of tonometric IOP by Maklakov in the same groups. On studying the changes in tonometric indexes after Lasik should be considered, that the rated ablation is often deeper than the actual one. So, real reduction of corneal thickness after Lasik was less than 15,6 + 6,8 mm of planned nomogram of excimer laser MEL-80. There was a statistically significant corneal thinning after Lasik performance, which made 71,5 + 33,3 mcm. Changes in sphere equivalent (SE) of refraction after Lasik operation has made 4,9+ 2,5 dptr . Postoperative changes in SE of refraction and corneal thickness correlated directly with decrease of tonometric IOP indexes (correlation r indexes exceeded 0,76). As we can see from the mentioned above information, it is obvious, that pneumotonometry indexes decreased on 5,9 + 2,1 mm Hg after Lasik, and that Maklakov"s tonometry indexes increased on 2,9 + 1,6 mm Hg.
1. Lasik operation in case of myopia leads to a statistically significant decrease of corneal thickness in its central part, and also leads to decrease of pneumotonometric IOP indexes by Maklakov. 2. In case of myopia, after Lasik operation pneumotonometric indexes change more than tonometric IOP indexes by Maklakov, but the last ones are statistically significantly decreasing in comparison with similar indexes before operation.