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P. Pillai, S. H. Yoo, W. Shi, J. Schiffman, R. K. Lee; LASIK Induces Temporal Changes in Corneal Hysteresis and Intraocular Pressure. Invest. Ophthalmol. Vis. Sci. 2008;49(13):649.
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Corneal hysteresis is believed to be an intrinsic viscoelastic property of the cornea. This study determines if corneal hysteresis (CH) and intraocular pressure (IOPg) is altered by LASIK surgery and how corneal wound healing after LASIK affects CH and IOPg over time.
Ninety eyes (56 right eyes and 34 left eyes) of 57 patients who were scheduled to undergo LASIK surgery to correct myopia were recruited for this IRB-approved study. Corneal hysteresis and intraocular pressure were measured using the Ocular Response Analyzer (Reichert, Depew NY) immediately prior to LASIK surgery, one day post-operatively and one month post-operatively. Central corneal thickness (measured by ultrasound pachymetry) and the degree of astigmatism before and after surgery (measured by Orbscan) were also assessed.
The mean corneal hysteresis one day after LASIK surgery was 8.85 (OD) and 9.13 (OS) whereas CH was 9.20 (OD) and 9.28 (OS) one month after LASIK. These post-operative CH values were significantly different from the mean pre-operative baseline CH of 10.64 (OD) and 10.52 (OS) (p-values < 0.001). The mean IOPg one day after LASIK surgery was 12.00 mm Hg (OD) and 12.35 mm Hg (OS) whereas IOPg was 10.64 mm Hg (OD) and 10.95 mm Hg (OS) one month after LASIK. These post-operative IOPg values were significantly different from the mean pre-operative baseline IOPg of 15.33 mm Hg (OD) and 15.26 mm Hg (OS) (p-values < 0.001).
LASIK ablation of corneal stroma decreases CH, demonstrating that CH is a modifiable property of the cornea. CH and IOPg are significantly decreased one day after LASIK surgery compared to the pre-operative values. Over the course of one month, CH increases significantly but does not return to its baseline value. This demonstrates that LASIK has a persistent effect on CH, possibly due to changes occuring during wound healing. Similarly, IOPg is decreased by LASIK surgery secondary to a measurement artifact of corneal thinning by LASIK.
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