Oestrogen-induced changes in biomechanics in the cornea as a possible reason for keratectasia

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Abstract
The risk of regression after photorefractive keratectomy (PRK) and the tendency to develop keratectasia after laser-assisted in situ keratomileusis (LASIK) procedure is higher in women than men. Currently, interest is focused on the influence of oestrogen on corneal stability after corneal refractive surgery. The aim of this experimental study was to investigate the change in biomechanical properties of the cornea induced by oestrogen. The influence of oestrogen was investigated in 12 fresh porcine corneas incubated in culture medium with 10 micromol/l beta-oestradiol for 7 days. A group of 12 porcine corneas incubated in culture medium without oestradiol for the same time served as a control group. Strips of cornea were cut and the stress-strain was measured in a biomaterial tester. The Young's modulus was calculated. During incubation the thickness of the cornea changed in the control group by only 6.4% and in the oestradiol group by 12%. However, the difference in the biomechanical stress values at 10% strain was significantly larger. In the control group the stress value was 120.18+/-28.93 kPa and in the oestradiol group 76.87+/-34.63 kPa (p = 0.002), representing a reduction of the corneal stiffness by 36% due to the oestradiol treatment. Oestrogen is a modulating factor of the biomechanical properties of the cornea that is not explainable only by an increased swelling. The significance of the hormone status of patients and its influence on the biomechanical stability of the cornea, a determining factor after refractive surgery, have been underestimated and may contribute to the development of keratectasia.

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