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Modern tonometers (Ocular Response Analyzer) can only show the presence of biomechanical disorders of the fibrous membrane, while elastotonometry reacts not only to their presence, but also to their type., Purpose: To build a mathematical model that would use elastotonometry to assess biomechanical properties of the eye in treatment of hyperopia with LASIK and FemtoLASIK surgeries., Material and Methods: The study included 64 operations: 34 FemtoLASIK surgeries, and 31 LASIK surgeries. All patients before and after surgery underwent standard examination necessary for keratorefractive surgery, including elastotonometry. The next step was the analysis of elastotonometry curves and eye finite element model in the software package Ansys (Ansys, Inc.; U.S.A.). During the analysis, the fibrous membrane was modeled by two spherical segments, which before elastotonometry were influenced only by true intraocular pressure (IOP). There was a problem of determining tonometric IOP when the cornea is pressured with flat bottomed loads during elastotonometry. It was taken into account that at the first stage of loading, the IOP was applied, and then the force corresponding to the weight of the tonometer. After tonometry, IOP increased so that the volume inside the composite membrane corresponded to the value before loading., Results: Mathematical modeling has shown that after surgical treatment of hyperopia, flexural stiffness of the cornea decreases, elevation of the elastotonometry curve increases, and the higher the true IOP, the greater the elevation. The greatest increase in lift due to increased IOP is observed after LASIK operation, while after FemtoLASIK this change is not significant, in which case the dependence of tonometric IOP on the weight of the load is almost linear., Conclusion: The obtained results allow for elastotonometry to be recommend for further medical research as a promising method for assessing biomechanical characteristics of the fibrous membrane of the eye.

Purpose: To compare the effectiveness, safety, predictability and stability of FemtoLASIK procedure in low to moderate myopia using Femto Visum and Femto LDV Z6 femtosecond laser platforms and to evaluate the effect of these procedures on corneal higher-order aberrations., Material and Methods: Russian femtolaser platform (1 MHz) was used to form the corneal flap in the main group consisting of 98 patients (98 eyes) with mean spherical equivalent (SE) of -3.73±1.42 D. Swiss femtolaser platform (5 MHz) was used in the control group (94 patients, 94 eyes; mean SE -3.81±1.44 D). Excimer laser ablation was performed using the Russian platform (500 Hz) in both groups. All patients underwent complete ophthalmological examination. The follow-up period was 12 months., Results: Twelve month postoperatively, in the '1 MHz' group uncorrected visual acuity (UCVA) of 1.0 or better was achieved in 91.8% of patients, and in the '5 MHz' group - in 90.4% (p>0.05). There were no registered losses of 2 or more lines of best-corrected visual acuity (BCVA) in either group. In the '1 MHz' group, predictability of targeted refraction within ±0.5 D was achieved in 91.8% of patients, within ±1.0 D - in 99.0%; in the '5 MHz' group - in 91.5% and 98.9% of patients, respectively (p>0.05). Root-mean-square (RMS) deviation of corneal higher-order aberrations in the 6-mm optical zone was increased by 0.072 μm (by 1.21 times) and by 0.077 μm (by 1.22 times) in the '1 MHz' and '5 MHz' groups (p>0.05), respectively., Conclusion: The FemtoLASIK procedures performed using Russian (1 MHz) and Swiss (5 MHz) femtosecond laser platforms are effective, safe, predictable, have stable postoperative visual and refractive outcomes, and lead to increase in RMS of corneal higher-order aberrations using both platforms in patients with low to moderate myopia. There were no statistically significant differences between the two femtolaser platforms (p>0.05) for all examined parameters.