3 (05) 2016

Comparative analysis of determining of cornea biomechanical properties at keratoconus by using different methods

Shargorodskaya I. V.

P. L. Shupyk National Medical Academy of Postgraduate Education, Kyiv, Ukraine 

 Resume. The problem of the clinical studies of biomechanical properties and structures of the eye tissue has a long history, but still far from being solved. Measurement of corneal hysteresis (CH) using the analyzer cornea biochemical properties ocular response analyzer (ORA) became the world standard in the evaluation of the cornea biomechanical properties. Considerable achievements of last years in modern diagnostics and treatment of keratoconus have not removed an urgency of the given problem from the agenda as long as traditional notions about pathogenesis of the keratoconus not always allow to struggle effectively with this difficult and continuously progressing disease.

 Purpose. To carry out a comparative analysis of the measurements of corneal biomechanical parameters at keratoconus by using different methods.

Materials and methods. The 24 patients (48 eyes) with keratoconus were included in investigation. In the control group were included 20 patients (40 eyes) with emmetropic refraction. The corneal biomechanical parameters were carried out in the same patients by the use the comparative analysis between the measurements obtained of a well-known method in the evaluation ORA, the elastotonometry, module for monitoring Belin/Ambrosio ectasia (BAD) of chamber Oculus Pentacam device Sheimpflug by a standard technique and the indicators calculated with using way offered by us and the device for estimation of cornea rigidity in vivo. 

Results. It was registered the considerable advantages of using the developed new way and the device for estimation of cornea rigidity in vivo in comparison with ORA, elastotonometry, keratotopographic on Sheimpflug camera Oculus Pentacam which allowed not only to reveal presence of biomechanical infringements of cornea at keratoconus, but also to differentiate their character. The factor is developed for the description of change degree of biomechanical properties of cornea in vivo it was worked out the coefficient of cornea rigidity. Increase of coefficient of corneal rigidity (K_ER) above (+)6.4 % may serve as a criterion for progression of keratoconus. 

 Conclusions. Loading tests allow receive more exact information on biomechanical properties of cornea in comparison with standard researches on ORA, elastotonometry and Sheimpflug camera Oculus Pentacam.

 Keywords: keratoconus, cornea, biomechanical properties, coefficient of cornea rigidity, elastotonometry, ORA, Oculus Pentacam.

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Received: 13 May 2016

Published: December 2016

Corneal biomechanical parameters, corneal sensitivity: small-incision lenticule extraction versus femtosecond laser-assisted laser in situ keratomileusis

Mokbel T. H.¹, Ghanem A. A.¹, Mady S. A.², El-Emam D. S.<sup>1

1</sup>Mansoura Ophthalmic Center, Faculty of Medicine, Mansoura University, Mansoura, Egypt
²Ophthalmology Department, Faculty of Medicine, Benha University, Benha, Egypt

Purpose. To compare the biomechanical properties of the cornea and corneal sensitivity after small-incision lenticule extraction (SMILE group) with those after femtosecond laser-assisted laser in situ keratomileusis (femto-LASIK group).

Materials and methods. One hundred and fifty patients (80 eyes and 70 eyes) that received SMILE and femto-LASIK procedures, respectively, were enrolled prospectively in this study. Corneal biomechanical properties such as corneal hysteresis (CH), corneal resistance factor (CRF), P1 area, and P2 area were quantitatively assessed with the Ocular Response Analyzer. Corneal sensitivity was quantitatively assessed with the Cochet – Bonnet esthesiometry. All eyes assessed preoperatively, 1 week, and 1, 3, 6 and 12 months postoperatively.

Results. The decrease in CH, CRF, P1 area, and P2 area was statistically significant one week postoperatively compared with preoperatively in both groups (P < 0.05). However, these values in the SMILE group were significantly higher than those in the femtoLASIK group 3 months, 6 months, 12 months postoperatively (P < 0.05). Both SMILE and femto-LASIK eyes demonstrated impaired central corneal sensitivity and tear-film break up time immediately after both procedures. Central corneal sensitivity and tearfilm break up time values in the SMILE group were significantly higher than those in the femto-LASIK group 3 months, 6 months, 12 months postoperatively (P < 0.05). There were statistically significant correlations between the changes of postoperative central corneal ablation depth, and preoperative spherical equivalent at 12 months follow up in both groups (P < 0.05).

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