Biomechanical properties of the cornea measured by the Ocular Response Analyzer and their association with intraocular pressure and the central corneal curvature

Abstract

Background:The aim of this study was to investigate the biomechanical properties of the cornea and their association with intraocular pressure (IOP), central corneal thickness (CCT) and the central corneal radius of curvature (Rc). Methods: Eighty-three eyes were divided into two groups. The biomechanical properties of the cornea were measured in 63 normal eyes and in 20 post-laser in situ keratomileusis (LASIK) eyes. The IOP, corneal hysteresis (CH) and corneal resistance factor (CRF) were measured by the Ocular Response Analyzer (ORA). The Rc and CCT were measured using the corneal topographer Medmont E-300 and the Tomey SP-100 Handy ultrasonic pachymeter. Other parameters measured by the ORA, such as TimeIn and TimeOut, were also studied. Results: A mean corneal hysteresis of 10.8 mmHg and CRF of 10.6 mmHg were recorded for the normal eyes. There was no significant association with central curvature. All parameters measured by the ORA showed a significant correlation with the CCT, except for the corneal-compensated intraocular pressure (IOPcc). Both IOPs measured by the ORA had the same values for the mean CH and CRF. For the post-LASIK eyes, the CH and CRF were lower than in the normal non-operated eyes. The TimeIn and the TimeOut also presented lower values for the post-LASIK eyes, suggesting that additional data can be obtained with the ORA measurements. Conclusions:The results of this study indicate that there is no correlation between the parameters measured with the Ocular Response Analyzer and central corneal radius of curvature. Some of the biomechanical properties of the cornea studied were found to differ in the normal eyes compared to the post-LASIK eyes.

Relationship of Structural Characteristics to Biomechanical Profile in Normal, Keratoconic, and Crosslinked Eyes

“…8,16 In normal eyes, CH and CRF are known to be influenced by the corneal thickness, being higher in thicker corneas probably because of increased collagen. 17 Some studies have reported on corneal structural parameters affecting CH and CRF in normal eyes 3,4,17,18 ; however, few studies have reported on keratoconic and crosslinked KC eyes. 11,16,19 The Pentacam is a rotating Scheimpflug camera (Oculus Inc, Wetzlar, Germany) that is routinely used for evaluating the cornea and diagnosing keratoconus.…”

“…The ORA uses a rapid air impulse and an advanced electro-optic system to assess changes in the corneal shape in response to indentation. 3 The corneal hysteresis (CH) and the corneal resistance factor (CRF) are the main biomechanical parameters derived through this deformation process. CH is a measure of corneal tissue properties that result from viscous damping, and CRF indicates the overall resistance of the cornea.…”

An Analytical Approach to Corneal Mechanics for Determining Practical, Clinically-Meaningful Patient-Specific Tissue Mechanical Properties in the Rehabilitation of Vision

“…These ranges were chosen in order to cover a very wide of possible inputs, including very extreme pathological conditions. [12][13][14]30,38 superior-inferior and nasal-temporal meridians with a sinusoidal fashioned density distribution as reported in literature [8,11]. The present modeling, if adapted to account for orthotropic reinforcement, may also be valuable for anticipating the patient-specific biomechanical limits of safe rehabilitating refractive surgery, in order to avoid unexpected iatrogenic keratoectatic catastrophic results.…”

“…However, the range of inputs that are permitted include severe pathological conditions and therefore this does not impose any clinical limitations (for the analysis and values please see the appendix). [12][13][14]30,38 Further improvements to this model may include adding orthotropic characteristics of the cornea in order to provide a more complete representation of corneal biomechanics. In the present framework it would be straight forward to do so by adding fiber elements in reinforced directions.…”

“…These ranges were chosen in order to cover a very wide of possible inputs, including very extreme pathological conditions. [12][13][14]30,38 The asterisk in Fig. 9 marks the values of the reference simulation (Fig.…”