Biomechanical Properties of Keratoconus Suspect Eyes (original) (raw)
Related papers
2019
Background To assess and compare corneal hysteresis (CH) and corneal resistance factor (CRF) in normal thin (NT) healthy corneas with central corneal thickness (CCT) 470-500 µm with matched thickness in keratoconus (KC) and keratoconus suspect (KCS) eyes. Methods A total of 66 eyes in three groups were included prospectively: NT, KCS and KC groups based on clinical examination and topography. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured by the ocular response analyzer. CH and CRF were compared between the three groups and statistically analyzed by variances test. Results The three groups consisted of 32 NT, 19 KCS, and 15 KC. The mean CH measured was 8.55± 1.77, 9.03± 1.119 and 8.06 ± 0.85 mm Hg in NT, KCS and KC eyes, respectively. The mean CRF was 8.39 ± 1.47, 8.27 ± 1.09 and 7.24 ± 1.27 mm Hg in NT, KCS and KC eyes, respectively. Within range of central corneal thickness (470 – 500 µm), only mean CRF was statistically significantly different between t...
Diagnostics in Ocular Imaging, 2020
A healthy cornea generates about 70% of the total eye refractive power of about 60 diopters [1]. Consequently, variations in biomechanical and geometrical properties of cornea can intensely affect corneal refractive power and may interrupt the eye vision. Evaluation of corneal biomechanical properties is essential for different ophthalmological operations such as refractive surgeries [2] and for accurate measurement of intraocular pressure (IOP) [3]. Changes in mechanical properties of the cornea result in corneal diseases, such as corneal ectasia, as well as cornea refractive problems [4]. So, evaluation of corneal material properties can be used as a beneficial tool for recognizing the corneal diseases such as keratoconus [5]. Moreover, accurate estimation of IOP makes detection of pathological diseases, such as glaucoma, more feasible [6]. Ocular Response Analyzer ® (ORA) is an older biomechanical evaluation device which evaluated intraocular pressure as well as corneal hysteresis (CH) and corneal resistance factor (CRF) as corneal biomechanical properties. Luce studied the results of ORA tonometry test to estimate biomechanical properties of the cornea and their relationship to IOP [7]. He expressed that corneal hysteresis measured by ORA provides valuable data for qualification of refractive surgery outcomes.
Combining Ocular Response Analyzer Metrics for Corneal Biomechanical Diagnosis
Journal of Refractive Surgery, 2013
orneal biomechanical evaluation could improve the safety of refractive surgery because many of today's cases of ectasia following LASIK are ascribed to undetected corneal biomechanical instability or subclinical keratoconus 1 (ie, corneas without the typical topography findings that develop manifest ectasia after years of follow-up). The detection of this increased susceptibility to postoperative ectasia has been greatly aided by imaging tools that analyze early corneal signs of keratoconus development such as anterior surface higher-order aberrations, 2 abnormal epithelial thickness, 3 pachymetric progression, 4 or posterior surface elevation. 5 There is nonetheless the possibility that a surgical candidate with ectasia propensity may consult before these morphological changes arise, especially considering the variable age of manifest keratoconus onset and its asymmetric development, 6 and thus a reliable method to assay corneal biomechanics might be able to uncover the stromal instability before the actual corneal morphology is modified by the ectatic process.
Evaluation of Ocular Biomechanical Indices to Distinguish Normal from Keratoconus Eyes
International Journal of Keratoconus and Ectatic Corneal Diseases, 2012
Purpose: To compare and assess the ability of pressure-derived parameters and corneal deformation waveform signal-derived parameters of the ocular response analyzer (ORA) measurement to distinguish between keratoconus and normal eyes, and to develop a combined parameter to optimize the diagnosis of keratoconus. Materials and methods: One hundred and seventy-seven eyes (177 patients) with keratoconus (group KC) and 205 normal eyes (205 patients; group N) were included. One eye from each subject was randomly selected for analysis. Patients underwent a complete clinical eye examination, corneal topography (Humphrey ATLAS), tomography (Pentacam Oculus) and biomechanical evaluations (ORA Reichert). Differences in the distributions between the groups were assessed using the Mann-Whitney test. The receiver operating characteristic (ROC) curve was used to identify cutoff points that maximized sensitivity and specificity in discriminating keratoconus from normal corneas. Logistic regression was used to identify a combined linear model (Fisher 1.0). Results: Significant differences in all studied parameters were detected (p < 0.05), except for W2. For the corneal resistance factor (CRF): Area under the ROC curve (AUROC) 89.1%, sensitivity 81.36%, specificity 84.88%. For the p1area: AUROC 91.5%, sensitivity 87.1%, specificity 81.95%. Of the individual parameters, the highest predictive accuracy was for the Fisher 1.0, which represents the combination of all parameters (AUROC 95.5%, sensitivity 88.14%, specificity 93.17%). Conclusion: Waveform-derived ORA parameters displayed greater accuracy than pressure-derived parameters for identifying keratoconus. Corneal hysteresis (CH) and CRF, a diagnostic linear model that combines different parameters, provided the greatest accuracy for differentiating keratoconus from normal corneas.
Investigative Opthalmology & Visual Science, 2007
PURPOSE. To compare hysteresis, a novel measure of ocular rigidity (viscoelasticity) in normal and keratoconic eyes. METHODS. The study consisted of 207 normal and 93 keratoconic eyes. Eyes were diagnosed as keratoconic based on clinical examination and corneal topography. The hysteresis was measured by the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY). The data were recorded by Generation 3 software for the ORA. Central corneal thickness (CCT) was measured with a handheld ultrasonic pachymeter in the midpupillary axis. RESULTS. The mean hysteresis was 10.7 Ϯ 2.0 (SD) mm Hg (range, 6.1-17.6) in normal eyes compared with 9.6 Ϯ 2.2 mm Hg (range, 4.7-16.7) in keratoconic eyes. The difference was statistically significant (P Ͻ 0.0001, unpaired t-test). Mean CCT in the normal and keratoconic eyes was 545.0 Ϯ 36.4 m (range, 471-650) and 491.8 Ϯ 54.7 m (range, 341-611), respectively; the difference was significant (P Ͻ 0.0001, unpaired t-test). CONCLUSIONS. Hysteresis was significantly higher in normal than in keratoconic eyes. It may be a useful measurement in addition to CCT, when assessing ocular rigidity, and may be of particular importance when trying to correct intraocular measurements for increased or decreased ocular rigidity. Long-term studies of change in hysteresis may provide information on the progression of keratoconus.
Corneal Biomechanical Metrics and Anterior Segment Parameters in Mild Keratoconus
Ophthalmology, 2010
Purpose: To compare corneal hysteresis (CH), corneal resistance factor (CRF), spherical equivalent (SE), average central keratometry (K-Avg), corneal astigmatism (CA), corneal volume (CV), anterior chamber (AC) depth, and central corneal thickness (CCT) between patients with mild keratoconus and healthy controls and to estimate the sensitivity and specificity of CH and CRF in discriminating mild keratoconus from healthy corneas.
Clinical and Experimental Optometry, 2009
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.
Biomechanical diagnostics of the cornea
Eye and Vision
Corneal biomechanics has been a hot topic for research in contemporary ophthalmology due to its prospective applications in diagnosis, management, and treatment of several clinical conditions, including glaucoma, elective keratorefractive surgery, and different corneal diseases. The clinical biomechanical investigation has become of great importance in the setting of refractive surgery to identify patients at higher risk of developing iatrogenic ectasia after laser vision correction. This review discusses the latest developments in the detection of corneal ectatic diseases. These developments should be considered in conjunction with multimodal corneal and refractive imaging, including Placido-disk based corneal topography, Scheimpflug corneal tomography, anterior segment tomography, spectral-domain optical coherence tomography (SD-OCT), very-high-frequency ultrasound (VHF-US), ocular biometry, and ocular wavefront measurements. The ocular response analyzer (ORA) and the Corvis ST ar...