Detection of Keratoconus With a New Biomechanical Index (original) (raw)
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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...
Eye and vision (London, England), 2016
Keratoconus is a bilateral, non-inflammatory, degenerative corneal disease. The occurrence and development of keratoconus is associated with corneal thinning and conical protrusion, which causes irregular astigmatism. With the disruption of the collagen organization, the cornea loses its shape and function resulting in progressive visual degradation. Currently, corneal topography is the most important tool for the diagnosis of keratoconus, which may lead to false negatives among the patient population in the subclinical phase. However, it is now hypothesised that biomechanical destabilisation of the cornea may take place ahead of the topographic evidence of keratoconus, hence possibly assisting with disease diagnosis and management. This article provides a review of the definition, diagnosis, and management strategies for keratoconus based on corneal biomechanics.
Keratoconus diagnosis using Corvis ST measured biomechanical parameters
Journal of Current Ophthalmology, 2017
Purpose: To assess the diagnostic power of the Corneal Visualization Scheimpflug Technology (Corvis ST) provided corneal biomechanical parameters in keratoconic corneas. Methods: The following biomechanical parameters of 48 keratoconic eyes were compared with the corresponding ones in 50 normal eyes: time of the first applanation and time from start to the second applanation [applanation-1 time (A1T) and applanation-2 time (A2T)], time of the highest corneal displacement [highest concavity time (HCT)], magnitude of the displacement [highest concavity deformation amplitude (HCDA)], the length of the flattened segment in the applanations [first applanation length (A1L) and second applanation length (A2L)], velocity of corneal movement during applanations [applanation-1 velocity (A1V) and applanation-2 velocity (A2V)], distance between bending points of the cornea at the highest concavity [highest concavity peak distance (HCPD)], central concave curvature at the highest concavity [highest concavity radius (HCR)]. To assess the change of parameters by disease severity, the keratoconus group was divided into two subgroups, and their biomechanical parameters were compared with each other and with normal group. The parameters' predictive ability was assessed by receiver operating characteristic (ROC) curves. To control the effect of central corneal thickness (CCT) difference between the two groups, two subgroups with similar CCT were selected, and the analyses were repeated. Results: Of the 10 parameters compared, the means of the 8 were significantly different between groups (P < 0.05). Means of the parameters did not show significant difference between keratoconus subgroups (P > 0.05). ROC curve analyses showed excellent distinguishing ability for A1T and HCR [area under the curve (AUC) > 0.9], and good distinguishing ability for A2T, A2V, and HCDA (0.9 > AUC > 0.7). A1T reading was able to correctly identify at least 93% of eyes with keratoconus (cut-off point 7.03). In two CCT matched subgroups, A1T showed an excellent distinguishing ability again. Conclusions: The A1T seems a valuable parameter in the diagnosis of keratoconic eyes. It showed excellent diagnostic ability even when controlled for CCT. None of the parameters were reliable index for keratoconus staging.
Efficacy of corneal tomography parameters and biomechanical characteristic in keratoconus detection
Contact lens and anterior eye
Aim: To determine the efficacy of corneal thickness parameters and corneal biomechanical properties (CBPs) in discriminating between normal and keratoconus eyes. Method: After performing a comprehensive ophthalmic examination, 50 mild to moderate keratoconus and 50 age and sex matched myopic astigmatism eyes were prospectively included in the study. The corneal topographic maps and CBP were obtained by Pentacam and Ocular response analyser, respectively. Central corneal thickness (CCT), thinnest corneal thickness (TCT), corneal thickness (CT) and percentage thickness increase (PTI) at 1, 3 and 5 mm from the thinnest point and corneal volume (CV) at 3, 5, 7 and 10 centred on thinnest point, corneal hysteresis (CH) and corneal resistance factor (CRF) were recorded. Independent t-test and receiver operating characteristic (ROC) were done with SPSS software (version 15.0, SPSS, Inc.). Results: CCT, TCT, CT at 1, 3 and 5, CV at 3, 5, 7 and 10 mm, CH and CRF were significantly lower in keratoconus eyes compared to controls (p < 0.001). In addition, PTI at 1, 3 and 5 mm from the thinnest point showed significantly higher values in keratoconus group. ROC analysis demonstrated good predictive accuracy for cut-off point values. However, the centrally located indices had higher predictive accuracy compared to the peripherally located indices. Conclusion: Although good sensitivity and specificity were found for the mentioned parameters, the centrally located indices had higher predictive accuracy compared to peripherally located indices. It is suggested to use a combination of corneal pachymetry together with CBP for more accurate detection of keratoconus.
Biomechanics of corneal ectasia and biomechanical treatments
Journal of Cataract & Refractive Surgery, 2014
Many algorithms exist for the topographic/tomographic detection of corneas at risk for postrefractive surgery ectasia. It is proposed that the reason for the difficulty in finding a universal screening tool based on corneal morphologic features is that curvature, elevation, and pachymetric changes are all secondary signs of keratoconus and post-refractive surgery ectasia and that the primary abnormality is in the biomechanical properties. It is further proposed that the biomechanical modification is focal in nature, rather than a uniform generalized weakening, and that the focal reduction in elastic modulus precipitates a cycle of biomechanical decompensation that is driven by asymmetry in the biomechanical properties. This initiates a repeating cycle of increased strain, stress redistribution, and subsequent focal steepening and thinning. Various interventions are described in terms of how this cycle of biomechanical decompensation is interrupted, such as intrastromal corneal ring segments, which redistribute the corneal stress, and collagen crosslinking, which modifies the basic structural properties. Financial Disclosures: Proprietary or commercial disclosures are listed after the references. J Cataract Refract Surg 2014; -:---Q 2014 ASCRS and ESCRS Q 2014 ASCRS and ESCRS Published by Elsevier Inc.
The Role of Corneal Biomechanics for the Evaluation of Ectasia Patients
International Journal of Environmental Research and Public Health, 2020
Purpose: To review the role of corneal biomechanics for the clinical evaluation of patients with ectatic corneal diseases. Methods: A total of 1295 eyes were included for analysis in this study. The normal healthy group (group N) included one eye randomly selected from 736 patients with healthy corneas, the keratoconus group (group KC) included one eye randomly selected from 321 patients with keratoconus. The 113 nonoperated ectatic eyes from 125 patients with very asymmetric ectasia (group VAE-E), whose fellow eyes presented relatively normal topography (group VAE-NT), were also included. The parameters from corneal tomography and biomechanics were obtained using the Pentacam HR and Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany). The accuracies of the tested variables for distinguishing all cases (KC, VAE-E, and VAE-NT), for detecting clinical ectasia (KC + VAE-E) and for identifying abnormalities among the VAE-NT, were investigated. A comparison was performed considering th...
Understanding the Correlation between Tomographic and Biomechanical Severity of Keratoconic Corneas
BioMed Research International, 2015
Purpose. To evaluate correlation between tomographic gradation of keratoconus (KC) and its corresponding air-puff induced biomechanical response. Methods. Corneal tomography and biomechanics were measured with Scheimpflug imaging in 44 normal and 92 KC corneas. Deformation waveform was also analyzed with Fourier series. A custom KC severity scale was used from 1 to 3 with 3 as the most severe grade. Tomographic and biomechanical variables were assessed among the grades. Sensitivity and specificity of the variables were assessed using receiver operating characteristics (ROC). Results. Curvature variables were significantly different between normal and disease ( < 0.05) and among grades ( < 0.05). Biomechanical variables were significantly different between normal and disease ( < 0.05) but similar among grades 1 and 2 ( > 0.05). All variables had an area under the ROC curve greater than 0.5. The root mean square of the Fourier cosine coefficients had the best ROC (0.92, cut-off: 0.027, sensitivity: 83%, specificity: 88.6%). Spearman correlation coefficient was significant between most variables ( < 0.05). However, tomographic segregation of keratoconus did not result in concomitant biomechanical segregation of the grades. Conclusions. There was lack of significant biomechanical difference between mild disease grades, despite progressive corneal thinning. Mathematical models that estimate corneal modulus from air-puff deformation may be more useful.
Journal of refractive surgery (Thorofare, N.J. : 1995), 2017
To present a case series of patients with subclinical keratoconus with normal topometric (anterior curvature) and tomographic findings in one eye who showed abnormalities detected by Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) in vivo biomechanical assessment. All patients had a complete ophthalmic examination, including the Corvis ST biomechanical measurements, optical tomography, and pachymetry with Pentacam (Oculus Optikgeräte GmbH), and Placido-based topography with either the Nidek (OPD III Nidek, Gamagori, Japan) or CSO platform (Costruzione Strumenti Oftalmici, Florence, Italy). Inclusion criteria were a clinical diagnosis of ectasia in one eye and normal topometric and tomographic findings in the fellow eye (subclinical keratoconus), including a Belin/Ambrósio Enhanced Ectasia total deviation index from the Pentacam with less than 1.6 standard deviations from normative values and a Corvis Biomechanical Index score of greater than 0.5 in both eyes. Tomographic and t...
Turkish Journal of Ophthalmology, 2021
Objectives: To determine corneal biomechanical and tomographic factors associated with keratoconus (KC) progression. Materials and Methods: This study included 111 eyes of 111 KC patients who were followed-up for at least 1 year. Progression was defined as the presence of progressive change between the first two consecutive baseline visits in any single parameter (A, B, or C) ≥95% confidence interval or two parameters ≥80% confidence interval for the KC population evaluated by the Belin ABCD progression display. The eye with better initial tomographic findings was chosen as the study eye. Analyzed Pentacam parameters were maximum keratometry (Kmax), minimum pachymetry (Kmin), central corneal thickness, thinnest corneal thickness, 90° vertical anterior and posterior coma data in Zernike analysis, and Belin Ambrosio Enhanced Ectasia Display Final D value. Corneal hysteresis (CH) and corneal resistance factor (CRF) were analyzed together with the waveform parameters obtained with Ocular Response Analyzer (ORA). Factors related to KC progression were evaluated using t-tests and logistic regression tests. Statistical significance was accepted as p<0.05. Results: There were 44 (mean age: 27.1±8.5 years, female: 25) and 67 (mean age: 31.1±9.1 years, female: 36) patients in the progressive and non-progressive groups, respectively. Although Pentacam parameters along with CH and CRF were similar between the two groups, ORA waveform parameter derived from the second applanation signal p2area was statistically significantly lower in the progressive group (p=0.02). Each 100-unit decrease in p2area increased the likelihood of keratoconus progression by approximately 30% in the logistic regression analysis (β=0.707, p=0.001, model r2=0.27). Conclusion: Parameters derived from the second applanation signal of ORA may be superior to conventional ORA parameters and corneal tomography in predicting KC progression.