Biomechanical and Tomographic Analysis of Unilateral Keratoconus (original) (raw)
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In-vivo corneal biomechanical analysis of unilateral keratoconus
International journal of ophthalmology, 2015
To evaluate and compare corneal biomechanical findings measured by ocular response analyzer, topographic and pachymetric findings in patients with unilateral keratoconus patients and healthy controls. This is an observational, case-control study. Patients with keratoconus in one eye and forme fruste keratoconus in the fellow eye were compared with sex and age matched with controls healthy subjects. All subjects were evaluated with rotating scheimpflug imaging system. The receiver-operating-characteristic curves were analyzed to evaluate the sensitivity and specificity of the parameters. Twenty-seven patients with keratoconus in one eye and forme fruste keratoconus in the fellow eye were compared with 40 eyes of 40 normal subjects. Corneal hysteresis (CH) was 8.0±1.7 mm Hg in keratoconus group, 8.3±1.6 mm Hg in forme fruste keratoconus group, and 9.8±1.6 mm Hg in control groups (P=0.54 between keratoconus and forme fruste keratoconus groups, P<0.01 between control group and other ...
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...
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.
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.
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.
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.
Peculiarities of Biomechanical Properties of Ocular Tissue in Keratoconus
Galician Medical Journal, 2016
Considerable achievements having been recently made in modern diagnostics and treatment of keratoconus have not diminished the urgency of the given problem as the traditional views of the pathogenesis of keratoconus do not always allow to struggle effectively with this difficult and continuously progressing disease.The objective of the research was to study the peculiarities of biomechanical properties of the cornea in keratoconus.Materials and methods. The article presents the analysis of studying biomechanical properties of the cornea in keratoconus. 44 patients (88 eyes) with keratoconus and emmetropic refraction were examined. To calculate biomechanical indicators of the cornea there was carried out the comparative analysis between the measurements obtained with the use of several methods in the same patients, namely the Oculus Pentacam-Scheimpflug imaging device by a standard technique and the indicators calculated using the method proposed by us and the device for in vivo esti...
Biomechanical Properties of Keratoconus Suspect Eyes
Investigative Opthalmology & Visual Science, 2010
PURPOSE. Measuring corneal biomechanical properties may help detect keratoconus suspect corneas and eliminate the risk of ectasia after LASIK. METHODS. Data of 504 eyes separated into three groups were retrospectively reviewed: normal (n ϭ 252), keratoconus suspect (n ϭ 80), and keratoconus (n ϭ 172). Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with an ocular biomechanics analyzer. RESULTS. Mean corneal hysteresis was 10.6 Ϯ 1.4 (SD) mm Hg in the normal group, compared with 10.0 Ϯ 1.6 mm Hg in the keratoconus suspect group and 8.1 Ϯ 1.4 mm Hg in the keratoconus group. The mean CRF was 10.6 Ϯ 1.6 mm Hg in the normal group compared with 9.7 Ϯ 1.7 in the keratoconus suspect group and 7.1 Ϯ 1.6 mm Hg in the keratoconus group. Mean CH and CRF were significantly different between the three groups (P Ͻ 0.001). CONCLUSIONS. CH and CRF alone cannot be used to identify keratoconus suspect corneas. Analyzing signal curves obtained with the biomechanics analyzer may provide additional valuable information for selecting qualified patients for refractive surgery.
Acta Ophthalmologica, 2013
Purpose: To evaluate the diagnostic capacity of the Ocular Response Analyser's keratoconus match index (KMI) and keratoconus match probability (KMP) classification in a sample of keratoconus (KC) patients. Methods: Keratoconus match index and KMP from 114 KC eyes, randomly selected from 114 patients with bilateral keratoconus (KCG), were compared with the corresponding ones from 109 normal eyes (CG). Keratoconus match index's predictive accuracy was assessed by receiver operating curves (ROC). Keratoconus match probability level of agreement was evaluated at the different KC stages of the Amsler-Krumeich classification. Correlations were estimated with topographic keratoconus classification (TKC), keratoconus index (KI), index of surface variance (ISV), vertical asymmetry (IVA), height asymmetry (IHA), height decentration (IHD), minimal radius (Rmin), central corneal thickness (CCT), thinnest corneal thickness (TCT) mean keratometry (Km) and intraocular pressure (IOPg). Results: Mean KMI in KCG and CG was 0.20 ± 0.38 and 0.98 ± 0.25, respectively (p < 0.01). Significant KMI differences (p < 0.01) were detected in different KC groups [range: 0.62 ± 0.38 (KC 1), )0.62 ± 0.04 (KC 4)]. Significant correlation was detected between KC staging and KMI (r = )0.56, p < 0.0001). Keratoconus match probability identified 22.03% of the CG eyes as suspect. Moreover, KMP identified 7.01% and 23.68% of the KCG eyes as normal and suspect, respectively. Receiver operating curves analysis for KMI parameter indicated a predictive accuracy of 97.7% (cut-off point: 0.512, sensitivity: 91.18%, specificity: 94.34%). Conclusions: Keratoconus match index seems to be a reliable index in keratoconus diagnosis and staging. Keratoconus match probability identifies a significant percentage of topographically defined KC and CG eyes as suspect. Diagnostic capacity of these novel indexes needs to be further explored.