Biomechanical Responses of Healthy and Keratoconic Corneas Measured Using a Noncontact Scheimpflug-Based Tonometer

Ali, Noor Q.; Patel, Dipika V.; McGhee, Charles N J

doi:10.1167/iovs.13-13715

Cited by 177 publications

(154 citation statements)

References 41 publications

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“…[13][14][15] The Corvis ST (Oculus Optikgeräte GmbH; Wetzlar, Germany) was later introduced as a noncontact tonometer, which monitors the response of the cornea to an air pressure pulse using an ultra-highspeed Scheimpflug camera, and uses the captured image sequence to produce estimates of IOP and deformation response parameters. 16 Several articles have recently been published on the possible applications of the Corvis ST, particularly evaluating possible biomechanical differences in the cornea after undergoing refractive surgery procedures, [17][18][19][20][21][22] between normal and keratoconic patients, [23][24][25][26] after cross-linking, 27 and in patients with glaucoma. [28][29][30][31] However, it has been demonstrated that IOP and pachymetry have important influences on most corneal biomechanical metrics provided by both the Corvis ST and ORA.…”

Section: Resultsmentioning

confidence: 99%

Influence of Pachymetry and Intraocular Pressure on Dynamic Corneal Response Parameters in Healthy Patients

et al. 2016

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n 1619, Scheiner provided the first precise description of the corneal shape using glass balls of known curvatures.1 From that first description, many other diagnostic tools have been developed to describe corneal shape, from keratometry to corneal topography (front surface curvature maps), 2 then into three-dimensional corneal tomography systems.3 More recently, it has been shown that corneal biomechanical behavior plays an important role in maintaining corneal shape, which is necessary for light refraction and clear vision, 4 and should therefore be considered in understanding the development of ectatic diseases 5,6 and the results of surgery. 4,7 Until recently, the evaluation of corneal biomechanical properties had been restricted to ex vivo laboratory studies 5,8 and mathematical corneal models. METHODS: Seven hundred five healthy patients were included in this multicenter retrospective study. The biomechanical response data were analyzed to obtain normative values with their dependence on corrected and clinically validated intraocular pressure estimates developed using the finite element method (bIOP), central corneal thickness (CCT), and age, and to evaluate the influence of bIOP, CCT, and age. RESULTS:The results showed that all DCRs were correlated with bIOP except deflection amplitude (DefA) ratio, highest concavity (HC) radius, and inverse concave radius. The analysis of the relationship of DCRs with CCT indicated that HC radius, inverse concave radius, deformation amplitude (DA) ratio, and DefA ratio were correlated with CCT (rho values of 0.343, -0.407, -0.444, and -0.406, respectively). The age group subanalysis revealed that primarily whole eye movement followed by DA ratio and inverse concave radius were the parameters that were most influenced by age. Finally, custom software was created to compare normative values to imported examinations.CONCLUSIONS: HC radius, inverse concave radius, DA ratio, and DefA ratio were shown to be suitable parameters to evaluate in vivo corneal biomechanics due to their independence from IOP and their correlation with pachymetry and age. The creation of normative values allows the interpretation of an abnormal examination without the need to match every case with another normal patient matched for CCT and IOP.[J Refract Surg. 2016;32(8):550-561.]

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Section: Resultsmentioning

confidence: 99%

Influence of Pachymetry and Intraocular Pressure on Dynamic Corneal Response Parameters in Healthy Patients

et al. 2016

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“…Most earlier studies produced an AUC lower than 0.900, [19][20][21] even though some of these studies refer to subclinical cases. 22 However, the dynamic Scheimpflug Corvis ST device is relatively new.…”

Section: Discussionmentioning

confidence: 99%

Detection of Keratoconus With a New Biomechanical Index

Vinciguerra¹,

Ambrósio²,

Elsheikh³

et al. 2016

J Refract Surg

409

346

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he early diagnosis of corneal ectasia is of foremost importance in both screening for refractive surgery and the early treatment of keratoconus. Topography or tomography analysis using either videokeratography or optical coherence tomography instruments can help detect alteration in the shape of the cornea such as thinning and increased curvature. However, these instruments cannot measure the mechanical stability, which is thought to be the initiating event of the disease, even before notable changes in corneal morphology take place.1,2 For this reason, there has been increasing interest in developing instruments to measure the in vivo biomechanical properties of the cornea to aid the diagnosis of an ectasia in a "biomechanical" stage, when topography and tomography are nor-T ABSTRACT PURPOSE: To evaluate the ability of a new combined biomechanical index called the Corvis Biomechanical Index (CBI) based on corneal thickness profile and deformation parameters to separate normal from keratoconic patients.METHODS: Six hundred fifty-eight patients (329 eyes in each database) were included in this multicenter retrospective study. Patients from two clinics located on different continents were selected to test the capability of the CBI to separate healthy and keratoconic eyes in more than one ethnic group using the Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany). Logistic regression was employed to determine, based on Database 1 as the development dataset, the optimal combination of parameters to accurately separate normal from keratoconic eyes. The CBI was subsequently independently validated on Database 2. RESULTS:The CBI included several dynamic corneal response parameters: deformation amplitude ratio at 1 and 2 mm, applanation 1 velocity, standard deviation of deformation amplitude at highest concavity, Ambrósio's Relational Thickness to the horizontal profile, and a novel stiffness parameter. The receiver operating characteristic curve analysis of the training database showed an area under the curve of 0.983. With a cut-off value of 0.5, 98.2% of the cases were correctly classified with 100% specificity and 94.1% sensitivity. In the validation dataset, the same cut-off point correctly classified 98.8% of the cases with 98.4% specificity and 100% sensitivity. CONCLUSIONS:The CBI was shown to be highly sensitive and specific to separate healthy from keratoconic eyes. The presence of an external validation dataset confirms this finding and suggests the possible use of the CBI in everyday clinical practice to aid in the diagnosis of keratoconus.[J Refract Surg. 2016;32(12):803-810.]

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“…3,4 The observation of the reduction in corneal hysteresis and corneal resistance factor values after LASIK and surface ablation has also been demonstrated. 5 This logically suggests that if CXL would significantly alter the biomechanics of progressive keratoconus corneas, these instruments would be able to identify changes.…”

Section: The Mystery Of Collagen Crosslinking When It Comes To In Vivmentioning

confidence: 93%

The Mystery of Collagen Cross-linking When it Comes to In Vivo Biomechanical Measurements

Gatinel¹

2014

J Refract Surg

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Biomechanical Responses of Healthy and Keratoconic Corneas Measured Using a Noncontact Scheimpflug-Based Tonometer

Cited by 177 publications

References 41 publications

Influence of Pachymetry and Intraocular Pressure on Dynamic Corneal Response Parameters in Healthy Patients

Influence of Pachymetry and Intraocular Pressure on Dynamic Corneal Response Parameters in Healthy Patients

Detection of Keratoconus With a New Biomechanical Index

The Mystery of Collagen Cross-linking When it Comes to In Vivo Biomechanical Measurements

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