Corneal biomechanical evaluation in healthy thin corneas compared with matched keratoconus cases

Abstract

Purpose: To evaluate and compare corneal hysteresis (CH) and corneal resistance factor (CRF) in healthy eyes with a central corneal thickness (CCT) ≤ 505 μm with CH and CRF in gender-, age-, and CCT-matched keratoconus cases, and to estimate the sensitivity and specificity of these parameters for discriminating between the two groups. Methods: Prospective, comparative case series. In total 46 eyes from 30 healthy patients with CCT ≤ 505 μm, and 42 eyes from 30 CCT-, gender-and age-matched keratoconus cases were enrolled. Biomechanical metrics (CH and CRF) were measured using the Ocular Response Analyzer (ORA) and then compared. A receiver operating characteristic (ROC) curve was used to identify cut-off points to maximize the sensitivity and specificity for discriminating between the groups. Results: The CCT was 485.96 ± 17.61 μm (range, 438 -505) in healthy thin corneas and 483.64 ± 16.19 μm (range, 452 -505) in keratoconus; p=0.5225. CH was 8.63 ± 1.23 mmHg (range, 5.95 -12.2) and 8.07 ± 1.17 mmHg (range, 4.9 -9.85), respectively; p=0.0312. CRF was 8.43 ± 1.29 mmHg (range, 5.45 -11.10) and 7.22 ± 1.34 mmHg (range, 4.7 -9.45), respectively; p<0.001. ROC curve analysis showed a poor overall predictive accuracy of CH (cut-off, 8.95 mmHg; sensitivity, 63%; specificity, 23.8%; test accuracy, 44.30%) and CRF (cut-off, 7.4 mmHg; sensitivity, 28.3%; specificity, 40.5%; test accuracy, 34.12%) for detecting keratoconus in the eyes studied. Conclusion: CH and CRF were statistically lower in keratoconus than in healthy thin corneas. However, CH and CRF offered very low sensitivity and specificity for discriminating the groups.Keywords: Cornea/physiology; Keratoconus; Corneal diseases; Biomechanics/physiology; Diagnostic techniques, ophthalmological RESUMOObjetivo: Avaliar e comparar a histerese corneana (CH) e o fator de resistência corneano (CRF) em olhos saudáveis com espessura corneana central (CCT) ≤ 505 μm com os resultados de CH e CRF em pacientes com ceratocone pareados por sexo, idade e CCT, além de estimar a sensibilidade e especificidade destes parâmetros na diferenciação dos grupos. Métodos: Estudo prospectivo, do tipo série de casos comparativa. No total, 46 olhos de 30 pacientes saudáveis com CCT ≤ 505 μm, e 42 olhos de 30 pacientes com ceratocone pareados por sexo, idade e CCT foram incluídos. Os parâmetros biomecânicos (CH e CRF) foram obtidos através do equipamento Ocular Response Analyzer (ORA) e depois comparados. Curvas ROC (Receiver operating characteristic) foram utilizadas para identificar o melhor valor de corte que apresentasse a maior sensibilidade e especificidade na discriminação entre ceratocone e córneas finas saudáveis para cada dado estudado. Resultados: A CCT encontrada foi 485,96 ± 17,61 μm (de 438 a 505) no grupo de córneas finas saudáveis e 483.64 ± 16,19 μm (de 452 a 505) no grupo ceratocone; p=0,5225. CH 8,63 ± 1,23 mmHg (de 5,95 a 12,2) e 8,07 ± 1,17 mmHg (de 4,9 a 9,85), respectivamente; p=0,0312. CRF 8,43 ± 1,29 mmHg (de 5,45 a 11,10) e 7,22 ± 1,34 mmHg (de 4,7 a 9,45), resp...

Evaluation of the anterior chamber angle in keratoconus and normal subjects

“…It follows that peripheral structural alterations and changes in the corneal curvature may modify its relative relationship to the uvea. The corneal ectasia, as one would expect and as is well documented [13][14][15] will demonstrate an anterior chamber depth that increases with KC. However, this finding does not describe the changes that may occur in the peripheral regions of the cornea in KC.…”

“…An evaluation of the anterior chamber angle in KC subjects is most frequently screened during biomicroscopy using van Herick's technique. However, this technique may induce errors since the anterior chamber depth may be influenced by localized apical protrusion and thinning which would increase the measured depth thus giving a false impression of the angle [13][14][15]. In cases of suspected narrow angles, the measurement can be more accurately determined using gonioscopy, which is a more invasive procedure for the ocular surface.…”

Implante de segmentos de anel estromal em ceratocone: resultados e correlações com a biomecânica corneana pré-operatória

“…Por exemplo, a indicação do crosslinking deve ser realizada para evitar a piora da visão, sendo fundamental uma propedêutica adequada para confirmar a indicação. Os avanços dos métodos diagnósticos em córnea, desde a topografia (23,54) até a tomografia com reconstrução 3-D, (25,26,55,56) o estudo biomecânico da córnea in vivo (29,(57)(58)(59)(60)(61) e a aberrometria ocular, (62)(63)(64) se destacam também para o planejamento cirúrgico.…”

Evaluation of Ocular Biomechanical Indices to Distinguish Normal from Keratoconus Eyes

“…Corneal hysteresis (CH) and the corneal resistance factor (CRF), which are the corneal biomechanical metrics generated by the ORA, have been the subjects of several recent publications. 3,4 Luce presented data (Luce D, ORA waveform analysis and beyond. Presented at: American Society of Cataract and Refractive Surgery Annual Meeting, April 3 to 8,2009; San Francisco, California) indicating that waveform parameters provided from the ORA signal may be more sensitive than CH or the CRF in discriminating abnormal corneas.…”