Relationship between the biomechanical properties of the cornea and anterior segment measurements

OBJECTIVE: To evaluate the relationship of biomechanical properties, corneal hysteresis and corneal resistance factor with age, sex and various corneal parameters measured with a Pentacam in normal subjects. METHODS: A total of 226 eyes from 113 patients were enrolled in this study. The subjects underwent Ocular Response Analyzer and Pentacam evaluations. A varying-intercept multilevel regression was implemented using Bayesian inference. The predictor variables were age, sex, central corneal thickness, corneal volume at a 7-mm diameter, anterior chamber angle and volume, anterior chamber depth, mean radius of the corneal curvature and corneal astigmatism. RESULTS: Corneal hysteresis ranged from 5.5 to 14.8 mmHg (mean 10.42±1.74 mmHg), and the corneal resistance factor ranged from 5.7 to 15.5 mmHg (mean 10.23±1.88 mmHg). No predictor variable other than gender and central corneal thickness had a significant correlation with either corneal hysteresis or corneal resistance factor. Corneal hysteresis was positively associated with female sex and with central corneal thickness, and corneal resistance factor was positively associated with central corneal thickness. CONCLUSION: Despite the associations found, only a small fraction of the variance in biomechanical measurements could be explained by the descriptors that were evaluated, indicating the influence of other corneal aspects on the biomechanical characteristics.

Relationship between anterior segment and optic nerve head parameters in healthy subjects / Relações entre os parâmetros do segmento anterior e da cabeça do nervo óptico em indivíduos saudáveis

ABSTRACT Purpose: To determine the relationship between anterior segment and optic nerve head (ONH) parameters. Methods: Two hundred healthy subjects were enrolled in this study. The par­ticipants underwent measurement of anterior segment parameters with a Pentacam Scheimpflug system and imaging of the optic disc with confocal scanning laser ophthalmoscopy. Pearson's correlation coefficient was calculated to assess the associations between ONH and anterior segment parameters. Multivariate regression analyses controlling for age and disc area as confounding factors were also conducted. Results: There were significant negative relationships between optic disc area and corneal thickness (p=0.03, r=-0.217) and volume (p=0.017, r=-0.239). Corneal refractive power was significantly correlated with cup area, rim area, rim volume, and cup/disc ratio (p<0.05 for all). An increase of 1 diopter in anterior corneal refractive power corresponded to a decrease of 0.022 in cup/disc ratio. Rim volume was negatively correlated with anterior chamber depth and anterior chamber volume (p<0.05 for both). A 1-mm3 increase in anterior chamber depth corresponded to a 0.154-mm3 decrease in rim volume. Mean and maximum cup depth measurements were not associated with any of the anterior segment parameters. Conclusions: In nonglaucomatous eyes, the dimensions and shape of the ONH may be related to anterior segment morphology. Therefore, it may be helpful to take anterior segment parameters into consideration in evaluating the OHN.

RESUMO Objetivo: Determinar a relação entre os parâmetros do segmento anterior e da cabeça do nervo óptico (CNO). Métodos: Duzentos indivíduos saudáveis foram incluídos neste estudo. Os participantes foram submetidos à medição dos parâmetros do segmento anterior com o sistema Pentacam Scheimpflug e à obtenção de imagens de disco óptico com oftalmoscopia a laser de varredura confocal. O coeficiente de correlação de Pearson foi calculado para avaliar as associações entre CNO e os parâmetros do segmento anterior. Realizaram-se também análises de regressão multivariada que controlam a idade e a área do disco como factores de confusão. Resultados: Houve uma relação negativa estatisticamente significativa entre a espessura da córnea, o volume da córnea e a área do disco óptico (p=0,03, r=-0,217 e p=0,017, r=-0,239, respectivamente). As medições do poder de refração da córnea mostraram correlações significativas com a área da escavação, a área da rima, o volume da rima (RV) e a relação escavação/disco (C/D). (P<0,05 para todos). Um aumento de dioptria no poder de refração corneana anterior corresponde a uma diminuição de 0,022 em C/D. O RV mostrou correlação negativa com a profundidade da câmara anterior (PCA) e volume da câmara anterior. (P<0,05 para ambos). O aumento de 1 mm3 na PCA corresponde a uma diminuição de 0,154 mm3 no RV. As médias e as medidas máximas de profundidade de rima não mostraram associação com nenhum dos parâmetros do segmento anterior. Conclusões: Em olhos não glaucomatosos, as dimensões e forma da CNO podem estar relacionadas com a morfologia do segmento anterior. Portanto, pode ser útil levar em consideração os parâmetros do segmento anterior na avaliação da CNO.