Influence of Anterior Biometry on Corneal Biomechanical Stiffness of Glaucomatous Eyes Treated With Chronic Medication or Filtration Surgery.
TL;DR: Evaluating corneal stiffness in primary angle-closure (PACG) and primary open-angle (POAG) glaucoma eyes that were subgrouped on the basis of the type of topical medication and filtration surgery using noncontact applanation found that medication or filTration surgery did not affect theCorneal biomechanical parameters differentially from nonglaucome eyes.
Abstract: PReCIS:: Anterior chamber depth, IOP, and thickness confounded the assessment of corneal biomechanical properties with noncontact applanation in glaucoma eyes. Compared with normal eyes, glaucoma eyes, which underwent long-term treatment or filtration surgery, had similar properties. Purpose The purpose of this study was to evaluate corneal stiffness in primary angle-closure (PACG) and primary open-angle (POAG) glaucoma eyes that were subgrouped on the basis of the type of topical medication and filtration surgery using noncontact applanation. Methods All eyes were retrospectively reviewed for intraocular pressure (IOP) with Corvis-ST (OCULUS Optikgerate Gmbh, Germany). Nonglaucoma (n=140), PACG (n=102 under medication), and POAG (n=154 under medication) eyes were included. Corneal stiffness was calculated using deformation amplitude and a biomechanical model. Multivariate analyses were performed, which evaluated the effect of systemic conditions (diabetes and hypertension), the effect of medication (prostaglandins or beta blockers or combined), and the effect of filtration surgery (PACG: n=23; POAG: n=26). Age, IOP, central corneal thickness (CCT), refractive error, and anterior chamber depth (ACD) were covariates. Results Diabetes and hypertension did not alter corneal stiffness of glaucoma eyes compared with nonglaucoma eyes (P>0.05). Corneal stiffness of POAG and nonglaucoma eyes was similar but significantly different from the stiffness of PACG eyes (P=0.002), irrespective of the type of topical medication. This difference was strongly correlated with ACD (P=0.003) in addition to IOP and CCT. In eyes treated with filtration surgery, ACD (P=0.04) again impacted the trends between nonglaucoma and glaucoma eyes. Conclusions Medication or filtration surgery did not affect the corneal biomechanical parameters differentially from nonglaucoma eyes. However, IOP, CCT, and ACD strongly affected corneal biomechanical parameters in the same glaucoma eyes.
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TL;DR: In this paper, the shape of the anterior surface of the peripapillary sclera (PPS) between glaucoma and healthy subjects was compared with spectral domain optical coherence tomography.
Abstract: Aims To compare the shape of the anterior surface of the peripapillary sclera (PPS) between glaucoma and healthy subjects. Methods 88 primary open angle glaucoma (POAG), 98 primary angle closure glaucoma (PACG) and 372 age-matched and gender-matched healthy controls were recruited in this study. The optic nerve head of one randomly selected eye of each subject was imaged with spectral domain optical coherence tomography. The shape of the PPS was measured through an angle defined between a line parallel to the nasal anterior PPS boundary and one parallel to the temporal side. A negative value indicated that the PPS followed an inverted v-shaped configuration (peak pointing towards the vitreous), whereas a positive value indicated that it followed a v-shaped configuration. Results The mean PPS angle in normal controls (4.56±5.99°) was significantly smaller than that in POAG (6.60±6.37°, p=0.011) and PACG (7.90±6.87°, p Conclusions The v-shaped configuration of the PPS was more pronounced in glaucoma eyes than in healthy eyes. This posterior bowing of the PPS may have an impact on the biomechanical environment of the optic nerve head.
8 citations
TL;DR: More myopic eyes had weaker biomechanical properties than the contralateral eye in anisometropic eyes, however, a certain linear relationship between an isometropia and biomechanicals asymmetry was not found.
Abstract: Purpose: To investigate the relationship between corneal biomechanical and ocular biometric parameters, and to explore biomechanical asymmetry between anisometropic eyes using the corneal visualization Scheimpflug technology device (Corvis ST). Methods: 180 anisometropic participants were included. Participants were divided into low (1.00≤△Spherical equivalent (SE) < 2.00D), moderate (2.00D≤△SE < 3.00D) and high (△SE ≥ 3.00D) anisometropic groups. Axial length (AL), keratometry, anterior chamber depth (ACD) and corneal biomechanical parameters were assessed using the OA-2000 biometer, Pentacam HR and Corvis ST, respectively. Results: The mean age of participants was 16.09 ± 5.64 years. Stress-Strain Index (SSI) was positively correlated with SE (r = 0.501, p < 0.001) and negatively correlated with AL (r = -0.436, p < 0.001). Some other Corvis ST parameters had weak correlation with SE or AL. Corneal biomechanical parameters except for time of first applanation (A1T), length of second applanation (A2L), deformation amplitude (DA), first applanation stiffness parameter (SPA1) and ambrosia relational thickness-horizontal (ARTh) were correlated with ametropic parameters (SE or AL) in multiple regression analyses. A1T, velocity of first applanation (A1V), time of second applanation (A2T), A2L, velocity of second applanation (A2V), corneal curvature radius at highest concavity (HCR), peak distance (PD), DA, deformation amplitude ratio max (2 mm) (DAR), SPA1, integrated radius (IR), and SSI showed significant differences between fellow eyes (p < 0.05). There was no significant difference in asymmetry of corneal biomechanics among the three groups (p > 0.05). Asymmetry of some biomechanical parameters had weak correlation with asymmetry of mean corneal curvatures and ACD. However, asymmetry of corneal biomechanical parameters was not correlated with asymmetry of SE or AL (p > 0.05). Conclusion: More myopic eyes had weaker biomechanical properties than the contralateral eye in anisometropia. However, a certain linear relationship between anisometropia and biomechanical asymmetry was not found.
1 citations
01 Jan 2021
TL;DR: In this paper, the authors review the available evidence on biomechanical implications of the use of drugs on the ocular tissues with emphasis on ocular rigidity, and highlight pathophysiologic pathways to side effects.
Abstract: Do certain drugs have the ability to influence ocular rigidity and biomechanics of the eye? This is an important question since it may elucidate mechanisms on how the drugs work or highlight pathophysiologic pathways to side effects. In addition, especially in intraocular pressure measurement, it may signify an increased probability of error in tonometry. In this chapter, we review the available evidence on biomechanical implications of the use of drugs on the ocular tissues with emphasis on ocular rigidity.
References
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TL;DR: This review describes a scheme for diagnosis of glaucoma in population based prevalence surveys that makes provision for diagnosing glauca in eyes with severe visual loss where formal field testing is impractical, and for blind eyes in which the optic disc cannot be seen because of media opacities.
Abstract: This review describes a scheme for diagnosis of glaucoma in population based prevalence surveys. Cases are diagnosed on the grounds of both structural and functional evidence of glaucomatous optic neuropathy. The scheme also makes provision for diagnosing glaucoma in eyes with severe visual loss where formal field testing is impractical, and for blind eyes in which the optic disc cannot be seen because of media opacities.
2,004 citations
TL;DR: In this paper, a cornea biomechanical model was used to understand and quantify intraocular pressure (IOP) measurement errors introduced by corneal variables during applanation tonometry, and the effect of each variable on the accuracy of IOP tonometry readings was examined quantitatively.
Abstract: Purpose To understand and quantify intraocular pressure (IOP) measurement errors introduced by corneal variables during applanation tonometry using a cornea biomechanical model. Setting Department of Ophthalmology, Biomedical Engineering Center, The Ohio State University, Columbus, Ohio, USA. Methods The model assumed an overall resultant pressure that was based on the summation of the applanation pressure, the true IOP, and the surface tension caused by the tear film to determine the final deformation of the corneal apex during IOP measurement. Corneal resistance was varied according to the cornea's biomechanical properties, thickness, and curvature, and the effect of each variable on the accuracy of IOP tonometry readings was examined quantitatively. Results The model demonstrated that tonometry readings do not always reflect true IOP values. They deviate when corneal thickness, curvature, or biomechanical properties vary from normal values. Based on the model, predicted IOP readings have a 2.87 mm Hg range resulting from the variation in the corneal thickness in the normal population and a 1.76 mm Hg range from the variation in the corneal radius of curvature. Considering that Young's modulus of the corneal varies from 0.1 to 0.9 MPa in the normal population, the model predicts tonometry IOP readings will have a range of 17.26 mm Hg because of the variation in this corneal biomechanical parameter alone. Conclusions The simulation based on the model demonstrated quantitatively that variations in each corneal variable cause errors in tonometry IOP readings. The simulation results indicate that differences in corneal biomechanics across individuals may have greater impact on IOP measurement errors than corneal thickness or curvature.
694 citations
TL;DR: The Bascom Palmer (Hodapp-Anderson-Parrish) GSS allows accurate staging of 100% of glaucoma on the basis of visual fields and other data, enabling evaluation of disease progression and resource utilization at various glauca stages.
421 citations
TL;DR: The random forest method with leave-one-out cross-validation (RF/LOOCV) provided the best artificial intelligence model for detecting ectasia and the TBI was sensitive for detecting subclinical ectasia among eyes with normal topography in very asymmetric patients.
Abstract: PURPOSE To present the Tomographic and Biomechanical Index (TBI), which combines Scheimpflugbased corneal tomography and biomechanics for enhancing ectasia detection. METHODS Patients from different continents were retrospectively studied. The normal group included 1 eye randomly selected from 480 patients with normal corneas and the keratoconus group included 1 eye randomly selected from 204 patients with keratoconus. There were two groups: 72 ectatic eyes with no surgery from 94 patients with very asymmetric ectasia (VAE-E group) and the fellow eyes of these patients with normal topography (VAE-NT group). Pentacam HR and Corvis ST (Oculus Optikgerate GmbH, Wetzlar, Germany) parameters were analyzed and combined using different artificial intelligence methods. The accuracies for detecting ectasia of the Belin/Ambrosio Deviation (BAD-D) and Corvis Biomechanical Index (CBI) were compared to the TBI, considering the areas under receiver operating characteristic curves (AUROCs). RESULTS The random forest method with leave-one-out cross-validation (RF/LOOCV) provided the best artificial intelligence model. The AUROC for detecting ectasia (keratoconus, VAE-E, and VAE-NT groups) of the TBI was 0.996, which was statistically higher (DeLong et al., P < .001) than the BAD-D (0.956) and CBI (0.936). The TBI cut-off value of 0.79 provided 100% sensitivity for detecting clinical ectasia (keratoconus and VAE-E groups) with 100% specificity. The AUROCs for the TBI, BAD-D, and CBI were 0.985, 0.839, and 0.822 in the VAE-NT group (DeLong et al., P < .001). An optimized TBI cut-off value of 0.29 provided 90.4% sensitivity with 96% specificity in the VAE-NT group. CONCLUSIONS The TBI generated by the RF/LOOCV provided greater accuracy for detecting ectasia than other techniques. The TBI was sensitive for detecting subclinical (fruste) ectasia among eyes with normal topography in very asymmetric patients. The TBI may also confirm unilateral ectasia, potentially characterizing the inherent ectasia susceptibility of the cornea, which should be the subject of future studies. [J Refract Surg. 2017;33(7):434-443.].
259 citations
TL;DR: Noncontact Brillouin microscopy allowed imaging and quantifying CXL-induced mechanical changes without contact in a depth-dependent manner at high spatial resolution, indicating that anterior stromal stiffening contributes the most to mechanical outcome.
Abstract: PURPOSE. Corneal collagen crosslinking (CXL) is designed to halt the progression of keratoconus and corneal ectasia by inducing corneal stiffening. However, it currently is difficult to monitor and evaluate CXL outcome objectively due to the lack of suitable methods to characterize corneal mechanical properties. We validated noncontact Brillouin microscopy to quantify corneal mechanical properties before and after CXL. METHODS. CXL was performed on fresh porcine eyes using various presoaking times and light doses, with or without epithelial debridement. From Brillouin maps of corneal elastic modulus, stiffness and average modulus of anterior, middle, and posterior stroma were analyzed. Corneal stiffening index (CSI) was introduced as a metric to compare the mechanical efficacy of a given CXL protocol with respect to the standard protocol (30-minute riboflavin presoak, 3 mW/cm 2 ultraviolet illumination for 30 minutes). RESULTS. Brillouin corneal stiffness increased significantly (P 0.98). Compared to the standard epioff procedure, a typical epi-on procedure resulted in a third of stiffness increase in porcine corneas (CSI ¼ 33).
213 citations