Characterization of Ocular Tissues Using Microindentation and Hertzian Viscoelastic Models

IOP is an important risk factor for glaucoma, and lowering IOP, even when IOP is within the normal range as defined epidemiologically, remains the only proven-effective treatment of the disease.However, our knowledge of the true nature of IOP in humans or how it affects ocular tissues is partially limited by the lack of continuous IOP monitoring technology for patients.Although clinical IOP reduction remains the only proven method for preventing the occurrence and progression of glaucoma, the role of IOP in the development and progression of the disease is not well understood.This is largely due to clinical observation that a significant number of patients with normal IOP develop glaucoma, while other individuals with elevated IOP show no signs of disease.This may mean that IOP (or some IOP-driven factor) is the primary triggering factor in glaucoma, and IOP vulnerability varies among individuals.Another possibility is that the clinical characterization of the secondary IOP using rare imaging measurements fails to capture the exposure to harmful IOP fluctuations that partially drive the disease in these normotensive patients with glaucoma, which contributes to the IOP-gloomy relationship.Recent data suggest that the IOP varies around 5 mmHg daily and hourly, and from 15 to 40 mmHg per second when measured continuously in awake patients.Very little is known about IOP fluctuations in humans and how The eye responds to these fluctuations, but IOP levels at all time points have the potential to cause disturbances in the neuroretic layer.Intraocular pressure assessment (IOP) is a key phase of routine eye examination, especially for patients with glaucoma. Indeed, in these cases, elevated IOP is the only risk factor that physicians can modify.This is why the IOP value is important to the patient: it is a key element in the diagnosis and management of glaucoma.The IOP depends on the speed of movement and the rate of leakage of the guiding light, ie it depends on the flow resistance ofн the drainage channels and the amount of episcleral venous pressure.Glaucoma is a slowly progressive neuropathy with changes in the optic nerve, retinalneurofibrillary layer (RNFL) and visual field.

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Computerized ultrasonic characterization of ocular tissues

The Journal of the Acoustical Society of America ◽

10.1121/1.2017288 ◽

1979 ◽

Vol 65 (S1) ◽

pp. S4-S4

Author(s):

F. L. Lizzi ◽

E. Feleppa ◽

J. Herbst ◽

N. Jaremko ◽

D. J. Coleman

Keyword(s):

Ocular Tissues ◽

Ultrasonic Characterization

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3D Characterization of corneal deformation using ultrasound speckle tracking

Journal of Innovative Optical Health Sciences ◽

10.1142/s1793545817420056 ◽

2017 ◽

Vol 10 (06) ◽

pp. 1742005 ◽

Cited By ~ 8

Author(s):

Keyton Clayson ◽

Elias Pavlatos ◽

Yanhui Ma ◽

Jun Liu

Keyword(s):

Speckle Tracking ◽

Mechanical Response ◽

Three Dimensional ◽

Average Volume ◽

Ocular Tissues ◽

Corneal Deformation ◽

Thin Spherical Shell ◽

Iop Elevation ◽

Dextran Solution

The three-dimensional (3D) mechanical response of the cornea to intraocular pressure (IOP) elevation has not been previously reported. In this study, we use an ultrasound speckle tracking technique to measure the 3D displacements and strains within the central 5.5[Formula: see text]mm of porcine corneas during the whole globe inflation. Inflation tests were performed on dextran-treated corneas (treated with a 10% dextran solution) and untreated corneas. The dextran-treated corneas showed an inflation response expected of a thin spherical shell, with through-thickness thinning and in-plane stretch, although the strain magnitudes exhibited a heterogeneous spatial distribution from the central to more peripheral cornea. The untreated eyes demonstrated a response consistent with swelling during experimentation, with through-thickness expansion overriding the inflation response. The average volume ratios obtained in both groups was near 1 confirming general incompressibility, but local regions of volume loss or expansion were observed. These results suggest that biomechanical measurements in 3D provide important new insight to understand the mechanical response of ocular tissues such as the cornea.

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Characterization of Mitochondrial GSH Transporters and Their Role in RPE Protection

10.20944/preprints201807.0346.v1 ◽

2018 ◽

Author(s):

Mo Wang ◽

Ling-ing Lau ◽

Parameswaran G. Sreekumar ◽

Christine Spee ◽

Lin Liu ◽

...

Keyword(s):

Oxidative Stress ◽

Retinal Pigment ◽

Retinal Pigment Epithelial Cells ◽

Age Related Macular Degeneration ◽

Ocular Tissues ◽

Age Related ◽

And Function ◽

And Oxidative Stress ◽

Pigment Epithelial Cells

Mitochondrial dysfunction and oxidative stress are thought to be relevant to the pathogenesis of age-related macular degeneration (AMD). Glutathione (GSH) homeostasis fulfills a number of important roles in mitochondria, such as maintenance of mitochondrial DNA and respiratory competency of cells. Although the transport of mitochondrial GSH (mGSH) is not fully understood, increasing evidence from non-ocular tissues suggests that OGC (2-oxoglutarate carrier, SLC25A11) and DIC (dicarboxylate carrier, SLC25A10) are involved in mGSH transport. However, whether OGC and DIC mediate the transfer of GSH into the mitochondria of retinal pigment epithelial cells (RPE) remains unknown. Thus, we investigated the expression, localization, and function of OGC and DIC in human RPE (hRPE) in relation to oxidative stress and GSH. Both OGC and DIC are expressed in hRPE and are localized in mitochondria. We also found a dose and time-dependent decrease of OGC and DIC expression under oxidative stress and increased expression in polarized RPE. Our data show that the downregulation of OGC and DIC resulted in increased apoptosis and mGSH depletion which can be overcome by co-treatment with GSH-MEE. These findings suggest that overexpression of OGC and DIC may be an effective strategy to decrease susceptibility to mitochondrial toxicants by elevation of mGSH.

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Multifocal choroiditis and choroidal tuberculoma: Signs of presumed ocular tuberculosis

European Journal of Ophthalmology ◽

10.1177/11206721211039938 ◽

2021 ◽

pp. 112067212110399

Author(s):

Marta Belmonte Grau ◽

Muxima Acebes García ◽

Juan Jacobo González Guijarro

Keyword(s):

Ocular Tissues ◽

Swept Source ◽

Radiographic Findings ◽

Ocular Tuberculosis ◽

Multifocal Choroiditis ◽

Oral Steroids ◽

Presumed Ocular Tuberculosis ◽

Choroidal Tuberculoma

The diagnosis of OTB (Ocular tuberculosis) is usually difficult to make. Definitive diagnosis requires the identification of M. tuberculosis organisms in ocular tissues or fluids, but samples are often difficult to obtain, and biopsy may be hard to justify. We describe a 50-years-old Maghreb male, who presented a multifocal choroiditis associated with a choroidal tuberculoma on the left eye. Based on positive QuantiFERON-TB-Gold test and suggestive clinical and radiographic findings, a diagnosis of presumed ocular tuberculosis was made. Serial swept-source optical coherence tomography (SS-OCT) and widefield fundus retinographies during subsequent follow-up visits demonstrated the characterization of the atypical tuberculosis presentation and allowed the assessment of response to antitubercular therapy and oral steroids.

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Linear and Quasi-Linear Viscoelastic Characterization of Ankle Ligaments

Journal of Biomechanical Engineering ◽

10.1115/1.429623 ◽

1999 ◽

Vol 122 (1) ◽

pp. 15-22 ◽

Cited By ~ 147

Author(s):

J. R. Funk ◽

G. W. Hall ◽

J. R. Crandall ◽

W. D. Pilkey

Keyword(s):

Lower Extremity ◽

Ankle Ligaments ◽

Viscoelastic Models ◽

Nonlinear Viscoelastic ◽

Human Ankle ◽

Linear Viscoelastic ◽

Failure Properties ◽

Linear And Nonlinear ◽

Model Failure

The objective of this study was to produce linear and nonlinear viscoelastic models of eight major ligaments in the human ankle/foot complex for use in computer models of the lower extremity. The ligaments included in this study were the anterior talofibular (ATaF), anterior tibiofibular (ATiF), anterior tibiotalar (ATT), calcaneofibular (CF), posterior talofibular (PTaF), posterior tibiofibular (PTiF), posterior tibiotalar (PTT), and tibiocalcaneal (TiC) ligaments. Step relaxation and ramp tests were performed. Back-extrapolation was used to correct for vibration effects and the error introduced by the finite rise time in step relaxation tests. Ligament behavior was found to be nonlinear viscoelastic, but could be adequately modeled up to 15 percent strain using Fung’s quasilinear viscoelastic (QLV) model. Failure properties and the effects of preconditioning were also examined. [S0148-0731(00)01001-3]

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