Intraocular pressure and three-dimensional corneal biomechanics

There is a general consensus that elevation in intraocular pressure (IOP), due to a reduced outflow of aqueous humor, is a major factor leading to primary open-angle glaucoma (POAG). Studies indicated that the damage of the optic nervehead (ONH), due to the biomechanical environment in and around the lamina cribrosa (LC), could be an important event leading to POAG [Morgan]. Since experimentally testing tissues of such small dimensions is difficult, many researchers resorted to computationally model the biomechincal environment inside the eye [Avatar, Kobayashi, Sigal, Uchio, Xu, Tandon]. It also gives the flexibility to parametrically study and isolate the effects of individual tissues on the IOP and LC. Many of these studies involve stress analysis on a hypothetical geometry (for e.g. spherical or axisymmetric hemisphere) using a variety of constitutive models (for e.g. elastic, biphasic etc) to study the static, and dynamic response of the IOP [Tandon, Sigal].

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Corneal biomechanics and intraocular pressure assessment after penetrating keratoplasty for non keratoconic patients, long term results

BMC Ophthalmology ◽

10.1186/s12886-019-1186-y ◽

2019 ◽

Vol 19 (1) ◽

Cited By ~ 2

Author(s):

Mohamed Samy Abd Elaziz ◽

Hoda Mohamed Elsobky ◽

Adel Galal Zaky ◽

Eslam Ahmed Maher Hassan ◽

Mahmoud Tawfik KhalafAllah

Keyword(s):

Intraocular Pressure ◽

Penetrating Keratoplasty ◽

Corneal Biomechanics ◽

Long Term Results

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Probing biomechanical properties of the cornea with air-puff-based techniques – an overview

Advanced Optical Technologies ◽

10.1515/aot-2021-0042 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Patryk Mlyniuk ◽

Ewa Maczynska-Walkowiak ◽

Jagoda Rzeszewska-Zamiara ◽

Ireneusz Grulkowski ◽

Bartlomiej J. Kaluzny

Keyword(s):

Intraocular Pressure ◽

Mechanical Load ◽

Accurate Determination ◽

Anterior Segment ◽

External Environment ◽

Standard Technique ◽

Biomechanical Properties ◽

Corneal Biomechanics ◽

Optical Methods ◽

Optical Coherence

Abstract The cornea is a part of the anterior segment of the eye that plays an essential optical role in refracting the light rays on the retina. Cornea also preserves the shape of an eyeball and constitutes a mechanical barrier, protecting the eye against the factors of the external environment. The structure of the cornea influences its biomechanical properties and ensures appropriate mechanical load transfer (that depends on the external environment and the intraocular pressure) while maintaining its shape (to a certain extent) and its transparency. The assessment of the corneal biomechanics is important in clinical ophthalmology, e.g. in the diagnosis of ectatic corneal diseases, for precise planning of the refractive surgery, and in accurate determination of the intraocular pressure. A standard technique to determine corneal biomechanics requires the application of well-defined mechanical stimulus (e.g. air puff) and performing simultaneous imaging of the response of the tissue to the stimulus. A number of methods to assess the biomechanical properties of the cornea have been developed, including ultrasound, magnetic resonance imaging, and optical methods as visualization modalities. Commercially available methods include the ocular response analyzer (ORA) and corneal visualization scheimpflug technology (Corvis ST). Currently advanced research is conducted using optical coherence tomography (OCT). The extension of OCT called optical coherence elastography (OCE) possesses high clinical potential due to the imaging speed, noncontact character, and high resolution of images.

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Intraocular pressure changes and corneal biomechanics after hyperopic small-incision lenticule extraction

10.21203/rs.2.18089/v1 ◽

2019 ◽

Author(s):

Dan Fu ◽

Meiyan Li ◽

Michael C. Knorz ◽

Shengsheng Wei ◽

Jianmin Shang ◽

...

Keyword(s):

Intraocular Pressure ◽

Mixed Model ◽

Linear Mixed Model ◽

Corneal Thickness ◽

Corneal Biomechanics ◽

Ocular Response Analyzer ◽

Small Incision Lenticule Extraction ◽

Corvis St ◽

Small Incision ◽

Lenticule Extraction

Abstract Background: To compare intraocular pressure (IOP) measurements by a dynamic Scheimpflug analyzer (Corvis ST), a non-contact tonometer, and the ocular response analyzer following hyperopic small-incision lenticule extraction (SMILE).Methods: Thirteen patients underwent hyperopic SMILE in one eye each were prospectively enrolled. IOP and corneal biomechanical parameters were measured preoperatively and 1 week, 1 month, and 3 months after surgery with a non-contact tonometer (IOPNCT), Corvis ST (biomechanical corrected IOP, bIOP), and the ocular response analyzer (Goldmann-correlated intraocular pressure [IOPg], cornea compensated IOP [IOPcc]). A linear mixed model was used to compare IOP and biomechanical values among the methods at each time point.Results: IOPNCT, IOPg, and IOPcc dropped significantly after surgery, with the amplitude being 3.15±0.48 mmHg, 5.49±0.94 mmHg, and 4.34±0.97 mmHg, respectively, at the last visit. IOPNCT decreased by 0.11±0.06 mmHg per µm of removed central corneal thickness. bIOP did not change significantly after surgery. Before surgery, no difference was found among the measurements (P> 0.05). After surgery, IOPNCT and bIOP were higher than IOPg and IOPcc. bIOP is independent of cornea thickness at the last visit, while correlated significantly with corneal biomechanics as other three IOP values did.Conclusion: bIOP (biomechanical corrected IOP as measured with the Corvis ST) seems to be an accurate parameter to measure IOP after hyperopic SMILE.

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Biomechanical Evaluations of Ocular Injury Risk for Blast Loading

Journal of Biomechanical Engineering ◽

10.1115/1.4037072 ◽

2017 ◽

Vol 139 (8) ◽

Cited By ~ 5

Author(s):

Bahram Notghi ◽

Rajneesh Bhardwaj ◽

Shantanu Bailoor ◽

Kimberly A. Thompson ◽

Ashley A. Weaver ◽

...

Keyword(s):

Intraocular Pressure ◽

Injury Risk ◽

Animal Studies ◽

Experimental Studies ◽

Three Dimensional ◽

Blast Loading ◽

Ocular Injury ◽

Tissue Properties ◽

Primary Blast ◽

Combat Injuries

Ocular trauma is one of the most common types of combat injuries resulting from the exposure of military personnel with improvised explosive devices. The injury mechanism associated with the primary blast wave is poorly understood. We employed a three-dimensional computational model, which included the main internal ocular structures of the eye, spatially varying thickness of the cornea-scleral shell, and nonlinear tissue properties, to calculate the intraocular pressure and stress state of the eye wall and internal ocular structure caused by the blast. The intraocular pressure and stress magnitudes were applied to estimate the injury risk using existing models for blunt impact and blast loading. The simulation results demonstrated that blast loading can induce significant stresses in the different components of the eyes that correlate with observed primary blast injuries in animal studies. Different injury models produced widely different injury risk predictions, which highlights the need for experimental studies evaluating mechanical and functional damage to the ocular structures caused by the blast loading.

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