Dataset Information

Quantifying the effects of hydration on corneal stiffness with noncontact optical coherence elastography.

ABSTRACT: PURPOSE:To quantify the effects of the hydration state on the Young's modulus of the cornea. SETTING:Biomedical Optics Laboratory, University of Houston, Houston, Texas, USA. DESIGN:Experimental study. METHODS:Noncontact, dynamic optical coherence elastography (OCE) measurements were taken of in situ rabbit corneas in the whole eye-globe configuration (n = 10) and at an artificially controlled intraocular pressure of 15 mm Hg. Baseline OCE measurements were taken by topically hydrating the corneas with saline for 1 hour. The corneas were then dehydrated topically with a 20% dextran solution for another hour, and the OCE measurements were repeated. A finite element method was used to quantify the Young's modulus of the corneas based on the OCE measurements. RESULTS:The thickness of the corneas shrank considerably after topical addition of the 20% dextran solution (?680 ?m to ?370 ?m), and the OCE-measured elastic-wave speed correspondingly decreased (?3.2 m/s to ?2.6 m/s). The finite element method results showed an increase in Young's modulus (500 kPa to 800 kPa) resulting from dehydration and subsequent thinning. CONCLUSION:Young's modulus increased significantly as the corneas dehydrated and thinned, showing that corneal geometry and hydration state are critical factors for accurately quantifying corneal biomechanical properties.

SUBMITTER: Singh M

PROVIDER: S-EPMC6097919 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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Quantifying the effects of hydration on corneal stiffness with noncontact optical coherence elastography.

Singh Manmohan M Han Zhaolong Z Li Jiasong J Vantipalli Srilatha S Aglyamov Salavat R SR Twa Michael D MD Larin Kirill V KV

Journal of cataract and refractive surgery 20180723 8

<h4>Purpose</h4>To quantify the effects of the hydration state on the Young's modulus of the cornea.<h4>Setting</h4>Biomedical Optics Laboratory, University of Houston, Houston, Texas, USA.<h4>Design</h4>Experimental study.<h4>Methods</h4>Noncontact, dynamic optical coherence elastography (OCE) measurements were taken of in situ rabbit corneas in the whole eye-globe configuration (n = 10) and at an artificially controlled intraocular pressure of 15 mm Hg. Baseline OCE measurements were taken by ...[more]

PMID: 30049567

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Project description:SIGNIFICANCE:Measured corneal biomechanical properties are driven by intraocular pressure, tissue thickness, and inherent material properties. We demonstrate tissue thickness as an important factor in the measurement of corneal biomechanics that can confound short-term effects due to UV riboflavin cross-linking (CXL) treatment. PURPOSE:We isolate the effects of tissue thickness on the measured corneal biomechanical properties using optical coherence elastography by experimentally altering the tissue hydration state and stiffness. METHODS:Dynamic optical coherence elastography was performed using phase-sensitive optical coherence tomography imaging to quantify the tissue deformation dynamics resulting from a spatially discrete, low-force air pulse (150-?m spot size; 0.8-millisecond duration; <10 Pa [<0.08 mmHg]). The time-dependent surface deformation is characterized by a viscoelastic tissue recovery response, quantified by an exponential decay constant-relaxation rate. Ex vivo rabbit globes (n = 10) with fixed intraocular pressure (15 mmHg) were topically instilled every 5 minutes with 0.9% saline for 60 minutes and 20% dextran for another 60 minutes. Measurements were made after every 20 minutes to determine the central corneal thickness (CCT) and the relaxation rates. Cross-linking treatment was performed on another 13 eyes, applying isotonic riboflavin (n = 6) and hypertonic riboflavin (n = 7) every 5 minutes for 30 minutes, followed by UV irradiation (365 nm, 3 mW/cm) for 30 minutes while instilling riboflavin. Central corneal thickness and relaxation rates were obtained before and after CXL treatment. RESULTS:Corneal thickness was positively correlated (R = 0.9) with relaxation rates. In the CXL-treated eyes, isotonic riboflavin did not affect CCT and showed a significant increase in relaxation rates (+10%; P = .01) from 2.29 ms to 2.53 ms. Hypertonic riboflavin showed a significant CCT decrease (-31%; P = .01) from 618 ?m to 429 ?m but showed little change in relaxation rates after CXL treatment. CONCLUSIONS:Corneal thickness and stiffness are correlated positively. A higher relaxation rate implied stiffer material properties after isotonic CXL treatment. Hypertonic CXL treatment results in a stiffness decrease that offsets the stiffness increase with CXL treatment.

Project description:PurposeTo assess depth-dependent corneal displacements in live normal subjects using optical coherence elastography (OCE).MethodsA corneal elastography method based on swept-source optical coherence tomography (OCT) was implemented in a clinical prototype. Low amplitude corneal deformation was produced during OCT imaging with a linear actuator-driven lens coupled to force transducers. A cross-correlation algorithm was applied to track frame-by-frame speckle displacement across horizontal meridian scans. Intra-measurement force and displacement data series were plotted against each other to produce local axial stiffness approximations, k, defined by the slope of a linear fit to the force/displacement data (ignoring non-axial contributions from corneal bending). Elastographic maps displaying local k values across the cornea were generated, and the ratio of mean axial stiffness approximations for adjacent anterior and posterior stromal regions, ka/kp, was calculated. Intraclass correlation coefficients (ICC) were used to estimate repeatability.ResultsSeventeen eyes (ten subjects) were included in this prospective first-in-humans translational study. The ICC was 0.84. Graphs of force vs. displacement demonstrated that, for simultaneously acquired measurements involving the same applied force, anterior stromal displacements were lower (suggesting stiffer behavior) than posterior stromal displacements. Mean ka was 0.016±0.004 g/mm and mean kp was 0.014±0.004 g/mm, giving a mean ka/kp ratio of 1.123±0.062.ConclusionOCE is a clinically feasible, non-invasive corneal biomechanical characterization method capable of resolving depth-dependent differences in corneal deformation behavior. The anterior stroma demonstrated responses consistent with stiffer properties in compression than the posterior stroma, but to a degree that varied across normal eyes. The clinical capability to measure these differences has implications for assessing the biomechanical impact of corneal refractive surgeries and for ectasia risk screening applications.

Dataset Information

Quantifying the effects of hydration on corneal stiffness with noncontact optical coherence elastography.

Publications

Quantifying the effects of hydration on corneal stiffness with noncontact optical coherence elastography.

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