Detection of Corneal Ectasia Using OCT Maps of Pachymetry and Posterior Surface Mean Curvature.

Purpose: To quantify the abnormal corneal thinning and posterior surface steepening that is observed in keratoconus with an Ectasia Index.

Methods: Optical coherence tomography (OCT) was used to image the corneas of normal individuals and patients with varying stages of keratoconus (manifest, subclinical, and forme fruste). Maps of corneal pachymetry and posterior surface mean curvature were generated, and an Ectasia Index was calculated by multiplying Gaussian fits obtained from the two types of maps.

Measuring corneal astigmatism using OCT in keratoconus.

Purpose: To measure net corneal astigmatism using optical coherence tomography (OCT) (Avanti) in individuals with keratoconus and compare the repeatability and accuracy with those obtained using Scheimpflug imaging (Pentacam HR).

Setting: Casey Eye Institute, Portland, Oregon.

Design: Prospective cross-sectional observational study.

Differentiating Between Contact Lens Warpage and Keratoconus Using OCT Maps of Corneal Mean Curvature and Epithelial Thickness.

Purpose: To formulate an Epithelial Modulation index to differentiate between eyes with contact lens warpage and keratoconus.

Methods: Normal eyes and eyes with either contact lens warpage or keratoconus were scanned by a Fourier-domain optical coherence tomography (OCT) system. Maps of epithelial thickness and anterior surface mean curvature were generated and converted to deviation maps by subtracting the average maps from a healthy population.

Accuracy of OCT-derived net corneal astigmatism measurement.

Purpose: To assess the repeatability and accuracy of corneal astigmatism measurement with a spectral-domain optical coherence tomography (OCT) system (Avanti, Optovue) and compare them with Scheimpflug imaging (Pentacam HR, Oculus) and swept-source optical biometry (IOLMaster 700, Carl Zeiss Meditec AG).

Setting: Casey Eye Institute, Oregon Health & Science University, Portland, Oregon.

Design: Prospective cross-sectional observational study.

Eye motion correction algorithm for OCT-based corneal topography.

With its sequential image acquisition, OCT-based corneal topography is often susceptible to measurement errors due to eye motion. We have developed a novel algorithm to detect eye motion and minimize its impact on OCT topography maps. We applied the eye motion correction algorithm to corneal topographic scans acquired using a 70 kHz spectral-domain OCT device.

Keratoconus detection using OCT corneal and epithelial thickness map parameters and patterns.

Purpose: To detect keratoconus using optical coherence tomography (OCT) corneal map parameters and patterns.

Setting: Casey Eye Institute, Oregon Health and Science University, Portland, Oregon.

Design: Cross-sectional observational study.

A Coincident Thinning Index for Keratoconus Identification Using OCT Pachymetry and Epithelial Thickness Maps.

Purpose: To develop a coincident thinning (CTN) index to differentiate between keratoconic and healthy corneas using optical coherence tomography (OCT) measurements of pachymetry and epithelial thickness.

Methods: Pattern deviation maps of pachymetry and epithelial thickness were generated using Fourier-domain OCT images of the cornea. The co-localized thinning of the two maps was quantified using a novel CTN index, which was calculated from Gaussian fits of the regions of maximum relative thinning.

IOP-induced regional displacements in the optic nerve head and correlation with peripapillary sclera thickness.

Mechanical insult induced by intraocular pressure (IOP) is likely a driving force in the disease process of glaucoma. This study aimed to evaluate regional displacements in human optic nerve head (ONH) and peripapillary tissue (PPT) in response to acute IOP elevations, and their correlations with morphological characteristics of the posterior eye. Cross-sectional (2D) images of the ONH and PPT in 14 globes of 14 human donors were acquired with high-frequency ultrasound during whole globe inflation from 5 to 30 mm Hg.

Ocular Pulse Elastography: Imaging Corneal Biomechanical Responses to Simulated Ocular Pulse Using Ultrasound.

Purpose: In vivo evaluation of corneal biomechanics holds the potential for improving diagnosis and management of ocular diseases. We aimed to develop an ocular pulse elastography (OPE) technique to quantify corneal strains generated by naturally occurring pulsations of the intraocular pressure (IOP) using high-frequency ultrasound.

Methods: Simulated ocular pulses were induced in whole porcine and human donor globes to investigate the effects of physiologic variations in baseline IOP, ocular pulse amplitude, and frequency on corneal strains.

Three-Dimensional Inflation Response of Porcine Optic Nerve Head Using High-Frequency Ultrasound Elastography.

Characterization of the biomechanical behavior of the optic nerve head (ONH) in response to intraocular pressure (IOP) elevation is important for understanding glaucoma susceptibility. In this study, we aimed to develop and validate a three-dimensional (3D) ultrasound elastographic technique to obtain mapping and visualization of the 3D distributive displacements and strains of the ONH and surrounding peripapillary tissue (PPT) during whole globe inflation from 15 to 30 mmHg. 3D scans of the posterior eye around the ONH were acquired through full tissue thickness with a high-frequency ultrasound system (50 MHz).

Corneal Hydration Control during Ex Vivo Experimentation Using Poloxamers.

: The purpose of this study was to develop an effective treatment method using poloxamers to restore and maintain physiological hydration in postmortem porcine and human corneas during ex vivo experimentation, and to compare corneal inflation response with or without treatment.: Corneal buttons obtained from whole globes (n = 30 porcine, n = 8 human) were treated with various concentrations of poloxamer 188 (P188, a synthetic macromolecule surfactant) for 24 hrs to identify the concentration that would return the cornea to near-physiological hydration (i.e.

Mechanical Deformation of Human Optic Nerve Head and Peripapillary Tissue in Response to Acute IOP Elevation.

Purpose: To measure the deformation of the human optic nerve head (ONH) and peripapillary tissue (PPT) in response to acute intraocular pressure (IOP) elevation.

Methods: The ONH and PPT of 14 human donor globes were imaged with high-frequency ultrasonography during inflation testing from 5 to 30 mm Hg. A correlation-based speckle tracking algorithm was used to compute tissue displacements, and the through-thickness, in-plane, and shear strains were calculated by using least-squares strain estimation methods.

Regional Deformation of the Optic Nerve Head and Peripapillary Sclera During IOP Elevation.

Purpose: To measure the deformation of the porcine optic nerve head (ONH) and peripapillary sclera (PPS) in response to intraocular pressure (IOP) elevation.

Methods: High-frequency ultrasound was used to image the ONH and PPS of 12 porcine eyes during ex vivo inflation testing from 5 to 30 mm Hg. A speckle tracking algorithm was used to compute tissue displacements in the anterior-posterior direction and expansion of the scleral canal.

Imaging Corneal Biomechanical Responses to Ocular Pulse Using High-Frequency Ultrasound.

Imaging corneal biomechanical changes or abnormalities is important for better clinical diagnosis and treatment of corneal diseases. We propose a novel ultrasound-based method, called ocular pulse elastography (OPE), to image corneal deformation during the naturally occurring ocular pulse. Experiments on animal and human donor eyes, as well as synthetic radiofrequency (RF) data, were used to evaluate the efficacy of the OPE method.

3D Characterization of corneal deformation using ultrasound speckle tracking.

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 mm of porcine corneas during the whole globe inflation.

Corneoscleral stiffening increases IOP spike magnitudes during rapid microvolumetric change in the eye.

Factors governing the steady-state IOP have been extensively studied; however, the dynamic aspects of IOP are less understood. Clinical studies have suggested that intraocular pressure (IOP) fluctuation may be associated with glaucoma risk. This study aims to investigate how stiffening of corneoscleral biomechanical properties affects IOP spikes induced by rapid microvolumetric change.

Three-Dimensional Strains in Human Posterior Sclera Using Ultrasound Speckle Tracking.

Intraocular pressure (IOP) induced strains in the peripapillary sclera may play a role in glaucoma progression. Using inflation testing and ultrasound speckle tracking, the 3D strains in the peripapillary sclera were measured in nine human donor globes. Our results showed that the peripapillary sclera experienced through-thickness compression and meridional stretch during inflation, while minimal circumferential dilation was observed when IOP was increased from 10 to 19 mmHg.