Optical coherence tomography measurements of the fresh porcine eye and response of the outer coats of the eye to volume increase (original) (raw)
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British Journal of Ophthalmology, 2007
Aim: To measure corneal and scleral radii of curvature in response to intraocular pressure (IOP). Methods: Using digital photographic profile images of 16 fresh porcine eyes, the curvatures of the cornea and sclera were determined in response to five consecutive incremental 100 ml saline intravitreal injections. IOP was measured and ocular rigidity calculated. Elastic moduli of the cornea and sclera were estimated. Results: Intraocular pressure and the radius of curvature of the sclera increased linearly with increasing volume. There was no statistical change in corneal curvature. The elasticity of the cornea and sclera was constant during the 15-50 mm Hg increase in IOP. The estimated range of the elastic moduli of the cornea and sclera were, respectively 0.07-0.29 MPa and 0.2 MPa to 0.5 MPa. The scleral rigidity ranged from 0.0017 to 0.0022. Conclusions: The elastic moduli of the cornea and sclera are independent of IOP. The modulus of elasticity of the sclera is higher than that of the cornea. Elevation of IOP changes the curvature of the sclera but not that of the cornea. Porcine scleral rigidity is similar to human scleral rigidity. Scleral curvature could be a novel method for measuring IOP.
The parameters of the porcine eyeball
Graefes Archive for Clinical and Experimental Ophthalmology, 2011
Background The eye of the domestic pig (Sus scrofa domestica) is an ex vivo animal model often used in vision sciences research (retina studies, glaucoma, cataracts, etc.). However, only a few papers have compiled pig eye anatomical descriptions. The purpose of this paper is to describe pig and human eye anatomical parameters to help investigators in their choice of animal model depending on their study objective. Methods A wide search of current medical literature was performed (English language) using PubMed. Anteroposterior axial length and corneal radius, astigmatism, vertical and horizontal diameter, and pachymetry (slit-scan and ultrasound) were measured in five enucleated pig eyes of animals 6 to 8 months old. Results Horizontal corneal diameter was 14.31 ± 0.25 mm (CI 95% 14.03 mm–14.59 mm), vertical diameter was 12.00 ± 0 mm, anteroposterior length was 23.9 ± 0.08 mm (CI 95% 23.01 mm–29.99 mm), central corneal ultrasound pachymetry was 877.6 ± 13.58 μm (CI 95% 865.70 μm–889.50 μm) and slit-scan pachymetry was 906.2 ± 15.30 μm (CI 95% 892.78 μm–919.61 μm). Automatic keratometry (main meridians) was 41.19 ± 1.76D and 38.83 ± 2.89D (CI 95% 40.53D–41.81D and 37.76D–39.89D respectively) with an astigmatism of 2.36 ± 1.70D (CI 95% 1.72D–3.00D), and manual keratometry was 41.05 ± 0.54D and 39.30 ± 1.15D (CI 95% 40.57D–41.52D and 38.29D–40.31D respectively) with an astigmatism of 1.75 ± 1.31D (CI 95% 0.60D–2.90D). Conclusion This paper describes the anatomy of the pig eyeball for easy use and interpretation by researchers who are considering their choice of animal model in vision sciences research.
Journal of Advances in VetBio Science and Techniques, 2022
The aim of this study was to determine intraocular pressure (IOP) and central corneal thickness (CCT) measurements in healthy rabbits to establish clinical reference values and to investigate the possible relationship between these measurements. The study included 40 eyes of 20 New Zealand albino rabbits, aged 1.5-2 years. All the eyes were healthy with no abnormalities, corneal disease, or evidence of glaucoma. An ultrasonographic pachymeter was used to measure CCT and TonoVet® was used to measure IOP. Correlations between IOP and CCT measurements were examined. The mean CCT was 388.2 ± 38.22 µm in the right eye and 391.8± 59.18 µm in the left eye. IOP was measured as 16 ± 3.76 mmHg in the right eye and 16 ± 2.73 mmHg in the left eye. No correlation was determined between the IOP and CCT, and this indicated that the TonoVet® readings of CCT and IOP did not cause a deviation that could be determined. There is a need for further studies of different animals to investigate the effect ...
American journal of veterinary research, 2017
OBJECTIVE To determine corneal thickness of eyes of healthy goats, sheep, and alpacas by use of a portable spectral-domain optical coherence tomography (SD-OCT) device and evaluate intraoperator reliability for measurements. ANIMALS 11 female goats, 10 female sheep, and 11 (4 males and 7 females) alpacas. PROCEDURES Each animal was sedated, and gentle manual restraint was used to ensure proper positioning of the head and globe. Corneal pachymetry was performed (in triplicate) with a portable SD-OCT device on both eyes of each animal. All corneal measurements were obtained manually by use of the integrated caliper function. Corneal epithelial thickness (CET), corneal stromal thickness (CST), Descemet membrane thickness (DMT), and total corneal thickness (TCT) were measured twice on each image, and a mean value was calculated. RESULTS Mean ± SD values for CET, CST, DMT, and TCT were 96.1 ± 5.0 μm, 486.0 ± 10.3 μm, 36.8 ± 4.8 μm, and 616.9 ± 7.1 μm, respectively, for the goats; 111.6 ±...
Translational Vision Science & Technology, 2021
To ascertain the influence of intraocular pressure (IOP) on corneal optical coherence tomography (OCT) speckle in untreated and ultraviolet A-riboflavin induced corneal collagen crosslinked rabbit eyes. Methods: Left corneas of eight rabbits were de-epithelialized and crosslinked by applying riboflavin and 30-minute ultraviolet A light exposure. After enucleation (6 months after treatment), each eyeball (treated and untreated) was mounted in a measurement setup, in which IOP was increased from 15 to 45 mm Hg in steps of 5 mm Hg. At each IOP value, single B-scans of the central cornea were acquired three times with the spectral-domain OCT Copernicus-HR. Then, three regions of interest, including the anterior, posterior, and entire corneal stroma, were automatically extracted. Five different probability distributions were used as a model for the corneal speckle and the one with the best goodness of fit was chosen for further analysis. Results: The generalized gamma distribution achieved the best goodness of fit and its scale (a) and shape (v) parameters statistically significantly changed with increasing IOP in the three regions of analysis (two-way repeated measures analysis of variance, all P < 0.05). The statistically significant difference between untreated and crosslinked eyes was observed for the shape parameters of the posterior and entire corneal stroma. Conclusions: Corneal OCT speckle is influenced by IOP and shows to be significantly different in untreated and crosslinked eyes. Corneal OCT speckle analysis has the potential to be indirectly used for assessing changes in corneal stroma in ex vivo and in vivo studies. Translational Relevance: Investigation of corneal OCT speckle statistics can offer additional diagnostic biomarkers related to changes in the corneal stroma after ocular surgeries.
The Impact of Acutely Elevated Intraocular Pressure on the Porcine Optic Nerve Head
Investigative Opthalmology & Visual Science, 2011
PURPOSE. To investigate the effects of acute elevations in intraocular pressure (IOP) on the cup, prelaminar, and lamina cribrosa regions of the porcine optic nerve head (ONH). METHODS. Ex vivo imaging of 10 porcine ONHs was performed using spectral-domain optical coherence tomography (OCT). The IOP was manipulated with a pressure head and measured with a pressure transducer. Reference scans were taken at 0 mm Hg, before further scanning was performed at 7-mm Hg steps, up to 49 mm Hg. Morphometric parameters were measured across centrally located OCT B-scans at different IOPs, and the relationship between IOP and changes in these parameters was analyzed. RESULTS. As IOP increased from 0 to 49 mm Hg, mean crosssectional cup area increased (28% Ϯ 3%, P Ͻ 0.001), lamina cribrosa area decreased (18% Ϯ 2%, P Ͻ 0.001), and prelaminar tissue area decreased (5.5% Ϯ 0.5%, P Ͻ 0.001). Multivariate regression demonstrated that most of the change in cup area is associated with changes in both lamina cribrosa position and thickness (r ϭ 0.89, P Ͻ 0.001). CONCLUSIONS. Acute elevations in IOP were shown to result in posterior displacement of ONH, as well as lamina cribrosa and prelaminar tissue deformation in the porcine ONH.
Determination of the true intraocular pressure and modulus of elasticity of the human cornea in vivo
Bulletin of mathematical biology, 1999
The purpose of this study was to determine the true intraocular pressure and modulus of elasticity of the human cornea in vivo. The cornea was modeled as a shell, and the equations for the deformations of a shell due to applanating and intraocular pressures were combined to model the behavior of the cornea during applanation tonometry. At certain corneal dimensions called the calibration dimensions, the applanating and intraocular pressures are considered to be equal. This relationship was used to determine the modulus of elasticity of the cornea and the relationship between the applanating and intraocular pressures. The true intraocular pressure (IOPT) was found to be related to Goldmann's applanating pressure (IOPG) as IOPT = IOPG/K , where K is a correction factor. For the calibration corneal thickness of 0.52 mm, the modulus of elasticity E in MPa of the human cornea was found to be related to the true intraocular pressure IOPT in mmHg as E = 0.0229IOPT. The generalization of the Imbert-Fick law that takes into account the effect of corneal dimensions and stiffness was found to be given by IOPT = 73.5W/(K A), where W is the applanating weight in gf (gram force) and A is the applanated area in mm 2. The calculated true intraocular pressure and modulus of elasticity were found to agree with published experimental results. The mathematical model developed may therefore be used to improve results from applanation tonometry and to estimate the mechanical property of the cornea in vivo.
Investigative Ophthalmology & Visual Science, 2011
PURPOSE. To determine whether acutely elevated IOP alters optic nerve head (ONH) structural parameters characterized in vivo using spectral domain optical coherence tomography (SD-OCT). METHODS. Five rhesus macaques were tested under isoflurane anesthesia. SD-OCT images of the ONH of both eyes were acquired 30 minutes after IOP was stabilized to 10 mm Hg and 60 minutes after stabilization to 45 mm Hg. The internal limiting membrane, Bruch's membrane/retinal pigment epithelium, neural canal opening (NCO), and anterior lamina cribrosa surface (ALCS) were delineated using custom software. Differences in SD-OCT structural parameters between the two IOP levels were assessed using generalized estimating equations. In six eyes of three animals, images were acquired after 10 minutes and 30 minutes of IOP stabilization to 10 mm Hg (control experiment). RESULTS. Acute IOP elevation resulted in a reduction in prelaminar tissue thickness (mean, Ϫ47 m; SD, 25 m; P ϭ 0.002), rim volume (Ϫ0.05 mm 3 , 0.02 mm 3 ; P ϭ 0.002), rim width (Ϫ30 m, 7 m; P ϭ 0.002), and in an increase in NCO depth (38 m, 15 m; P ϭ 0.002). An increase in ALCS depth was significant relative to peripheral Bruch's membrane (48 m, 24 m; P ϭ 0.002) but not relative to the NCO. No significant parameter changes were detected in the control eyes. CONCLUSIONS. Surface compliance changes in the normal monkey ONH primarily reflect prelaminar and peripapillary deformation. SD-OCT compliance testing will further our understanding of the effects of IOP on the ONH and help improve and validate numerical models of ONH biomechanics.
The effect of intraocular pressure on chick eye geometry and its application to myopia
Acta of bioengineering and biomechanics / Wroclaw University of Technology
Myopia is characterized by an increase in axial length of the eye, but the reasons for the axial elongation are still unknown. Higher intraocular pressure (IOP) has been associated with myopia and could be involved in eye enlargement. The purpose of this study was to investigate the effect of intraocular pressure on the geometry of the chick eye and to investigate whether an increase in IOP could cause the elongation of the eye. The IOP of ten 7-day old chick eyes was raised by injecting fluid into the eyes and the resulting deformation of the eyes was measured using digital cameras. In-vitro pressure-volume curves were obtained. The axial and equatorial strains (deformation normalized to the original dimension) were calculated. Our results showed that IOP increased exponentially with increasing injected volume. About 25 D myopia could be induced by the axial elongation created with an increase in IOP by 100 mmHg. As pressure increased from 0 to 140 mmHg, the chick eye elongated in ...