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1.
J Vis ; 23(11): 38, 2023 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-37733540

RESUMO

Progression of myopia is usually accompanied by axial overgrowth of the eyeball, which affects scleral biomechanics (BM). To study scleral biomechanics, we propose the use of air-puff deformation swept-source OCT imaging. Air-puff deformation imaging was performed at different sites of ex vivo porcine (n=5) and rabbit (n=3) eyes, (<24hr postmortem): Nasal/temporal equatorial and posterior sclera (NE, NP, TE, TP), superior (S) and inferior (I) sclera, and cornea (C). Intraocular pressure was kept at 15mmHg. Deformation data were used as input to inverse finite element model (FEM) algorithms to reconstruct BM properties. Experimental deformation amplitudes showed dependence on the animal model, with porcine scleras exhibiting greater inter-site variation (displacement of S, I was up to four times greater than that of N, T), while rabbit scleras exhibited at most 40% of displacement differences between all sites. Both models showed significant (p<.001) differences in the temporal deformation profile between sclera and (C), but similarities in all scleral locations, suggesting that the scleral temporal profile is independent of scleral thickness variations. The FEM estimated an elastic modulus of 1.84 ± 0.30 MPa (I) to 6.04 ± 2.11 MPa (TE) for the porcine sclera. The use of scleral air-puff imaging is promising for noninvasive investigation of structural changes in the sclera associated with myopia and for monitoring possible modulation of scleral stiffness with myopia treatment.


Assuntos
Miopia , Tomografia de Coerência Óptica , Animais , Coelhos , Suínos , Esclera/diagnóstico por imagem , Algoritmos , Fenômenos Biomecânicos , Miopia/diagnóstico por imagem
2.
Opt Express ; 22(5): 5641-50, 2014 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-24663905

RESUMO

We report high sensitivity detection and tracking of a single fluorescent nanoparticle in solution by use of four alternately pulsed laser diodes for fluorescence excitation in a confocal microscope. Slight offsets between the centers of the overlapping laser foci together with time-resolved photon counting enable sub-micron precision position measurements. Real-time correction for diffusional motion with a xyz-piezo stage then enables tracking of a nanoparticle with diffusivity up to ~12 µm(2) s(-1). Fluorescence correlation spectroscopy and calibration measurements indicate a net fluorescence photon detection efficiency of ~6-9%, comparable to that of an optimized single-molecule microscope.

3.
Invest Ophthalmol Vis Sci ; 65(8): 8, 2024 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-38958968

RESUMO

Purpose: The purpose of this study was to evaluate the biomechanical and hydration differences in scleral tissue after two modalities of collagen cross-linking. Methods: Scleral tissue from 40 adult white rabbit eyes was crosslinked by application of 0.1% Rose Bengal solution followed by 80 J/cm2 green light irradiation (RGX) or by application of 0.1% riboflavin solution followed by 5.4 J/cm2 ultraviolet A irradiation (UVX). Posterior scleral strips were excised from treated and untreated sclera for tensile and hydration-tensile tests. For tensile tests, the strips were subjected to uniaxial extension after excision. For hydration-tensile tests, the strips were dehydrated, rehydrated, and then tested. Young's modulus at 8% strain and swelling rate were estimated. ANOVAs were used to test treated-induced differences in scleral biomechanical and hydration properties. Results: Photo-crosslinked sclera tissue was stiffer (Young's modulus at 8% strain: 10.7 ± 4.5 MPa, on average across treatments) than untreated scleral tissue (7.1 ± 4.0 MPa). Scleral stiffness increased 132% after RGX and 90% after UVX compared to untreated sclera. Scleral swelling rate was reduced by 11% after RGX and by 13% after UVX. The stiffness of the treated sclera was also associated with the tissue hydration level. The lower the swelling, the higher the Young's modulus of RGX (-3.8% swelling/MPa) and UVX (-3.5% swelling/MPa) treated sclera. Conclusions: Cross-linking with RGX and UVX impacted the stiffness and hydration of rabbit posterior sclera. The Rose Bengal with green light irradiation may be an alternative method to determine the efficacy and suitability of inducing scleral tissue stiffening in the treatment of myopia.


Assuntos
Reagentes de Ligações Cruzadas , Fármacos Fotossensibilizantes , Riboflavina , Rosa Bengala , Esclera , Raios Ultravioleta , Animais , Coelhos , Reagentes de Ligações Cruzadas/farmacologia , Fármacos Fotossensibilizantes/farmacologia , Riboflavina/farmacologia , Rosa Bengala/farmacologia , Resistência à Tração , Fenômenos Biomecânicos , Módulo de Elasticidade , Colágeno/metabolismo , Elasticidade
4.
Biomed Opt Express ; 12(10): 6341-6359, 2021 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-34745741

RESUMO

We introduce a method to estimate the biomechanical properties of the porcine sclera in intact eye globes ex vivo, using optical coherence tomography that is coupled with an air-puff excitation source, and inverse optimization techniques based on finite element modeling. Air-puff induced tissue deformation was determined at seven different locations on the ocular globe, and the maximum apex deformation, the deformation velocity, and the arc-length during deformation were quantified. In the sclera, the experimental maximum deformation amplitude and the corresponding arc length were dependent on the location of air-puff excitation. The normalized temporal deformation profile of the sclera was distinct from that in the cornea, but similar in all tested scleral locations, suggesting that this profile is independent of variations in scleral thickness. Inverse optimization techniques showed that the estimated scleral elastic modulus ranged from 1.84 ± 0.30 MPa (equatorial inferior) to 6.04 ± 2.11 MPa (equatorial temporal). The use of scleral air-puff imaging holds promise for non-invasively investigating the structural changes in the sclera associated with myopia and glaucoma, and for monitoring potential modulation of scleral stiffness in disease or treatment.

5.
Invest Ophthalmol Vis Sci ; 61(3): 28, 2020 03 09.
Artigo em Inglês | MEDLINE | ID: mdl-32186674

RESUMO

Purpose: Photoactivated cornea collagen cross-linking (CXL) increases corneal stiffness by initiating formation of covalent bonds between stromal proteins. Because CXL depends on diffusion to distribute the photoinitiator, a gradient of CXL efficiency with depth is expected that may affect the degree of stromal collagen organization. We used second harmonic generation (SHG) microscopy to investigate the differences in stromal collagen organization in rabbit eyes after corneal CXL in vivo as a function of depth and time after surgery. Methods: Rabbit corneas were treated in vivo with either riboflavin/UV radiation (UVX) or Rose Bengal/green light (RGX) and evaluated 1 and 2 months after CXL. Collagen fibers were imaged with a custom-built SHG scanning microscope through the central cornea (350 µm depth, 225 × 225 µm en face images). The order coefficient (OC), a metric for collagen organization, and total SHG signal were computed for each depth and compared between treatments. Results: OC values of CXL-treated corneas were larger than untreated corneas by 27% and 20% after 1 month and 38% and 33% after 2 months for the RGX and UVX, respectively. RGX OC values were larger than UVX OC values by 3% and 5% at 1 and 2 months. The SHG signal was higher in CXL corneas than untreated corneas, both at 1 and 2 months after surgery, by 18% and 26% and 1% and 10% for RGX and UVX, respectively. Conclusions: Increased OC corresponded with increased collagen fiber organization in CXL corneas. Changes in collagen organization parallel reported temporal changes in cornea stiffness after CXL and also, surprisingly, are detected deeper in the stroma than the regions stiffened by collagen cross-links.


Assuntos
Colágeno/metabolismo , Substância Própria/efeitos dos fármacos , Reagentes de Ligações Cruzadas , Corantes Fluorescentes/farmacologia , Fármacos Fotossensibilizantes/farmacologia , Riboflavina/farmacologia , Rosa Bengala/farmacologia , Animais , Substância Própria/metabolismo , Substância Própria/patologia , Feminino , Microscopia , Coelhos , Raios Ultravioleta
6.
Biomed Opt Express ; 11(11): 6337-6355, 2020 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-33282494

RESUMO

Corneal biomechanics play a fundamental role in the genesis and progression of corneal pathologies, such as keratoconus; in corneal remodeling after corneal surgery; and in affecting the measurement accuracy of glaucoma biomarkers, such as the intraocular pressure (IOP). Air-puff induced corneal deformation imaging reveals information highlighting normal and pathological corneal response to a non-contact mechanical excitation. However, current commercial systems are limited to monitoring corneal deformation only on one corneal meridian. Here, we present a novel custom-developed swept-source optical coherence tomography (SSOCT) system, coupled with a collinear air-puff excitation, capable of acquiring dynamic corneal deformation on multiple meridians. Backed by numerical simulations of corneal deformations, we propose two different scan patterns, aided by low coil impedance galvanometric scan mirrors that permit an appropriate compromise between temporal and spatial sampling of the corneal deformation profiles. We customized the air-puff module to provide an unobstructed SSOCT field of view and different peak pressures, air-puff durations, and distances to the eye. We acquired multi-meridian corneal deformation profiles (a) in healthy human eyes in vivo, (b) in porcine eyes ex vivo under varying controlled IOP, and (c) in a keratoconus-mimicking porcine eye ex vivo. We detected deformation asymmetries, as predicted by numerical simulations, otherwise missed on a single meridian that will substantially aid in corneal biomechanics diagnostics and pathology screening.

7.
Biomed Opt Express ; 9(1): 173-189, 2018 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-29359095

RESUMO

Many optical and biomechanical properties of the cornea, specifically the transparency of the stroma and its stiffness, can be traced to the degree of order and direction of the constituent collagen fibers. To measure the degree of order inside the cornea, a new metric, the order coefficient, was introduced to quantify the organization of the collagen fibers from images of the stroma produced with a custom-developed second harmonic generation microscope. The order coefficient method gave a quantitative assessment of the differences in stromal collagen arrangement across the cornea depths and between untreated stroma and cross-linked stroma.

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