Human Cornea Research Articles

A refined model on flow and oxygen consumption in the human cornea depending on the oxygen tension at the interface cornea/post lens tear film during contact lens wear

The study of oxygen consumption rate under” in vivo” human cornea during contact lens wear has been technically a challenge and several attempts have been made in the last 20 years to model the physiology of the human cornea during contact lens wear. Unfortunately, some of these models, based on a constant corneal oxygen consumption rate, produce areas on the cornea where the oxygen tension is negative, which has no physical sense. In order to avoid such inconsistency, different researchers have developed alternative models of oxygen consumption, which predict the likely oxygen metrics available at the interface cornea/post lens tear film by determination of oxygen flux, oxygen consumption, and oxygen tension through the different layers (endothelium, stroma, and epithelium). Although oxygen deficiency produces corneal edema, corneal swelling, hypoxia, acidosis, and other abnormalities, the estimation of the oxygen distribution below the impact of a contact lens wear is interesting to know which lens transmissibility was adequate to maintain the cornea and avoid epithelial and stromal anoxia. The estimation of minimum transmissibility for a lens for extended wear applications will be very useful for both clinicians and manufacturers. The aim of this work is to present a complete discussion based on Monod kinetics model that permits give an estimation of oxygen partial pressure distribution, the profile distribution of corneal flux and oxygen consumption rate, and finally the estimation of the relaxation mechanism of the cornea depending on the oxygen tension at the interface cornea/post lens tear film. Relaxation time in this context can quantify the capability of the corneal tissue to adapt to increasing concentrations of oxygen. It is proposed this parameter as a biological meaningful indicator of the interaction between contact lens polymers and living tissues such as the corneal cellular layer.

Identification of presumed corneal neuromas and microneuromas using laser-scanning in vivo confocal microscopy: a systematic review

Background/aimsThis systematic review critically evaluated peer-reviewed publications describing morphological features consistent with, or using terms related to, a ‘neuroma’ or ‘microneuroma’ in the human cornea using laser-scanning in vivo confocal...

Characterization of the transient mechanical properties of human cornea tissue using the tensile test simulation

There are potential problems in utilizing the material laws in numerical simulations due to the presence of both geometry nonlinearities and material nonlinearities. In this study, eight material parameters of the structural anisotropic fiber-reinforced hyper-viscoelastic model of Cornea with various fiber angles (8, 18, 22.5, and 45 degrees) have been obtained using coupled finite element-optimization analysis and experimental data. The utilized model considers the dispersion of the fibers along with their reorientation during loading, the nonlinear behavior of finite tissue deformation, and the intrinsic viscoelastic property of the matrix. The effect of each parameter on the sample responses in the tensile test simulation was examined. The results demonstrated that the J-shape behavior of the samples under the tensile test can be justified by the model used in the present study. Examining the results shows that the numerical simulations performed for the prediction of the cornea tissue behavior are nearly consistent with the experimental results and have good accuracy and that the model has acceptable stability. Therefore, an unprecedented opportunity has been provided to create numerical simulations for accurate prediction of corneal response to disease, injury, and surgery. The ability of the proposed model in predicting the human corneal behavior illustrates a promising future for numerical simulation in the corneal microsurgery field.

A decellularized human corneal scaffold for anterior corneal surface reconstruction

Allogenic transplants of the cornea are prone to rejection, especially in repetitive transplantation and in scarred or highly vascularized recipient sites. Patients with these ailments would particularly benefit from the possibility to use non-immunogenic decellularized tissue scaffolds for transplantation, which may be repopulated by host cells in situ or in vitro. So, the aim of this study was to develop a fast and efficient decellularization method for creating a human corneal extracellular matrix scaffold suitable for repopulation with human cells from the corneal limbus. To decellularize human donor corneas, sodium deoxycholate, deoxyribonuclease I, and dextran were assessed to remove cells and nuclei and to control tissue swelling, respectively. We evaluated the decellularization effects on the ultrastructure, optical, mechanical, and biological properties of the human cornea. Scaffold recellularization was studied using primary human limbal epithelial cells, stromal cells, and melanocytes in vitro and a lamellar transplantation approach ex vivo. Our data strongly suggest that this approach allowed the effective removal of cellular and nuclear material in a very short period of time while preserving extracellular matrix proteins, glycosaminoglycans, tissue structure, and optical transmission properties. In vitro recellularization demonstrated good biocompatibility of the decellularized human cornea and ex vivo transplantation revealed complete epithelialization and stromal repopulation from the host tissue. Thus, the generated decellularized human corneal scaffold could be a promising biological material for anterior corneal reconstruction in the treatment of corneal defects.

Changes of Corneal Biomechanical Properties upon Exclusive Ytt-/Sr-90 Irradiation of Pterygium.

Background: It is known that pterygia above a certain size cause astigmatism and other aberrations of the human cornea and thus impair the quality of vision. Exclusive Sr-/Ytt-90 beta irradiation is a highly effective treatment for primary pterygia. The aim of this retrospective study is to determine the extent to which higher order corneal aberrations are affected by this treatment. Methods: Evaluation of corneal topographies and wavefront aberration data of 20 primary pterygia patients generated before and at different points in time in the first year after irradiation. Additionally, the size of the pterygium was measured. Results: The study showed a significant increase in coma and triple leaf aberrations in pterygia with a horizontal length of 2 mm and more. It was also found that a pterygium size greater than 2 mm significantly induces astigmatism. Both phenomena reduce visual quality. In none of the patients could a pterygium recurrence be detected after irradiation. Conclusions: If the pterygium size is less than 2 mm, early exclusive Sr/Ytt-90 beta irradiation can be recommended. If the size is more than 2 mm, a pterygium excision 6 months after beta irradiation can be discussed.

Comparison of polarization sensitive second harmonic generation ‎microscopy techniques for the study of biological tissues

Recently, polarization sensitive Second Harmonic Generation (pSHG) microscopy has become a powerful tool for the study of the noncenterosymmetric biological structures. This is due to the fact that pSHG has some intrinsically benefits such as high resolution and contrast, and it can also penetrate deeply inside the sample in a noninvasive manner. One drawback for the pSHG technique is that the imaging procedure is not fast enough to study in vivo samples or to monitor the dynamics of different tissues. This issue imposes some limitations on using the pSHG technique to study in vivo samples. Fortunately, recently Single Scan polarization sensitive Second Harmonic Generation (SS-pSHG) technique has been introduced as a fast alternative for the conventional pSHG technique. In this article, the results obtained from ex vivo biological samples of starch, human cornea and animal tendon have been compared in a pixel-to-pixel manner using pSHG and SS-pSHG techniques in forward direction. Even though the samples used here are ex vivo, the results of this study promise that the polarization sensitive SHG microscopy techniques have a great potential to study biological tissues in a noninvasive procedure. This issue is more important especially in the cases that samples are in vivo.

Femtosecond Laser-Assisted Big-Bubble Deep Anterior Lamellar Keratoplasty.

PurposeTo determine whether type 1 big-bubble (BB) formation is influenced by the sequence of incisions created with the Victus femtosecond laser (FSL) enabled with software version 3.4 (SV 3.4) during deep anterior lamellar keratoplasty (DALK).Materials and MethodsConsecutive FSL-assisted DALK BB procedures were performed on 20 human donor corneas: 10 shaped by tunnel incision followed by lamellar incision (tunnel-lamellar group, TL) and 10 in the reverse order (lamellar-tunnel group, LT). The BB type was assessed by evaluating dynamic air movement during air inflation; bubble diameter and floor thickness were measured by anterior segment optical coherence tomography.ResultsOverall, a type 1 BB formed in 85% of eyes: 100% in the TL group and 70% in the LT group. In the LT group, a type 2 BB formed in 2 corneas and one cornea was perforated during cannula insertion. Type 1 BB was achieved after one attempt in 90% of eyes in the TL group and in 57% in the LT group.ConclusionShaping the tunnel before rather than after lamellar incision may be more effective for obtaining a type 1 BB by air injection.

Induction of CXCL10-Mediated Cell Migration by Different Types of Galectins.

Chemokines are an extended group of chemoattractant cytokines responsible for the recruitment of leukocytes into tissues. Among them, interferon-γ-inducible protein 10 (CXCL10) is abundantly expressed following inflammatory stimuli and participates in the trafficking of monocytes and activated T cells into sites of injury. Here, we report that different members of the galectin family of carbohydrate-binding proteins promote the expression and synthesis of CXCL10 independently of interferon-γ. Interestingly, CXCL10 induction was observed when galectins came in contact with stromal fibroblasts isolated from human cornea but not other cell types such as epithelial, monocytic or endothelial cells. Induction of CXCL10 by the tandem repeat galectin-8 was primarily associated with the chemotactic migration of THP-1 monocytic cells, whereas the prototype galectin-1 promoted the CXCL10-dependent migration of Jurkat T cells. These results highlight the potential importance of the galectin signature in dictating the recruitment of specific leukocyte populations into precise tissue locations.

The Human Tissue-Engineered Cornea (hTEC): Recent Progress.

Each day, about 2000 U.S. workers have a job-related eye injury requiring medical treatment. Corneal diseases are the fifth cause of blindness worldwide. Most of these diseases can be cured using one form or another of corneal transplantation, which is the most successful transplantation in humans. In 2012, it was estimated that 12.7 million people were waiting for a corneal transplantation worldwide. Unfortunately, only 1 in 70 patients received a corneal graft that same year. In order to provide alternatives to the shortage of graftable corneas, considerable progress has been achieved in the development of living corneal substitutes produced by tissue engineering and designed to mimic their in vivo counterpart in terms of cell phenotype and tissue architecture. Most of these substitutes use synthetic biomaterials combined with immortalized cells, which makes them dissimilar from the native cornea. However, studies have emerged that describe the production of tridimensional (3D) tissue-engineered corneas using untransformed human corneal epithelial cells grown on a totally natural stroma synthesized by living corneal fibroblasts, that also show appropriate histology and expression of both extracellular matrix (ECM) components and integrins. This review highlights contributions from laboratories working on the production of human tissue-engineered corneas (hTECs) as future substitutes for grafting purposes. It overviews alternative models to the grafting of cadaveric corneas where cell organization is provided by the substrate, and then focuses on their 3D counterparts that are closer to the native human corneal architecture because of their tissue development and cell arrangement properties. These completely biological hTECs are therefore very promising as models that may help understand many aspects of the molecular and cellular mechanistic response of the cornea toward different types of diseases or wounds, as well as assist in the development of novel drugs that might be promising for therapeutic purposes.

Femtosecond-Laser Assisted Surgery of the Eye: Overview and Impact of the Low-Energy Concept.

This article provides an overview of both established and innovative applications of femtosecond (fs)-laser-assisted surgical techniques in ophthalmology. Fs-laser technology is unique because it allows cutting tissue at very high precision inside the eye. Fs lasers are mainly used for surgery of the human cornea and lens. New areas of application in ophthalmology are on the horizon. The latest improvement is the high pulse frequency, low-energy concept; by enlarging the numerical aperture of the focusing optics, the pulse energy threshold for optical breakdown decreases, and cutting with practically no side effects is enabled.

Dependence of the heating effect on tissue absorption coefficient during corneal reshaping using different UV lasers: A numerical study

Corneal reshaping using laser ablation effect is a well-known ophthalmologic operation implemented to correct many vision disorders. UV pulsed lasers are utilized in this surgery due to their high absorption in corneal tissue without affecting the other parts of the eye. Ideally ablation may not be associated with heat transport, since high temperature is the enemy of soft tissues. However, the thermal effect of this procedure can cause tissue damage if the temperature rises above the safety level without appropriate handling. In the present study, we try to find the trade-off between efficient ablation and minimal temperature rise. So the thermal effect on the corneal tissue after applying five UV wavelengths; 193, 210, 213, 223 and 248nm has been simulated and investigated by solving Penne's bio-heat transfer equation using the finite element method. A 3D model of the human cornea is constructed using COMSOL Multiphysics computer software and the temperature rise is determined at the end of the laser pulse. The same spot size and pulse duration are used for each wavelength. While the absorption coefficient of the corneal tissue is the only variable as it is a wavelength dependent. The proposed results show that, the heating effect is directly proportional to the absorption coefficient. The highest recorded temperature was 259°C at 193nm, while, the minimum value was (70.1°C) recorded at 248nm at which the cornea has the lowest absorption coefficient.

Direct Evidence of Symmetry between Bilateral Human Corneas in Biomechanical Properties: A Comparison Study with Fresh Corneal Tissue

Purpose. To investigate the difference between the eyes from the same human with respect to the biomechanical properties of fresh corneal tissues and investigate the assumption of similarity of the corneal biomechanical properties between the eyes. Methods. Strip specimens extracted through a small incision lenticule extraction (SMILE) surgery were tested using a uniaxial tensile test. The specimens were extracted vertically. Low-strain tangent modulus (LSTM), high-strain tangent modulus (HSTM), and tensile strength (σb) were the biomechanical parameters used in the comparison of the eyes from the same human. Results. Ninety corneal specimens from 45 persons were included in this study. The LSTM of the left and right eyes were 1.34 ± 0.52 and 1.37 ± 0.46 MPa, while the HSTM were 50.53 ± 7.51 and 49.41 ± 7.01 MPa, respectively. There was no significant difference between the eyes in terms of LSTM, HSTM, andσbP=0.813, 0.335, and 0.605, resp.. The LSTM and HSTM were significantly correlated with the spherical equivalent (SE) (P≤0.01, P=0.001, resp.). Conclusions. The assumption that the corneal biomechanical properties of the eyes from the same human are similar has been confirmed for the first time using fresh human corneal tissue. This finding may be useful in further biomechanical studies.

Nonuniform Exposure to the Cornea from Millimeter Waves

This study examines the nonuniform exposure to the cornea from incident millimeter waves at 94-100 GHz. Two previous studies measured temperature increases in the rhesus cornea exposed to brief (1-6 s) pulses of high-fluence millimeter waves (94 GHz), one of which also estimated thresholds for corneal damage (reported as ED50, the dose resulting in a visible lesion 50% of the time). Both studies noted large variations in the temperature increase across the surface of the cornea due to wave interference effects. This study examines this variability using high-resolution simulations of mm-wave absorption and temperature increase in the human cornea from exposures to plane wave energy at 100 GHz. Calculations are based on an earlier study. The simulations show that the peak temperature increases in the cornea from short exposures (up to 10 s) to high-intensity mm-wave pulses are 1.7-2.8 times the median increase depending on the polarization of the incident energy. A simple one-dimensional "baseline" model provides a good estimate of the median temperature increase in the cornea. Two different estimates are presented for the thresholds for producing thermal lesions, expressed in terms of the minimum fluence of incident 100 GHz pulses. The first estimate is based on thresholds for thermal damage from pulsed infrared energy, and the second is based on a thermal damage model. The mm-wave pulses presently considered far exceed current IEEE or ICNIRP exposure limits but may be produced by some nonlethal weapons systems. Interference effects due to wave reflections from structures in and near the eye result in highly localized variations in energy absorbed in the cornea and surrounding facial tissues and are important to consider in a hazard analysis for exposures to intense pulsed millimeter waves.

CD23 mediated the induction of pro-inflammatory cytokines Interleukin-1 beta and tumor necrosis factors-alpha in Aspergillus fumigatus keratitis.

CD23 mediated the induction of pro-inflammatory cytokines Interleukin-1 beta and tumor necrosis factors-alpha in Aspergillus fumigatus keratitis.

The T414G mitochondrial DNA mutation: a biomarker of ageing in human eye.

The mitochondrial mutation T414G (mtDNAT414G) has been shown to accumulate in aged and sun-exposed skin. The human eye is also exposed to solar harmful rays. More precisely, the anterior structures of the eye (cornea, iris) filter UV rays and the posterior portion of the eye (retina) is exposed to visible light. These rays can catalyse mutations in mitochondrial DNA such as the mtDNAT414G, but the latter has never been investigated in the human ocular structures. In this study, we have developed a technique to precisely assess the occurrence of mtDNAT414G. Using this technique, we have quantified mtDNAT414G in different human ocular structures. We found an age-dependent accumulation of mtDNAT414G in the corneal stroma, the cellular layer conferring transparency and rigidity to the human cornea, and in the iris. Since cornea and iris are two anterior ocular structures exposed to solar UV rays, this suggests that the mtDNAT414G mutation is resulting from cumulative solar exposure and this could make the mtDNAT414G a good marker of solar exposure. We have previously shown that the mtDNACD4977 and mtDNA3895 deletions accumulate over time in photo-exposed ocular structures. With the addition of mtDNAT414G mutation, it becomes feasible to combine the levels of these different mtDNA mutations to obtain an accurate assessment of the solar exposure that an individual has accumulated during his/her lifetime.

Glutathione is a potential therapeutic target for acrolein toxicity in the cornea

Toxic and volatile chemicals are widely used in household products and previously used as warfare agents, causing a public health threat worldwide. This study aimed to evaluate the extent of injury and mechanisms of acrolein toxicity in the cornea. Primary human corneal stromal fibroblasts cultures (hCSFs) from human donor cornea were cultured and exposed to acrolein toxicity with -/+ N-acetylcysteine (NAC) to study the mode of action in the presence of Buthionine sulphoximine (BSO). PrestoBlue and MTT assays were used to optimize acrolein, NAC, and BSO doses for hCSFs. Cell-based assays and qRT-PCR analyses were performed to understand the acrolein toxicity and mechanisms. Acrolein exposure leads to an increased reactive oxygen species (ROS), compromised glutathione (GSH) levels, and mitochondrial dysfunction. The TUNEL and caspase assays showed that acrolein caused cell death in hCSFs. These deleterious effects can be mitigated using NAC in hCSFs, suggesting that GSH can be a potential target for acrolein toxicity in the cornea.

Animal model with structural similarity to human corneal collagen fibrillar arrangement.

Rabbit and porcine corneas have been used in scientific research due to their structural similarity to the human cornea. Currently, there are no studies that have compared corneal collagen fibrillar diameter, interfibrillar distance and interlamellar distance between human and animal models. Ten pairs of porcine, rabbit, and human corneas were used. These were analysed using light and Transmission Electron microscopy. The collagen fibrillar diameter, interfibrillar distance and interlamellar distance were statistically compared between porcine, rabbit and human corneas. The human, porcine and rabbit; mean collagen fibrillar diameters were: 24.52 ± 2.09nm; 32.87 ± 0.87nm; and 33.67 ± 1.97nm. The mean interfibrillar distances were: 46.10 ± 2.44nm; 53.33 ± 2.24nm; and 52.87 ± 2.73nm, respectively. The collagen fibrillar diameter and interfibrillar distance of porcine and rabbit corneas were significantly different (p < 0.001) to the human corneal values but not form each other. The interlamellar distance of human, porcine and rabbit corneas was: 2190 ± 820nm; 6460 ± 1180nm; and 4410 ± 1330nm, respectively. All the comparisons were statistically different, in porcine versus rabbit at the p < 0.01 level and both porcine and rabbit versus human at the p < 0.001 level. Histologically, all five layers (epithelium, Bowman's layer, stroma, Descemet membrane and endothelium) of the cornea were visible in all the three species. While neither animal model was structurally identical to the human cornea, they are both relatively close to being used as models to study the biomechanical effects of external insults/treatments to be extrapolated to the human cornea.

A Human Cornea-on-A-Chip for the Study of Epithelial Wound Healing by Extracellular Vesicles

Organs-on-chips are microfluidic devices for cell culturing to simulate tissue- or organ-level physiology and recapitulate their microenvironment, providing novel and significant solutions other than traditional animal tests. In vitro testing platforms for ocular biological studies have been increasingly used in preclinical efficacy and toxicity evaluation and prediction. Human cornea functions as a primary site of human eye exposure to environmental agents, requiring to establish a fully integrated cornea chip to study its biological characteristics. Here, we developed a microfluidic platform to mimic the human cornea and the complexity of its interface to the external environment. Our model consists of human corneal cells and a porous membrane embedded in the microfluidic platform, replicating the multi-scale structural organization and biological phenotype. Using this biomimetic system, we discovered and verified the fully integrated human cornea's barrier effects on the chip. Moreover, we developed an in vitro model of the corneal epithelial wound to understand cell-free therapy's efficacy using extracellular vesicles. We found that EVs derived from bone marrow-derived mesenchymal stem cells can significantly accelerate the corneal epithelial wound healing, and the decreased expression of matrix metallopeptidase 2 protein indicated that this method effectively inhibits corneal inflammation and angiogenesis. This work improves our ability to simulate the interaction between the human cornea and the external world in vitro and contribute to the future development of new screening platforms for biopharmaceuticals.

Refractive Index Measurement of Corneal-Shaped Hydrogel Material and Elasmobranch Corneas by Shack–Hartmann Wavefront Sensor System

The biocompatible hydrogel materials are used for the fabrication of artificial cornea. The refractive index of the hydrogel material can affect the optical quality of the artificial cornea. It is challenging to measure the refractive index of the hydrogel material because it is between solid and liquid status during the fabrication processes. In this work, we propose using the Shack-Hartmann wavefront sensor system to measure the wavefront images and to calculate the corresponding aberrations of optical material. The wavefront aberrations can be used to estimate the refractive index of the optical material. To prove the concept, the standard N-BK7 bi-convex lenses with focal lengths of 100 and 150 mm at wavelengths 780, 532, and 450 nm have been measured, and the results show that the relative errors of the average measured refractive indices are about 0.1%-0.17%. We used this proposed method to measure the refractive index of the P407-DA hydrogel material. We found that the average measured refractive indices of the P407-DA hydrogel material are 1.3175, 1.3516, and 1.3645 at wavelengths 780, 532, and 450 nm, respectively. Compared with the refractive index of human cornea, the P407-DA hydrogel can be used as the artificial cornea material. The Cauchy dispersion formula can be used to calculate the Abbe number of the P407-DA hydrogel material, which is about 11, lower than the human cornea's Abbe number. It means that the P407-DA hydrogel material has higher chromatic dispersion than the human cornea material. Moreover, the elasmobranch (shark) corneas, which are known as the suitable material for xenotransplantation, are measured by the Shack-Hartmann wavefront sensor system. The ABBE refractometer (ATAGO DR-M4) is used to measure the flat P407-DA hydrogel sample and it is found that the refractive index is slightly different when compared with the measured results by the Shack-Hartmann wavefront sensor system. The refractive indices of other biocompatible hydrogels poly(acrylic acid) (PAA) and poly(2-hydroxyethyl methacrylate) (PHEMA) are also measured by our proposed method, and it is found that the refractive index of P407-DA is more suitable for designing corneal samples than other hydrogels. It is found that the refractive indices of the elasmobranch corneas are similar to the P407-DA material. Our proposed method to measure the refractive index of hydrogel material using the Shack-Hartmann wavefront sensor system is useful. It is a non-contact, minimally invasive, and time-efficient method for shaped structures. The results can be used as a guide for developing better biocompatible material for artificial cornea.

Human cornea conservation in coconut water solution.

The aim of this study was to evaluate the physical and chemical characteristics of coconut water and to analyze the use of coconut water solution for the conservation of human corneas. This was an experimental and controlled study performed at the Eye Bank of the General Hospital of Fortaleza. The coconut water-based solution was prepared at the Goat Seed Technology Laboratory of the Department of Veterinary Medicine of the State University of Ceará. Discarded corneas from the Eye Bank were divided into two groups for sequential experiments: G1, coconut water-based solution (experimental group), and G2, conservative treatment with OPTISOL GS® (control group). The osmolality of corneas in G1 was analyzed sequentially at 275, 300, 325, 345, 365, and 400 mOsm/L. The viability of the corneas was determined by specular microscopy and biomicroscopy on the first, third, and seventh days. Corneas preserved in a solution of 365 and 345 mOsm/L had a transparency of 8 mm until the third day and had diffuse edema in the periphery, central folds, and partial epithelium loss until the seventh day. The 365-mOsm/L solution was associated with the worst results during follow-up. Corneas placed in Optisol-GS retained their original aspects. Coconut water-based preservative partially maintained corneal transparency and epithelial integrity, especially during the first three days of follow-up. The coconut water-based solutions used were not effective for use as preservatives in a human eye bank.