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Yazdani M. Tear film lipid layer and corneal oxygenation: a new function? Eye (Lond) 2023; 37:3534-3541. [PMID: 37138094 PMCID: PMC10686381 DOI: 10.1038/s41433-023-02557-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 03/22/2023] [Accepted: 04/20/2023] [Indexed: 05/05/2023] Open
Abstract
The classic model of tear film is composed of mucin layer, aqueous layer and the outermost tear film lipid layer (TFLL). The complex mixture of different classes of lipids, mainly secreted by meibomian glands, gives the TFLL unique physicochemical properties. Based on these properties, several functions of TFLL have been found and/or proposed such as the resistance to evaporation and facilitating the formation of a thin film. However, the role of TFLL in the oxygenation of the cornea, a transparent avascular tissue, has never been discussed in the literature. The continuous metabolic activity of the corneal surface and the replenishment of atmospheric gas creates an O2 gradient in the tear film. The molecules of O2 must therefore be transferred from the gas phase to the liquid phase through the TFLL. This process is a function of the diffusion and solubility of the lipid layer as well as interface transfer, which is influenced by alterations in the physical state and lipid composition. In the absence of research on TFLL, the present paper aims to bring the topic into the spotlight for the first time based on existing knowledge on O2 permeability of the lipid membranes and evaporation resistance of the lipid layers. The oxidative stress generated in perturbed lipid layers and the consequent adverse effects are also covered. The function of the TFLL proposed here intends to encourage future research in both basic and clinical sciences, e.g., opening new avenues for the diagnosis and treatment of ocular surface conditions.
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Affiliation(s)
- Mazyar Yazdani
- Department of Medical Biochemistry, Oslo University Hospital, Rikshospitalet, 0027, Oslo, Norway.
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2
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Li Q, Wong HL, Ip YL, Chu WY, Li MS, Saha C, Shih KC, Chan YK. Current microfluidic platforms for reverse engineering of cornea. Mater Today Bio 2023; 20:100634. [PMID: 37139464 PMCID: PMC10149412 DOI: 10.1016/j.mtbio.2023.100634] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 04/04/2023] [Accepted: 04/10/2023] [Indexed: 05/05/2023] Open
Abstract
According to the World Health Organization, corneal blindness constitutes 5.1% of global blindness population. Surgical outcomes have been improved significantly in the treatment of corneal blindness. However, corneal transplantation is limited by global shortage of donor tissue, prompting researchers to explore alternative therapies such as novel ocular pharmaceutics to delay corneal disease progression. Animal models are commonly adopted for investigating pharmacokinetics of ocular drugs. However, this approach is limited by physiological differences in the eye between animals and human, ethical issues and poor bench-to-bedside translatability. Cornea-on-a-chip (CoC) microfluidic platforms have gained great attention as one of the advanced in vitro strategies for constructing physiologically representative corneal models. With significant improvements in tissue engineering technology, CoC integrates corneal cells with microfluidics to recapitulate human corneal microenvironment for the study of corneal pathophysiological changes and evaluation of ocular drugs. Such model, in complement to animal studies, can potentially accelerate translational research, in particular the pre-clinical screening of ophthalmic medication, driving clinical treatment advancement for corneal diseases. This review provides an overview of engineered CoC platforms with respect to their merits, applications, and technical challenges. Emerging directions in CoC technology are also proposed for further investigations, to accentuate preclinical obstacles in corneal research.
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Aguilella-Arzo M, Compañ V. A three-dimensional model to describe complete human corneal oxygenation during contact lens wear. J Biomed Mater Res B Appl Biomater 2023; 111:610-621. [PMID: 36214217 PMCID: PMC10092785 DOI: 10.1002/jbm.b.35180] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Revised: 09/13/2022] [Accepted: 09/21/2022] [Indexed: 01/21/2023]
Abstract
We perform a novel 3D study to quantify the corneal oxygen consumption and diffusion in each part of the cornea with different contact lens materials. The oxygen profile is calculated as a function of oxygen tension at the cornea-tear interface and the oxygen transmissibility of the lens, with values used in previous studies. We aim to determine the influence of a detailed geometry of the cornea in their modeling compared to previous low dimensional models used in the literature. To this end, a 3-D study based on an axisymmetric volume element analysis model was applied to different contact lenses currently on the market. We have obtained that the model provides a valuable tool for understanding the flux and cornea oxygen profiles through the epithelium, stroma, and endothelium. The most important results are related to the dependence of the oxygen flux through the cornea-lens system on the contact lens thickness and geometry. Both parameters play an important role in the corneal flux and oxygen tension distribution. The decline in oxygen consumption experienced by the cornea takes place just inside the epithelium, where the oxygen tension falls to between 95 and 16 mmHg under open eye conditions, and 30 to 0.3 mmHg under closed eye conditions, depending on the contact lens worn. This helps to understand the physiological response of the corneal tissue under conditions of daily and overnight contact lens wear, and the importance of detailed geometry of the cornea in the modeling of diffusion for oxygen and other species.
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Affiliation(s)
| | - Vicente Compañ
- Departamento de Termodinámica Aplicada. Escuela Técnica Superior de Ingenieros Industriales (ETSII), Universitat Politècnica de València, Valencia, Spain
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Sun Q, Ma L, Ferreira F, Brown C, Reid B, Zhao M. Optic Fiber Microsensor Reveals Specific Spatiotemporal Oxygen Uptake Profiles at the Mammalian Ocular Surface. BIOSENSORS 2023; 13:245. [PMID: 36832011 PMCID: PMC9954666 DOI: 10.3390/bios13020245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 02/02/2023] [Accepted: 02/07/2023] [Indexed: 06/18/2023]
Abstract
Oxygen (O2) uptake by cells and tissues is a critical indicator of metabolic demand, changes in microenvironment, and pathophysiology. O2 uptake from the atmosphere accounts for virtually all the O2 consumption in the avascular cornea; however, a detailed spatiotemporal profile of corneal O2 uptake (COU) remains undetermined. Here, we used a non-invasive self-referencing optical fiber O2 sensor-the scanning micro-optrode technique (SMOT)-to report the O2 partial pressure and flux variations at the ocular surface of rodents and non-human primates. In vivo spatial mapping in mice revealed a distinct COU, characterized by a centripetal gradient with a significantly higher O2 influx at the limbus and conjunctiva regions than at the center of the cornea. This regional COU profile was reproduced ex vivo in freshly enucleated eyes. The centripetal gradient was conserved across the following species analyzed: mice, rats, and rhesus monkeys. In vivo temporal mapping in mice showed a significant increase in the O2 flux in the limbus in the evening compared to other times. Altogether, the data unveiled a conserved centripetal COU profile, which may be associated with the limbal epithelial stem cells residing at the intersection of the limbus and conjunctiva. These physiological observations will serve as a useful baseline for comparative studies with contact lens wear, ocular disease, diabetes, etc. Moreover, the sensor may be applied to understand the responses of the cornea and other tissues to various insults, drugs, or changes in the environment.
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Affiliation(s)
- Qin Sun
- Department of Dermatology, Institute for Regenerative Cures, School of Medicine, University of California, Davis, CA 95816, USA
- School of Life Science, Yunnan Normal University, Kunming 650092, China
| | - Li Ma
- Department of Dermatology, Institute for Regenerative Cures, School of Medicine, University of California, Davis, CA 95816, USA
| | - Fernando Ferreira
- Department of Dermatology, Institute for Regenerative Cures, School of Medicine, University of California, Davis, CA 95816, USA
- Departamento de Biologia, Centro de Biologia Molecular e Ambiental (CMBA), Universidade do Minho, 4710-057 Braga, Portugal
| | - Chelsea Brown
- Department of Ophthalmology & Vision Science, Institute for Regenerative Cures, School of Medicine, University of California, Davis, CA 95816, USA
| | - Brian Reid
- Department of Dermatology, Institute for Regenerative Cures, School of Medicine, University of California, Davis, CA 95816, USA
- Department of Ophthalmology & Vision Science, Institute for Regenerative Cures, School of Medicine, University of California, Davis, CA 95816, USA
| | - Min Zhao
- Department of Dermatology, Institute for Regenerative Cures, School of Medicine, University of California, Davis, CA 95816, USA
- Department of Ophthalmology & Vision Science, Institute for Regenerative Cures, School of Medicine, University of California, Davis, CA 95816, USA
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Nioi M, Napoli PE, Demontis R, Chighine A, De-Giorgio F, Grassi S, Scorcia V, Fossarello M, d’Aloja E. The Influence of Eyelid Position and Environmental Conditions on the Corneal Changes in Early Postmortem Interval: A Prospective, Multicentric OCT Study. Diagnostics (Basel) 2022; 12:diagnostics12092169. [PMID: 36140570 PMCID: PMC9497849 DOI: 10.3390/diagnostics12092169] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Revised: 08/18/2022] [Accepted: 08/31/2022] [Indexed: 11/16/2022] Open
Abstract
In the current study, using portable optical coherence tomography, we evaluated 46 corneas of 23 individuals in a multicenter setting during the first 17 h after death. Twenty-three eyes were kept open, and twenty three were kept closed. Furthermore, the experiment was carried out for 12 samples in summer and 11 in winter. Our data show that postmortem corneal alterations largely depend on the phenomena of dehydration (in particular in open eyes) and swelling of the stroma in closed eyes, probably due in the first phase to hypoxia/anoxia and subsequently to the passage by osmosis of the aqueous humor from the anterior chamber to the corneal tissue. Our findings could have significant repercussions in forensic pathology for estimating the postmortem interval and transplantation to optimize the conservation of the tissue before the explant.
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Affiliation(s)
- Matteo Nioi
- Forensic Medicine Unit, Department of Clinical Sciences and Public Health, University of Cagliari, 09124 Cagliari, Italy
- Correspondence: (M.N.); (P.E.N.)
| | - Pietro Emanuele Napoli
- Eye Clinic, Department of Surgical Science, University of Cagliari, 09124 Cagliari, Italy
- Correspondence: (M.N.); (P.E.N.)
| | - Roberto Demontis
- Forensic Medicine Unit, Department of Clinical Sciences and Public Health, University of Cagliari, 09124 Cagliari, Italy
| | - Alberto Chighine
- Forensic Medicine Unit, Department of Clinical Sciences and Public Health, University of Cagliari, 09124 Cagliari, Italy
| | - Fabio De-Giorgio
- Legal Medicine, Department of Health Surveillance and Bioethics, Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario Agostino Gemelli IRCCS, 00168 Rome, Italy
| | - Simone Grassi
- Legal Medicine, Department of Health Surveillance and Bioethics, Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario Agostino Gemelli IRCCS, 00168 Rome, Italy
- Section of Forensic Medical Sciences, Department of Health Sciences, University of Florence, 50121 Florence, Italy
| | - Vincenzo Scorcia
- Department of Ophthalmology, University ‘Magna Græcia’ of Catanzaro, Viale Europa, 88100 Catanzaro, Italy
| | - Maurizio Fossarello
- Eye Clinic, Department of Surgical Science, University of Cagliari, 09124 Cagliari, Italy
| | - Ernesto d’Aloja
- Forensic Medicine Unit, Department of Clinical Sciences and Public Health, University of Cagliari, 09124 Cagliari, Italy
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Moreno VC, Aguilella-Arzo M, Del Castillo RM, Espinós FJ, Del Castillo LF. 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. JOURNAL OF OPTOMETRY 2022; 15:160-174. [PMID: 33589396 PMCID: PMC9068744 DOI: 10.1016/j.optom.2020.12.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 12/04/2020] [Accepted: 12/29/2020] [Indexed: 05/23/2023]
Abstract
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.
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Affiliation(s)
- Vicente Compañ Moreno
- Departmento de Termodinámica Aplicada. Escuela Técnica Superior de Ingenieros Industriales (ETSII), Universitat Politécnica de Valencia, Campus de Vera s / n, 46020 Valencia, Spain
| | | | - Roxana M Del Castillo
- Departamento de Física, Facultad de Ciencias, Universidad Nacional Autónoma de México, Mexico City 04510, Mexico
| | - Francisco J Espinós
- Centro de Investigación en Acuicultura y Medio Ambiente (ACUMA), Universitat Politècnica de València, Campus de Vera s / n, 46020 Valencia, Spain
| | - Luis Felipe Del Castillo
- Department of Polymers, Materials Research Institute, National Autonomous University of Mexico, Ap Postal 70-360, Coyoacan, Mexico City, Mexico
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Di Zazzo A, Gaudenzi D, Yin J, Coassin M, Fernandes M, Dana R, Bonini S. Corneal angiogenic privilege and its failure. Exp Eye Res 2021; 204:108457. [PMID: 33493471 PMCID: PMC10760381 DOI: 10.1016/j.exer.2021.108457] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 01/13/2021] [Accepted: 01/18/2021] [Indexed: 12/16/2022]
Abstract
The cornea actively maintains its own avascular status to preserve its ultimate optical function. This corneal avascular state is also defined as "corneal angiogenic privilege", which results from a critical and sensitive balance between anti-angiogenic and pro-angiogenic mechanisms. In our review, we aim to explore the complex equilibrium among multiple mediators which prevents neovascularization in the resting cornea, as well as to unveil the evolutive process which leads to corneal angiogenesis in response to different injuries.
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Affiliation(s)
- Antonio Di Zazzo
- Ophthalmology Operative Complex Unit, University Campus Bio-Medico, Rome, Italy.
| | - Daniele Gaudenzi
- Ophthalmology Operative Complex Unit, University Campus Bio-Medico, Rome, Italy
| | - Jia Yin
- Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
| | - Marco Coassin
- Ophthalmology Operative Complex Unit, University Campus Bio-Medico, Rome, Italy
| | - Merle Fernandes
- Cornea and Anterior Segment Services, LV Prasad Eye Institute, GMR Varalakshmi Campus, Visakhapatnam, India
| | - Reza Dana
- Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
| | - Stefano Bonini
- Ophthalmology Operative Complex Unit, University Campus Bio-Medico, Rome, Italy
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Abstract
PURPOSE Oxygen is essential for aerobic mammalian cell physiology. Oxygen tension (PO2) should reach a minimum at some position within the corneal stroma, and oxygen flux should be zero, by definition, at this point as well. We found the locations and magnitudes of this "corneal equilibrium flux" (xmin) and explored its physiological implications. METHODS We used an application of the Monod kinetic model to calculate xmin for normal human cornea as anterior surface PO2 changes from 155 to 20 mmHg. RESULTS We find that xmin deepens, broadens, and advances from 1.25 μm above the endothelial-aqueous humor surface toward the epithelium (reaching a position 320 μm above the endothelial-aqueous humor surface) as anterior corneal surface PO2 decreases from 155 to 20 mmHg. CONCLUSIONS Our model supports an anterior corneal oxygen flux of 9 μL O2 · cm · h and an epithelial oxygen consumption of approximately 4 μL O2 · cm · h. Only at the highest anterior corneal PO2 does our model predict that oxygen diffuses all the way through the cornea to perhaps reach the anterior chamber. Of most interest, corneal oxygen consumption should be supported down to a corneal surface PO2 of 60 to 80 mmHg but declines below this range. We conclude that the critical oxygen tension for hypoxia induced corneal swelling is more likely this range rather than a fixed value.
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10
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The significance of oxygen during contact lens wear. Cont Lens Anterior Eye 2014; 37:394-404. [DOI: 10.1016/j.clae.2014.07.012] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 07/19/2014] [Accepted: 07/22/2014] [Indexed: 11/30/2022]
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LEI YULIN, ZHENG XIUYUN, HOU JIE, XU BAOZENG, MU GUOYING. Effects of long-term soft contact lens wear on the corneal thickness and corneal epithelial thickness of myopic subjects. Mol Med Rep 2014; 11:2020-6. [DOI: 10.3892/mmr.2014.2964] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 08/06/2014] [Indexed: 11/05/2022] Open
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