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Fontanella CG, Carniel EL, Corain L, Peruffo A, Iacopetti I, Pavan PG, Todros S, Perazzi A. Mechanical behaviour of healthy versus alkali-lesioned corneas by a porcine organ culture model. BMC Vet Res 2021; 17:340. [PMID: 34711207 PMCID: PMC8555156 DOI: 10.1186/s12917-021-03050-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Accepted: 09/24/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Cornea is a composite tissue exhibiting nonlinear and time-dependent mechanical properties. Corneal ulcers are one of the main pathologies that affect this tissue, disrupting its structural integrity and leading to impaired functions. In this study, uniaxial tensile and stress-relaxation tests are developed to evaluate stress-strain and time-dependent mechanical behaviour of porcine corneas. RESULTS The samples are split in two groups: some corneas are analysed in an unaltered state (healthy samples), while others are injured with alkaline solution to create an experimental ulcer (lesioned samples). Furthermore, within each group, corneas are examined in two conditions: few hours after the enucleation (fresh samples) or after 7 days in a specific culture medium for the tissue (cultured samples). Finally, another condition is added: corneas from all the groups undergo or not a cross-linking treatment. In both stress-strain and stress-relaxation tests, a weakening of the tissue is observed due to the imposed conditions (lesion, culture and treatment), represented by a lower stiffness and increased stress-relaxation. CONCLUSIONS Alkali-induced corneal stromal melting determines changes in the mechanical response that can be related to a damage at microstructural level. The results of the present study represent the basis for the investigation of traditional and innovative corneal therapies.
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Affiliation(s)
- Chiara Giulia Fontanella
- Department of Industrial Engineering, University of Padova, via Venezia 1, 35131, Padova, Italy.,Centre for Mechanics of Biological Materials, University of Padova, via Marzolo 9, 35131, Padova, Italy
| | - Emanuele Luigi Carniel
- Department of Industrial Engineering, University of Padova, via Venezia 1, 35131, Padova, Italy.,Centre for Mechanics of Biological Materials, University of Padova, via Marzolo 9, 35131, Padova, Italy
| | - Livio Corain
- Department of Management and Engineering, University of Padova, stradella S. Nicola 3, 36100, Vicenza, Italy
| | - Antonella Peruffo
- Department of Comparative Biomedicine and Food Science, University of Padova, viale dell'Università 16, Legnaro, 35020, Padova, Italy
| | - Ilaria Iacopetti
- Department of Animal Medicine, Production and Health, University of Padova, viale dell'Università 16, Legnaro, 35020, Padova, Italy
| | - Piero G Pavan
- Department of Industrial Engineering, University of Padova, via Venezia 1, 35131, Padova, Italy.,Centre for Mechanics of Biological Materials, University of Padova, via Marzolo 9, 35131, Padova, Italy
| | - Silvia Todros
- Department of Industrial Engineering, University of Padova, via Venezia 1, 35131, Padova, Italy. .,Centre for Mechanics of Biological Materials, University of Padova, via Marzolo 9, 35131, Padova, Italy.
| | - Anna Perazzi
- Department of Animal Medicine, Production and Health, University of Padova, viale dell'Università 16, Legnaro, 35020, Padova, Italy
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Blackburn BJ, Rollins AM, Dupps WJ. Biomechanics of Ophthalmic Crosslinking. Transl Vis Sci Technol 2021; 10:8. [PMID: 34328498 PMCID: PMC8327749 DOI: 10.1167/tvst.10.5.8] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2021] [Accepted: 06/19/2021] [Indexed: 12/12/2022] Open
Abstract
Crosslinking involves the formation of bonds between polymer chains, such as proteins. In biological tissues, these bonds tend to stiffen the tissue, making it more resistant to mechanical degradation and deformation. In ophthalmology, the crosslinking phenomenon is being increasingly harnessed and explored as a treatment strategy for treating corneal ectasias, keratitis, degenerative myopia, and glaucoma. This review surveys the multitude of exogenous crosslinking strategies reported in the literature, both "light" (involving light energy) and "dark" (involving non-photic chemical processes), and explores their mechanisms, cytotoxicity, and stage of translational development. The spectrum of ophthalmic applications described in the literature is then discussed, with particular attention to proposed therapeutic mechanisms in the cornea and sclera. The mechanical effects of crosslinking are then discussed in the context of their proposed site and scale of action. Biomechanical characterization of the crosslinking effect is needed to more thoroughly address knowledge gaps in this area, and a review of reported methods for biomechanical characterization is presented with an attempt to assess the sensitivity of each method to crosslinking-mediated changes using data from the experimental and clinical literature. Biomechanical measurement methods differ in spatial resolution, mechanical sensitivity, suitability for detecting crosslinking subtypes, and translational readiness and are central to the effort to understand the mechanistic link between crosslinking methods and clinical outcomes of candidate therapies. Data on differences in the biomechanical effect of different crosslinking protocols and their correspondence to clinical outcomes are reviewed, and strategies for leveraging measurement advances predicting clinical outcomes of crosslinking procedures are discussed. Advancing the understanding of ophthalmic crosslinking, its biomechanical underpinnings, and its applications supports the development of next-generation crosslinking procedures that optimize therapeutic effect while reducing complications.
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Affiliation(s)
- Brecken J. Blackburn
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA
| | - Andrew M. Rollins
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA
| | - William J. Dupps
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA
- Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH, USA
- Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA
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Hersh PS, Lai MJ, Gelles JD, Lesniak SP. Transepithelial corneal crosslinking for keratoconus. J Cataract Refract Surg 2019; 44:313-322. [PMID: 29703286 DOI: 10.1016/j.jcrs.2017.12.022] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2017] [Revised: 11/17/2017] [Accepted: 12/10/2017] [Indexed: 12/13/2022]
Abstract
PURPOSE To evaluate outcomes of corneal crosslinking (CXL) using a transepithelial technique for the treatment of keratoconus. SETTING Cornea and refractive surgery subspecialty practice. DESIGN Prospective case series. METHODS Transepithelial CXL was performed in keratoconic eyes using riboflavin 0.1% and topical anesthetic containing benzalkonium chloride to facilitate riboflavin diffusion through the epithelium. Eyes were randomized to receive riboflavin administration either every 1 minute or every 2 minutes during ultraviolet-A exposure at 3mW/cm2. The principal outcome was change in maximum keratometry (K) and secondary outcomes included uncorrected (UDVA) and corrected (CDVA) distance visual acuities, mean K, and comparison of randomized groups. RESULTS Eighty-two eyes of 56 patients were treated. At 1 year, maximum K decreased significantly by 0.45 diopters (D) ± 1.94 (SD); it improved by 2.0 D or more in 11 eyes (13%) and worsened by 2.0 D or more in 4 eyes (5%). The mean UDVA significantly improved by 0.7 lines, whereas the CDVA improved by 0.2 lines. Two eyes showed both continued progression with loss of CDVA. Only the 1-minute subgroup showed significant improvements in maximum K (-0.73 D) and UDVA. Transient corneal erosion and epitheliopathy were reported in 21% of eyes. CONCLUSIONS Transepithelial CXL resulted in significant improvements in maximum K and UDVA over 1 year. There was a suggestion that increased riboflavin dosing might improve procedure outcomes. Further study is required to determine the relative advantages and disadvantages of different transepithelial approaches to the standard CXL protocol with epithelial removal.
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Affiliation(s)
- Peter S Hersh
- From the Cornea and Laser Eye Institute-Hersh Vision Group (Hersh), CLEI Center for Keratoconus (Hersh, Lai, Gelles), Teaneck, and the Department of Ophthalmology, Rutgers-New Jersey Medical School (Hersh, Lesniak), Newark, New Jersey, USA.
| | - Michael J Lai
- From the Cornea and Laser Eye Institute-Hersh Vision Group (Hersh), CLEI Center for Keratoconus (Hersh, Lai, Gelles), Teaneck, and the Department of Ophthalmology, Rutgers-New Jersey Medical School (Hersh, Lesniak), Newark, New Jersey, USA
| | - John D Gelles
- From the Cornea and Laser Eye Institute-Hersh Vision Group (Hersh), CLEI Center for Keratoconus (Hersh, Lai, Gelles), Teaneck, and the Department of Ophthalmology, Rutgers-New Jersey Medical School (Hersh, Lesniak), Newark, New Jersey, USA
| | - Sebastian P Lesniak
- From the Cornea and Laser Eye Institute-Hersh Vision Group (Hersh), CLEI Center for Keratoconus (Hersh, Lai, Gelles), Teaneck, and the Department of Ophthalmology, Rutgers-New Jersey Medical School (Hersh, Lesniak), Newark, New Jersey, USA
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Abstract
PURPOSE There has been a recent explosion in the variety of techniques used to accomplish corneal cross-linking (CXL) for the treatment of ectatic corneal diseases. To understand the success or failure of various techniques, we review the physicochemical basis of corneal CXL and re-evaluate the current principles and long-standing conventional wisdom in the light of recent, compelling, and sometimes contradictory research. METHODS Two clinicians and a medicinal chemist developed a list of current key topics, controversies, and questions in the field of corneal CXL based on information from current literature, medical conferences, and discussions with international practitioners of CXL. RESULTS Standard corneal CXL with removal of the corneal epithelium is a safe and efficacious procedure for the treatment of corneal ectasias. However, the necessity of epithelium removal is painful for patients, involves risk and requires significant recovery time. Attempts to move to transepithelial corneal CXL have been hindered by the lack of a coherent understanding of the physicochemistry of corneal CXL. Misconceptions about the applicability of the Bunsen-Roscoe law of reciprocity and the Lambert-Beer law in CXL hamper the ability to predict the effect of ultraviolet A energy during CXL. Improved understanding of CXL may also expand the treatment group for corneal ectasia to those with thinner corneas. Finally, it is essential to understand the role of oxygen in successful CXL. CONCLUSIONS Improved understanding of the complex interactions of riboflavin, ultraviolet A energy and oxygen in corneal CXL may provide a successful route to transepithelial corneal CXL.
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