Kazaili, Ahmed
(2020)
Enzymatic degradation of the cornea to develop an experimental model for keratoconus: Biomechanical and optical characterisation.
Doctor of Philosophy thesis, University of Liverpool.
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Abstract
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. It is composed of five layers, in which the stroma is the thickest layer (approximately 90% of corneal thickness) that consists mainly of laminated collagen fibrils associated with proteoglycans. The cornea acts as the eye’s outermost lens that is accounted for approximately two-thirds of the eye's total optical power. Like other lenses, the cornea’s geometrical characteristics, such as the curvature, are important to maintain its functions for clear and stable vision. These geometrical characteristics are highly affected by the biomechanical properties of the cornea. For example, in keratoconus, the cornea is characterised by a progressive and localised thinning in corneal thickness, which is associated with a reduction in stiffness and other biomechanical properties. These alterations happen at the collagenous network, which is mainly responsible for the biomechanical features of the cornea, and are mostly attributed to genetic factors and abnormal enzymatic activity. Histological and biochemical studies suggested the role of amylase and collagenase activities in degradation of collagenous network and progression of keratoconus. However, the role of amylase and collagenase on biomechanical and optical properties have not been investigated. In this study, in vitro enzymatic degradation of porcine corneas was conducted with varying concentrations of α-amylase and collagenase (crude and purified) enzymes for different incubation periods. Several techniques, including atomic force microscopy, nanoindentation and optical coherence tomography, were utilised to assess the effect of the enzymes on biomechanical of corneal tissue at macroscale, microscale and nanoscale levels. Corneal transparency and absorption following enzymatic incubation were also measured using spectrophotometry. The biomechanical techniques that were utilised indicated that amylase and collagenase decrease corneal stiffness and thickness following incubation the corneas with amylase and collagenase. Further reduction in biomechanical properties and thickness of the corneas was found with increased enzymes concentrations and incubation periods. Corneal transparency was increased following incubation with the enzymes. The results suggest depletion of proteoglycans by amylase and digestion of collagen fibrils by collagenase. These results were used to propose an animal biomechanical model for keratoconus.
| Item Type: | Thesis (Doctor of Philosophy) |
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| Divisions: | Faculty of Science and Engineering > School of Engineering |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 14 Aug 2020 08:47 |
| Last Modified: | 18 Jan 2023 23:49 |
| DOI: | 10.17638/03090211 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3090211 |
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