Structural control of corneal transparency, refractive power and dynamics

Meek, Keith M. ORCID: https://orcid.org/0000-0002-9948-7538, Knupp, Carlo ORCID: https://orcid.org/0000-0001-9127-2252, Lewis, Philip N. ORCID: https://orcid.org/0000-0002-3353-0708, Morgan, Siân R. and Hayes, Sally ORCID: https://orcid.org/0000-0001-8550-0108 2024. Structural control of corneal transparency, refractive power and dynamics. Eye 10.1038/s41433-024-02969-7

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Abstract

The cornea needs to be transparent to visible light and precisely curved to provide the correct refractive power. Both properties are governed by its structure. Corneal transparency arises from constructive interference of visible light due to the relatively ordered arrangement of collagen fibrils in the corneal stroma. The arrangement is controlled by the negatively charged proteoglycans surrounding the fibrils. Small changes in fibril organisation can be tolerated but larger changes cause light scattering. Corneal keratocytes do not scatter light because their refractive index matches that of the surrounding matrix. When activated, however, they become fibroblasts that have a lower refractive index. Modelling shows that this change in refractive index significantly increases light scatter. At the microscopic level, the corneal stroma has a lamellar structure, the parallel collagen fibrils within each lamella making a large angle with those of adjacent lamellae. X-ray scattering has shown that the lamellae have preferred orientations in the human cornea: inferior-superior and nasal-temporal in the central cornea and circumferential at the limbus. The directions at the centre of the cornea may help withstand the pull of the extraocular muscles whereas the pseudo-circular arrangement at the limbus supports the change in curvature between the cornea and sclera. Elastic fibres are also present; in the limbus they contain fibrillin microfibrils surrounding an elastin core, whereas at the centre of the cornea, they exist as thin bundles of fibrillin-rich microfibrils. We present a model based on the structure described above that may explain how the cornea withstands repeated pressure changes due to the ocular pulse.

Item Type:	Article
Date Type:	Published Online
Status:	In Press
Schools:	Optometry and Vision Sciences
Publisher:	Springer Nature [academic journals on nature.com]
ISSN:	0950-222X
Funders:	MRC
Date of First Compliant Deposit:	12 March 2024
Date of Acceptance:	26 January 2024
Last Modified:	16 Apr 2024 09:45
URI:	https://orca.cardiff.ac.uk/id/eprint/166548

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