Ultrastructure of the corneal stroma: a comparative study
Open accessAbstract
Using a high intensity synchrotron x-ray source, we have recorded diffraction over a range of angles from the corneas of a wide variety of species. The results show that the interfibrillar Bragg spacing varies from 39 nm to 67 nm, the fibril diameter varies from 24 nm to 43 nm, but in the species studied intermolecular Bragg spacing is constant (1.58 +/- 0.03 nm). Using these data, a number of other structural parameters were calculated including the interfibrillar volume, V, and the surface-to-surface fibril separation, S. Large variations were found, particularly between aquatic and terrestrial animals. We found that the parameter which appears to be most constant throughout the species was the volume fraction, that is, the proportion of the tissue occupied by the hydrated fibrils. Ignoring the volume of the stroma occupied by cells, the tissue fibril volume fraction was (28 +/- 3)% for both aquatic and land animals. The observation of a constant volume fraction led us to propose a simple model in which collagen molecules and interfibrillar glycosaminoglycans occur in a fixed ratio in all the species--thus species with narrow fibrils have fewer interfibrillar glycosaminoglycans and the fibrils are thus more closely spaced, and vice versa. This model agrees with many of the experimental data on corneal composition and on the physical properties of the tissue reported in the literature.
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There are about 300-400 triple-helical molecules within the cross-section of a corneal collagen fibril, depending on the species.
“There are about 300–400 triple-helical molecules within the cross-section of a fibril, depending on the species (Meek and Leonard, 1993, Holmes and Kadler, 2005)”
From Corneal structure and transparency (2015) · cites this paper as Meek and Leonard, 1993
The Results and Discussion (page unavailable) estimate the number of collagen molecules per fibril cross-section and say that this number differs between species. The accessible passage points to Table 3 for the estimates, but our copy does not provide readable table values establishing the claimed range of about 300–400. (LLM, conf=0.82)
Experimental — accuracy not yet measuredIn a study of over 40 animal species, including fish, birds, amphibians and mammals, Meek and Leonard (1993) reported that, despite wide inter-species variation of fibril diameters and centre-to-centre fibril spacings, the volume fraction (proportion of tissue occupied by hydrated fibrils and interfibrillar GAGs) was constant.
“in a study of over 40 animal species, including fish, birds, amphibians and mammals, Meek and Leonard (1993) reported that, even though there was a wide inter-species variation of fibril diameters and centre-to-centre fibril spacings, the volume fraction (i.e. the proportion of the tissue occupied by the hydrated fibrils and hence by the interfibrillar GAGs) was constant.”
From Corneal structure and transparency (2015) · cites this paper as Meek and Leonard (1993)
Because both polyanionic charge per unit volume and tissue hydration are constant between species regardless of PG composition, Meek and Leonard proposed a model in which fixed charges on GAGs are synthesised in proportion to total fibrillar collagen (types I and V); the larger the collagen fibrils, the greater the amount of fixed charge in the interfibrillar space, therefore the further apart the
“Because both polyanionic charge per unit volume and tissue hydration are constant between species, regardless of the PG composition (Scott and Bosworth, 1990, Gyi, 1988), they proposed a model in which the fixed charges on GAGs are synthesised in proportion to the total fibrillar collagen (types I and V) (Meek and Leonard, 1993); the larger the collagen fibrils, the greater amount of fixed charge”
From Corneal structure and transparency (2015) · cites this paper as Meek and Leonard, 1993
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Research works printed but not linked: 8
- Balazs, E. A. 1965. Amino sugar-containing macromolecules in the tissues of the eye and the ear. In The Amino Sugars: The Chemistry and Biology of Compounds Containing Amino Sugars. Vol. 2-A, Distribution and biological role. E. A. Balazs and R. W. Jeanloz, editors. Academic Press, New York. 401–460.
- Fitch, J. M., J. Gross, R. Mayne, B. Johnson-Wint, and T. F. Linsenmayer. 1984. Organisation of Collagen types I and V in the embryonic chicken cornea: Monoclonal antibody studies. Proc. Natl. Acad. Sci. USA. 81:2791–2795.
- Gyi, T. J., and K. M. Meek. 1987. Structural role of proteoglycans in the corneal stroma: a species study. Biochem. Soc. Trans. 15:1086– 1087.
- Gyi, T. J. 1988. A comparison of the structure of the corneal stroma in a variety of animal species. Ph.D. thesis, Open University, London.
- Maurice, D. M. 1969. The cornea and sclera. In The Eye. H. Davson, editor. Academic Press, New York. 489–599.
- Scott, J. E. 1991. Proteoglycan collagen interactions and corneal ultrastructure. Biochem. Soc. Trans. 19:877–881.
- Sivak, J. G. 1988. Corneal optics in aquatic animals: how they see above and below. In The Cornea: Transactions of the World Congress on the Cornea III. H. Dwight Cavanagh, editor. Raven Press, Ltd., New York. 181–186.
- Vainshtein, B. K. 1966. Diffraction of X-rays by Chain Molecules. Elsevier, Amsterdam, London, and New York.
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Corneal structure and transparency
Meek, K. M., & Knupp, C. (2015) · Progress in Retinal and Eye Research · doi:10.1016/j.preteyeres.2015.07.001 · Cited by 853 · see citing works
Self-citationStructural control of corneal transparency, refractive power and dynamics
Meek, K. M., Knupp, C., Lewis, P. N., Morgan, S. R., & Hayes, S. (2025) · Eye · doi:10.1038/s41433-024-02969-7 · Cited by 45 · see citing works
Self-citation
- Authors
- Meek, K. M., & Leonard, D. W.
- Affiliations
- The Open University (GB)
- ORCID
- Meek, K.M.
- Venue
- Biophysical Journal
- Publisher
- Elsevier BV
- Published
- 1993-01
- Volume
- 64
- Issue
- 1
- Pages
- 273-280
- ISSN
- 0006-3495 (ISSN-L)
- PMC
- PMC1262324
- OpenAlex
- W2036895638
- Cited by
- 166
- References
- 0
- Citations by year
- 2026: 4 · 2025: 9 · 2024: 3 · 2023: 6 · 2022: 4 · 2021: 5 · 2020: 7 · 2019: 4 · 2018: 1 · 2017: 5 · 2016: 9 · 2015: 9 · 2014: 7 · 2013: 8 · 2012: 3
- FWCI
- 1.89
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Licence
- Locations
- Biophysical Journal (publishedVersion)
- Europe PMC (PubMed Central) (publishedVersion)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- Funders
- Wellcome Trust
- Topics
- Health Sciences › Medicine › Radiology, Nuclear Medicine and Imaging › Corneal surgery and disorders
- Physical Sciences › Materials Science › Biomaterials › Collagen: Extraction and Characterization
- Health Sciences › Medicine › Radiology, Nuclear Medicine and Imaging › Corneal Surgery and Treatments
- Keywords
- corneal stroma, collagen fibrils, fibril diameter, glycosaminoglycans, cross-species comparison, corneal ultrastructure, synchrotron X-ray diffraction
- MeSH terms
- Animals, Biophysics, Collagen, Cornea, Glycosaminoglycans, Humans, Species Specificity, X-Ray Diffraction, Biophysical Phenomena
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