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Swelling of normal and pathological corneal stroma

Khan, Shukria, Akhtar, Saeed and Meek, Keith Michael Andrew ORCID: 2002. Swelling of normal and pathological corneal stroma. Fibre Diffraction Review 10 , p. 83.

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PURPOSE. Corneas swollen in vitro, at physiological pH with a bounding membrane will remain transparent even at pH8 (Huang Y and Meek KM, Biophysics J. 77, 1655-1665,1999) while corneas swollen in vivo become opaque. Our purpose was to compare the swelling of Fuchs' dystrophy and normal corneas to explain this anomalous behaviour. METHOD. Experiment 1: Bovine corneas were swollen at pH 8 and pH 5 and final pH3.2 and pH5 using a bounding membrane. Experiment 2 : Normal and Fuchs’ dystrophy corneas were either swollen by addition of physiological saline or were equilibrated against different concentration of polyethylene glycol (PEG)in phosphate buffer to a range of final hydrations. The corneas were examined by x-ray diffraction (XRD) and transmission electron microscopy (TEM). RESULTS. Experiment 1: At pH 8 the corneas at both hydrations appeared clear while at pH 5 the corneas at both hydrations appeared opaque. XRD revealed no correlation between collagen interfibrillar spacing, fibrilar diameter and appearance of tissue. But a correlation was observed between degree oforder of the fibril packing and appearance of tissue. A high degree of order was found in the clear corneas while a low degree of order occurred in opaque corneas. Experiment 2: Both normal and Fuchs’ dystrophy corneas swelled on addition of saline. All saline-swollen corneaswere opaque. Although the final hydrations were different, XRD revealed there was little difference in interfibrillar spacing between Fuchs’ dystrophy and normal corneas, but a low degree of fibril packing order was observed. TEM revealed the presence of numerous large intra-lamellar ’lakes’. CONCLUSION. Corneas swollen in vitro appear opaque because of the formation of collagen-free ’lakes’ and an accompanying disordering of the fibril packing. Swelling with a bounding membrane in the region of neutral pH can reduce these effects and allow a more even water distribution and hence a clearer cornea.Differences in the swelling behaviour of normal and Fuchs' dystrophy corneas may relate to compositional changes in the source of the osmotic force controlling hydration (probably including changes in proteoglycans) manifested here by a different response to equilibration against PEG. The X-ray diffraction and electron microscope results suggest the presence of more ’lake’ formation as the Fuchs' cornea swells (compared to the swollen normal cornea) perhaps for the same reasons. The distribution of tissue water, and hence the resulting light scattering in Fuchs' dystrophy corneas, is probably a consequence of these compositional changes, which do not occur when normal corneas are swollen in vitro near neutral pH with a bounding membrane.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Optometry and Vision Sciences
Subjects: R Medicine > RE Ophthalmology
Uncontrolled Keywords: Fuchs'dystrophy ; Eye: cornea
ISSN: 1463-8401
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Last Modified: 17 Oct 2022 09:40

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