Abstract
Purpose: :
Rge is an autosomal recessive disease of chicks that is characterized by progressive retinal dysfunction, secondary globe enlargement and functional blindness by ∼30 days post hatch. The corneas of rge chicks are abnormally thick and considerably flatter than those of normal chicks. The purpose of the current study was to investigate any potential differences in the organisation of stromal collagen between rge and normal chick corneas.
Methods: :
Wide–angle x–ray scattering, performed at station 14.1, Daresbury Synchrotron Source (Warrington, UK), was used to assess the organisation of stromal collagen in the cornea, limbus and adjacent sclera of a pair of eyes from a functionally blind rge chick (aged 9 months), and the left eye of an age–matched normal chick. The collagen fibril orientation and the relative distribution of collagen mass (both as an average through the full tissue thickness) were mapped at a spatial resolution of 0.4 mm.
Results: :
The arrangement of preferentially aligned collagen lamellae in the normal chick showed a broadly similar arrangement to that of the human cornea. In the central ∼ 3 mm of the cornea a preponderance of orthogonally arranged fibrils, directed along the superior–inferior and nasal–temporal meridians, is clearly evident. Towards the tissue periphery the preferential orientation of fibrils alters in favour of a more tangential arrangement. The data from the corneal periphery and limbus suggests the normal chick cornea is circumscribed by a highly reinforced fibril annulus. The orthogonal preferential arrangement of lamellae appeared well preserved in the central cornea of the rge chick. However, this feature extended considerably further from the corneal centre than in the control, and there was no evidence of a clear circum–corneal fibrillar annulus in either of the rge eyes examined.
Conclusions: :
Normal collagen fibril organisation is severely altered in the peripheral cornea and limbus of rge chicks. In the human eye the presence of a limbal annulus of fibrils has been suggested to contribute to corneal shape preservation. The current data indicate that corneal flattening in rge chicks may be due in part to remodelling of peripheral corneal/limbal collagen, rather than simply the result of mechanical stretching as the globe enlarges.
Keywords: cornea: stroma and keratocytes • cornea: clinical science • cornea: basic science