Abstract
Abstract: :
Purpose: The precise arrangement of fibrillar collagen in the corneal stroma influences the tissue's transparency and dioptric power. The purpose of this study was to examine collagen fibril organisation in adult and foetal marmoset cornea in order to assess their potential as animal models for exploring corneal structure/function relationships. Methods: Wide-angle X-ray diffraction was used to map the orientations and proportions of aligned collagen fibrils over 3 whole adult and 2 whole (age-matched) foetal corneas at a maximum spatial resolution of 0.5 x 0.5mm. Small-angle X-ray diffraction also provided information on the average diameter and separation of the fibrils at 0.5mm intervals along 2 orthogonal corneal diameters. Results: Collagen orientation maps of all adult and 130 day (of a 144 day gestation term) foetal marmoset corneas clearly showed a circumferential annulus of fibrils at the limbus, similar to that observed previously in humans and some other vertebrate species. More centrally, the foetal corneas exhibited a predominantly orthogonal arrangement of fibrils reminiscent of that seen in mature human cornea and in immature tissue from some lower vertebrates. The current data suggests that the preferred orientation in the foetal marmoset cornea may be preserved in the adult tissue - a situation which has only been seen before in human cornea. An index of X-ray scattering intensity from aligned collagen as a fraction of total scattering intensity from all fibrillar collagen shows that in the foetal marmoset tissue approximately 20% of fibrils were preferentially aligned in the central cornea, compared to 45% at the limbus. For the adult tissue the corresponding values were 19% and 38%. Results of small-angle scattering revealed fibril separations and diameters for the adult and foetal tissues in the normal range for monkey cornea. Both parameters remained fairly constant across 2 orthogonal diameters of the cornea before increasing sharply at the limbus - a pattern similar to that observed in human cornea. Conclusions: This work represents the most comprehensive study of collagen organisation so far performed across whole, intact non-human corneas. Results so far suggest that, structurally, the human cornea may mirror that of the adult marmoset more closely than that of any other animal species so far studied. Although significant variation was evident in some of the data between adult specimens, this preliminary study has revealed the marmoset as a potentially useful subject for developing corneal models.
Keywords: cornea: basic science • cornea: stroma and keratocytes