Abstract
Abstract: :
Purpose: (1) To map in detail the fibrillar arrangement and distribution of collagen in the primate cornea. (2) To compare the results with those obtained from human tissue. Methods:Wide angle X–ray diffraction was used to determine preferred lamellar direction and relative collagen mass (total and preferentially aligned) at 0.5 mm (horizontal) x 0.5 mm (vertical) intervals over 3 corneo–scleral disks from the common marmoset (Callithrix Jacchus). Results: There is a preferred lamellar orientation in the central marmoset cornea directed along the superior–inferior meridian. However, in contrast to humans, there is generally no accompanying preferential fibril alignment along the orthogonal nasal–temporal corneal meridian. Investigation of the central region of a further 16 marmoset corneas revealed that approximately 33% (+/– 1%) of fibrils lie within a 45o sector of the superior–inferior position. At the limbus the marmoset cornea features a circum–corneal annulus of highly aligned collagen, 0.5 – 1.5 mm wide, similar to that observed in humans. The width, fibril density, and fibril angular spread of the annulus all vary with circumferential position. Conclusions:Corneal structure in primates cannot be assumed to mirror that of humans, at least in terms of collagen architecture. The maps presented herein provide a control reference, and could be used to aid the interpretation of results from refractive surgery simulations using monkeys, and data from primate models of corneal disease. Optically, the contrasting lamellar arrangement in monkey and human cornea may account for the different birefringent properties of the two tissues. In humans it has been suggested that preferentially aligned collagen may exist, at least in part, to take up the stress of the rectus eye muscles along the corneal trajectories. However, from a biomechanical standpoint, the absence of extra fibrils along the nasal–temporal direction in marmoset cornea indicates a similar mechanism is unlikely in this primate. In monkeys, as in humans, a combination of a highly reinforced collagen annulus at the limbus and lamellar interplay in the anterior stroma could account for maintenance of corneal shape.
Keywords: cornea: stroma and keratocytes • cornea: basic science • optical properties