Collagen fibrils appear more closely packed in the prepupillary cornea: optical and biomechanical implications.
OBJECTIVE
The size and organization of stromal collagen fibrils influence the biomechanical and optical properties of the cornea and hence its function. How fibrillar structure varies with position across the cornea has not been fully characterized. The present study was designed to quantify the collagen fibril spacing and diameter across the normal human cornea and to relate this to the properties of the tissue.


METHODS
Small-angle x-ray diffraction was used to map in detail the variation in fibril spacing and fibril diameter along orthogonal medial-lateral and inferior-superior meridians of five normal human corneoscleral discs.


RESULTS
Mean fibril diameters remained constant across all corneas up to the limbus, whereupon a sharp increase was observed. However, mean fibril spacing across the central 4 x 3 mm (prepupillary) cornea measured 5% to 7% lower than in the peripheral cornea.


CONCLUSIONS
Collagen fibrils in the prepupillary cornea appear to be more closely packed than in the peripheral cornea. Anisotropy in fibril packing across the cornea has potential implications for the transparency and refractive index of the tissue. Biomechanically, it is possible that the higher packing density of stress-bearing collagen fibrils in the prepupillary cornea is necessary for maintaining corneal strength, and hence curvature, in a region of reduced tissue thickness. By inference, these results could have important implications for the development of corneal models for refractive surgery.
Boote
Craig
C
Department of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom. bootec@cf.ac.uk
Dennis
Sally
S
Newton
Richard H
RH
Puri
Hina
H
Meek
Keith M
KM
D001696:Biomechanical Phenomena; D003094:Collagen / Q000737:chemistry* / Q000502:physiology; D003319:Corneal Stroma / Q000737:chemistry* / Q000502:physiology; D006801:Humans; D014961:X-Ray Diffraction
D003094:Collagen