Spatial Patterns and Age-Related Changes of the Collagen Crimp in the Human Cornea and Sclera

Abstract

PurposeCollagen is the main load-bearing component of the eye, and collagen crimp is a critical determinant of tissue mechanical behavior. We test the hypothesis that collagen crimp morphology varies over the human cornea and sclera and with age.MethodsWe analyzed 42 axial whole-globe sections from 20 normal eyes of 20 human donors, ranging in age from 0.08 (1 month) to 97 years. The sections were imaged using polarized light microscopy to obtain μm-scale fiber bundle/lamellae orientation from two corneal and six scleral regions. Crimp morphology was quantified through waviness, tortuosity, and amplitude.ResultsWhole-globe median waviness, tortuosity, and amplitude were 0.127 radians, 1.002, and 0.273 μm, respectively. These parameters, however, were not uniform over the globe, instead exhibiting distinct, consistent patterns. All crimp parameters decreased significantly with age, with significantly different age-related decreases between regions. The crimp morphology of the limbus changed the most drastically with age, such that it had the largest crimp in neonates, and among the smallest in the elderly.ConclusionsAge-related decreases in crimp parameters are likely one of the mechanisms underlying age-related stiffening of the sclera and cornea, potentially influencing sensitivity to IOP. Further work is needed to determine the biomechanical implications of the crimp patterns observed. The comparatively large changes in the crimp morphology of the limbus, especially in the early years of life, suggest that crimp in this region may play a role in eye development, although the exact nature of this is unclear.

Thin Lamina Cribrosa Beams Have Different Collagen Microstructure Than Thick Beams

“…1 ). 26 – 31 Briefly, two filters (Hoya, Tokyo, Japan) were used, one as a polarizer, and the other as an analyzer. Four images were acquired using white light illumination, with filter orientations rotated 45° between images.…”

“… 32 To facilitate visualization, we also computed an “energy” parameter. 26 – 31 Briefly, this parameter measures the variations in pixel intensity with rotations of the polarized filter. If there is no birefringent material (e.g., zero collagen density), the energy will be zero.…”

“…3 ). 26 , 28 , 29 , 31 Briefly, crimp waviness was computed as the circular standard deviation of the orientation values (θ) of the pixels underlying the longitudinal line, in absolute values. Crimp tortuosity was computed as the ratio of the sum of the pixels' path length components to the sum of the end-to-end length components.…”

“…For this, we used techniques based on polarized light microscopy (PLM) that we have recently demonstrated as suitable for direct measurement of collagen crimp in ocular tissues. 26 – 31 …”

Structured polarized light microscopy for collagen fiber structure and orientation quantification in thick ocular tissues

“…Polarized light microscopy (PLM) has recently been demonstrated to be a powerful and robust technique for measuring properties of collagen fibers in ocular tissues, allowing the visualization and analysis of collagen fiber anisotropy, 8 orientation, 9,10 and of microstructural crimp in the posterior pole 11 and around the globe in sheep 12 and in humans. 13 Our implementations of PLM, however, require sectioning the tissue for imaging using transmitted light, usually after fixation. This is slow, destructive, and limits the analysis to thin sections.…”