Collagen Crimp Period in the Corneoscleral Shell

Abstract

 

Purpose

 

The mechanical properties of the corneo-scleral shell are central to the physiology and pathophysiology of the eye. These properties are largely determined by the architecture of their constitutive collagen fibers, and in particular the collagen fiber crimp period. Our goal was to measure the distribution of collagen fiber crimp period of the corneo-scleral shell from the apex of the cornea to the optic nerve head (ONH).

 

Methods

 

A sheep eye (<2 yo) was obtained from a local slaughterhouse and fixed overnight in formalin (10%) within 24 hours of death. Following fixation, the eye was cryosectioned axially (35 µm). Five consecutive sections were selected for analysis, starting with the one passing through the central cornea and ONH and progressing superiorly into the peripapillary sclera (PPS). Sections were imaged using light microscopy (Olympus BX60, 12bit gray-scale, 10x, NA 0.30, 0.73µm/pixel). The crimp period (averaged over 3 consecutive periods) was manually measured in 17 regions (Fig1) with at least 20 measurements per region. A matrix of two-sample t-tests were done to see which regions were significantly different from one another (P<0.001) (Fig2B).

 

Results

 

Collagen crimp period varied substantially over the globe (Figure 2A), being smallest in the cornea (mean±SD) 17±5.3µm and PPS 23±9.3µm regions, and increasing with distance from these two areas. Within the cornea, the nasal cornea crimp period was significantly different from the central and temporal cornea and within the PPS, the temporal PPS was significantly different from the superior PPS (Fig2B).

 

Conclusions

 

There were substantial and significant differences in collagen crimp period across the corneoscleral shell. Collagen fiber crimp period was lowest at the poles and twice as large near the equator. The biomechanical consequences and role of these variations are still unclear and should be further investigated.

 

 

FIGURE 1: Axial sections of a sheep eye were quantified in 17 regions.

 

 

FIGURE 2: A) Crimp period measurements in the corneoscleral shell. The line connects the mean crimp period per region. B) We evaluated whether the crimp periods between regions were significantly different. The results for cornea and PPS are shown. Regions that were different are marked with a star and red coloring, whereas those that were not different are green.

 

Keywords: 708 sclera • 598 microscopy: fixation processing • 599 microscopy: light/fluorescence/immunohistochemistry