Quantization of collagen organization in the stroma with a new order coefficient.

James A Germann,Eduardo Martinez-Enriquez,Susana Marcos

doi:10.1364/boe.9.000173

Abstract

Many optical and biomechanical properties of the cornea, specifically the transparency of the stroma and its stiffness, can be traced to the degree of order and direction of the constituent collagen fibers. To measure the degree of order inside the cornea, a new metric, the order coefficient, was introduced to quantify the organization of the collagen fibers from images of the stroma produced with a custom-developed second harmonic generation microscope. The order coefficient method gave a quantitative assessment of the differences in stromal collagen arrangement across the cornea depths and between untreated stroma and cross-linked stroma.

Highlights

How collagen fibers are arranged can have a huge effect on the behavior of collagenous tissue
X-ray scattering measurements revealed that collagen fibers have a preferred orientation in the stroma, with many lamellae oriented either along the superior-inferior axis or along the temporal-nasal axis except at the periphery of the posterior cornea, where they have a radial preferred orientation [2]
After treatment, corneal buttons were excised from the globes and placed on a microscope slide with a drop of buffered phosphate solution (PBS) to prevent sample dehydration, which were covered with coverslips

Summary

Introduction

How collagen fibers are arranged can have a huge effect on the behavior of collagenous tissue. The sclera of the eye is opaque, while the stroma is transparent despite both tissues being primarily composed of type I collagen fibers [1]. X-ray scattering measurements revealed that collagen fibers have a preferred orientation in the stroma, with many lamellae oriented either along the superior-inferior axis or along the temporal-nasal axis except at the periphery of the posterior cornea, where they have a radial preferred orientation [2]. Measurements in scanning electron microscopy show alternating collagen lamellae orientation along the two parallel axes in the posterior cornea, the lamellae of the anterior stroma appear to be more disorganized [3]. A competing theory on keratoconus suggests a change in the interweaving of the anterior stroma with the Bowman layer is the underlying cause [5]

Methods

Results

Conclusion