Matching Collagen Crimp Period Between Lamina Cribrosa and Proximal Peripapillary Sclera

Abstract

 

Purpose

 

The wavy, or crimped, collagen microstructure in the optic nerve head (ONH) largely determines the mechanical support to the retinal ganglion cell axons. Abrupt changes in this collagen crimp between lamina cribrosa (LC) and peripapillary sclera (PPS) may cause strain concentrations at the LC border, making it more susceptible to mechanical insult. We hypothesized that a proximal rim of PPS and LC will have matching collagen crimp that would render the ONH more robust.

 

Methods

 

Two sheep eyes were fixed at IOP of 0mmHg, and 2 at 10mmHg using 10%formalin. The ONHs were sectioned coronally (30µm). For each eye at least 5 sections at the level of the LC and/or PPS were imaged with light microscopy and at least 500 manual crimp period measurements were made. Linear mixed effect models were used to test whether crimp periods in the LC or PPS were associated with distance to the LC border. We also tested for differences between the LC and whole PPS as well as between LC and a proximal rim of PPS.

 

Results

 

We imaged 26 sections and made 2,746 crimp period measurements. In the LC, the crimp period was not related to distance from the LC border, whereas in the PPS, the crimp period decreased with proximity to the LC border (p<0.01, Fig 1). In all eyes the whole PPS had significantly larger crimp period than the LC (p<0.001). For every eye, we found a rim region (200-510 µm wide) for which the PPS did not have significantly different crimp period from the LC (p > 0.8). The average crimp period difference between the proximal PPS rim and LC was 0.4 µm, and their distributions had similar quartile ranges and values (Fig 2). In comparison, the average crimp period difference between the LC and the remaining PPS was 6.3 µm, and the PPS had much larger quartile ranges than the LC.

 

Conclusions

 

At low IOPs the collagen crimp period in the PPS decreased with proximity to the LC, with a proximal rim of PPS matching the LC. This crimp period arrangement in the PPS may help provide a smooth transition of biomechanical properties between tissues, reducing strain concentrations and protecting the neural tissues against insult.  

 

Fig 1. Collagen crimp period of LC (red), PPS rim (green), and remaining PPS (black) of Eye 3 (10mmHg) plotted by distance from the LC border.

 

 

Fig 2. Collagen crimp period distribution in the LC (red), PPS rim (green), and whole PPS (black).