Collagen Microstructure In The Human Optic Nerve Head: Distribution And Fiber Orientation

Abstract

 

Purpose:

 

To analyse fibrillar collagen distribution and connective tissue fiber orientation within the human optic nerve head (ONH).

 

Methods:

 

Second harmonic generation (SHG) microscopy and small angle light scattering (SALS) were performed on transverse 100μm human ONH cryosections (n=10 sections, cut pre- to post-laminar in each ONH). Collagen fibril distribution and orientation were visualized in SHG datasets and preferred fiber orientation and degree of fiber alignment were mapped in 100μm steps (with SALS) across each section.

 

Results:

 

SHG scatter revealed collagen fibril bundles radially orientated, and around pores in the lamina cribrosa (LC), surrounding central retinal vessels in the prelamina and LC; circumferentially in the peripapillary sclera and longitudinally in postlaminar septae. SALS data supported fiber orientation data indicated by SHG (see Figure). Specifically, quantitative measurements of fiber organization and fiber maps from SALS identified close correlation with these observations. In the LC, the preferred fibre orientation depicted the hourglass connective tissue architecture characteristic of regional LC variation. The degree of fiber alignment was high (0.6, where 0 is random and 1 perfect alignment) in the peripapillary sclera adjacent to the LC, but low (0.2) in the region of LC insertion into the sclera. Regional collagen fibril/fiber distributions and orientation in a right eye appeared to mirror that in the left eye of the same donor. Similar findings were observed in both young and old ONHs.

 

Conclusions:

 

Fibrillar collagen distribution and fiber orientation is distinct in different regions of the human ONH. Combined SALS fiber orientation maps and SHG scatter signals allow clear interpretation of quantitative data and will aid in the characterization of ONH connective tissue architecture, a critical step to further our understanding of LC biomechanics and why some ONHs are predisposed to glaucomatous optic neuropathy.  

 

Keywords: lamina cribrosa • extracellular matrix • imaging/image analysis: non-clinical