Characterization of lamina cribrosa beam insertion into the sclera canal in sheep, pig, monkey, and human

Abstract

Purpose : The interactions between the sclera and lamina cribrosa (LC) are primarily through the LC beam insertions. Thus, the LC insertions are important to determine how/whether the sclera provides mechanical support to the LC. Our goal was to characterize the LC insertion width and shape in human, monkey, pig, and sheep eyes.

Methods : Three coronal optic nerve head (ONH) cryosections through the LC were collected from each of the four species, and imaged using polarized light microscopy (PLM). We then measured manually the width of all insertions, noting their region (inferior/superior, I/S or nasal/temporal, N/T). Differences in insertion width between species and between regions within each species were analyzed by t-tests.

Results : LC beam insertions into the sclera varied in shape (curved or straight), width (broad or narrow), and penetration depth (shallow or deep) (Fig 1). Insertion widths were significantly different between all species (p<0.001): with widths (mean±SD) in human 55.28±27.07μm, sheep 98.18±56.45μm, pig 137.02±79.91μm and monkey 25.95±14.98μm (Fig 2). Pig and sheep tended to have more curved insertions than primates. No significant regional difference (I/S vs N/T) in width was detected.

Conclusions : LC insertions vary substantially from one another, and significantly between species. These differences may influence the mechanical robustness of this critical region of the LC. For example, a wider LC insertion may allow thin beams to support similar IOP-induced forces as thicker beams, providing stronger support to neural tissues. Understanding LC insertions may help figure out why peripheral vision is affected earlier in glaucoma.

This is a 2020 ARVO Annual Meeting abstract.

 

Example PLM images of human LC. Colors indicate local fiber orientation. Whole canal (a) and close-ups of insertions (b-e). Some insertions run deep into the sclera (c), sometimes very deep (b). Insertions were sometimes narrow and straight into the canal (d), or curved that seemed to integrate into the circumferential ring.

 

LC insertion widths were substantially and significantly different between all species (p<0.001).