The subfibrillar arrangement of corneal and scleral collagen fibrils as revealed by scanning electron and atomic force microscopy

The present study was designed to analyze the subfibrillar structure of cor neal and scleral collagen fibrils by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Isolated collagen fibrils of the bovine cor nea and sclera were fixed with 1% OsO4, stained with phosphotungstic acid a nd uranyl acetate, dehydrated in ethanol, critical point-dried, metal-coate d, and observed in an in-lens type field emission SEM. Some isolated collag en fibrils were fixed with 1% OsO4, dehydrated, critical point-dried and ob served without metal-coating in an AFM. Isolated collagen fibrils treated w ith acetic acid were also examined by SEM and AFM. SEM and AIM images revea led that corneal and scleral collagen fibrils had periodic transverse groov es and ridges on their surface; the periodicity (i. e., D-periodicity) was about 63 nm in the cornea and about 67 nm in the sclera. Both corneal and s cleral collagen fibrils contained subfibrils running helicoidally in a righ tward direction to the longitudinal axis of the fibril; the inclination ang le was about 15 degrees in the corneal fibrils and 5 degrees in the scleral fibrils. These findings indicate that the different D-periodicity between corneal and scleral fibrils depends on the different inclinations of the su bfibrils in each fibril. The present study thus showed that corneal collage n fibrils differ from scleral collagen fibrils not only in diameter but als o in substructure.