Corneal and scleral collagens--a microscopist's perspective

Area of Science:

• Ophthalmology
• Biophysics
• Materials Science

Background:

• The corneal and scleral stroma's structural organization is crucial for ocular function.
• Collagen fibrils are the primary structural components of these tissues.
• Understanding collagen distribution and organization is key to comprehending stromal biomechanics and optical properties.

Purpose of the Study:

• To review the microscopical techniques used to study collagen distribution and organization in the cornea and sclera.
• To highlight the contributions of various microscopy methods to our understanding of stromal structure.
• To correlate collagen organization with tissue function, particularly corneal transparency.

Main Methods:

• Review of studies employing light microscopy (polarized, confocal, immunolabeling), electron microscopy (scanning, transmission, cryo-etching, rotary shadowing), and atomic force microscopy.
• Analysis of findings related to collagen fibril diameter, packing, orientation, and interactions with proteoglycans.

Main Results:

• Light microscopy revealed the lamellar structure and fibril orientation.
• Electron microscopy demonstrated differences in corneal (regular) and scleral (irregular) collagen fibril diameters, informing theories of corneal transparency.
• Advanced microscopy identified the role of proteoglycans in collagen organization and type V collagen in regulating fibril diameter.
• Atomic force microscopy confirmed previous findings on fibril organization and cross-bridge structures.

Conclusions:

• Microscopy techniques have progressively elucidated the intricate collagen organization within the cornea and sclera.
• The uniformity of collagen fibrils in the cornea is essential for its transparency.
• Proteoglycans and specific collagen types play critical roles in maintaining stromal architecture and function.