Evolution of the vertebrate corneal stroma

Area of Science:

• Ophthalmology
• Biophysics
• Evolutionary Biology

Background:

• The cornea is the eye's primary refractive component, but the mechanisms governing its shape and visual acuity are not fully understood.
• Collagen's role in corneal structure and function is critical, yet its evolutionary changes are not well-characterized.

Purpose of the Study:

• To investigate the evolutionary and structural changes in corneal stromal collagen architecture across different vertebrate groups.
• To correlate collagen organization with tissue stiffness and its potential impact on corneal shape.

Main Methods:

• Utilized multiphoton, non-linear optical microscopy to image collagen using second harmonic generated signals (SHG).
• Analyzed collagen architecture in the corneal stroma of various vertebrates, from fish to mammals.

Main Results:

• Observed a progression in collagen organization complexity from lower to higher vertebrates.
• Fish and amphibians exhibit plywood-like orthogonal collagen sheets; reptiles show broader, anastomosing lamellae.
• Birds display a complex 'chicken wire' pattern, while mammals have a random lamellar pattern, particularly in the anterior stroma, correlating with increased stiffness.

Conclusions:

• Corneal collagen organization significantly evolves across vertebrate species, influencing tissue mechanical properties.
• The increasing complexity of collagen architecture is linked to enhanced corneal stiffness, potentially optimizing visual acuity in higher vertebrates.