Quantitative structural imaging of keratoconic corneas using polarization-resolved SHG microscopy

Area of Science:

• Biomedical Optics
• Ophthalmology
• Materials Science

Background:

• The human cornea's structural integrity relies on aligned collagen fibrils within lamellae.
• Keratoconus is a progressive corneal disease characterized by thinning and steepening, impacting collagen organization.
• Understanding corneal microstructure is crucial for diagnosing and managing pathologies.

Purpose of the Study:

• To employ polarization-resolved second harmonic generation (P-SHG) microscopy for characterizing collagen structure in healthy and keratoconic human corneas.
• To quantitatively assess collagen lamellar organization across the full corneal thickness.
• To evaluate P-SHG microscopy as a tool for analyzing structural defects in collagen-rich tissues.

Main Methods:

• Human corneal tissues (8 control, 6 keratoconic) were analyzed using P-SHG microscopy.
• Automated image processing provided sub-micrometer resolution collagen orientation mapping.
• Collagen orientation distribution was quantitatively analyzed using entropy and orientation index.

Main Results:

• Sutural lamellae in the anterior stroma showed a consistent inclination (22° ± 5°) in both control and keratoconic corneas.
• A significant loss of collagen order and lamellar disorganization was observed in keratoconic corneas throughout the full stromal thickness.
• Quantitative analysis revealed significant differences in entropy and orientation index between control and keratoconic corneas.

Conclusions:

• P-SHG microscopy effectively detects and quantifies collagen structural defects in keratoconus.
• Corneal lamellar disorganization, detectable by P-SHG, correlates with the known mechanical deficits in keratoconus.
• P-SHG microscopy is a promising tool for the quantitative analysis of structural abnormalities in human corneas and other collagenous tissues.