Scleral structure, organisation and disease. A review.

Area of Science:

• Ophthalmology
• Connective Tissue Biology
• Immunology

Background:

• The sclera, a dense collagenous layer, provides structural integrity and protection to the eye.
• Its unique organization and viscoelastic properties are crucial for maintaining vision stability.
• The sclera's avascular nature and specialized structures like the trabecular meshwork and lamina cribrosa are key to its function.

Purpose of the Study:

• To detail the microscopic structure and composition of the sclera.
• To explain the sclera's role in maintaining ocular stability and visual function.
• To explore the pathogenesis and potential autoimmune etiology of scleritis, a severe inflammatory disease of the sclera.

Main Methods:

• Histological examination of scleral layers and extracellular matrix components.
• Analysis of collagen types, proteoglycans, and elastic fibers within the sclera.
• Review of inflammatory processes and cellular infiltration in scleritis, including immune cell involvement.

Main Results:

• The sclera comprises distinct layers (Tenon's capsule, episclera, stroma, lamina fusca) with specialized regions.
• Collagen types I and III, proteoglycans (decorin, biglycan, aggrecan), and elastic fibers constitute the scleral matrix.
• Scleritis involves fibroblastic changes and infiltration by macrophages and T-lymphocytes, resembling systemic autoimmune connective tissue diseases.

Conclusions:

• Scleral structure and composition are essential for stable vision.
• Inflammatory conditions like scleritis can lead to rapid vision loss and scleral destruction.
• An autoimmune mechanism is strongly suggested for scleritis, though initial triggers remain under investigation.