Sclera

 

🧠 What Is the Sclera?

The sclera is the opaque, white outer layer of the eye that surrounds most of the eyeball (except the cornea in the front). It helps maintain the shape of the globe and offers a sturdy attachment for the extraocular muscles.

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📚 Anatomy of the Sclera:

1. Location & Extent:

   • Covers posterior five-sixths of the eyeball

   • Extends from the limbus (edge of the cornea) to the optic nerve

   • Continuous anteriorly with the cornea at the corneoscleral junction (limbus)

   • Posteriorly, it's pierced by the optic nerve and surrounded by the lamina cribrosa

2. Layers of the Sclera (from outermost to innermost):

   1. Episclera

   • Loose, vascular connective tissue

   • Lies just beneath the conjunctiva

   • Rich in blood vessels—plays a role in inflammation (episcleritis)

   2. Scleral Stroma (Proper Sclera)

   • Dense, irregular connective tissue

   • Mainly collagen and fibroblasts

   • Gives the sclera its strength and rigidity

   • Fewer cells and more irregular collagen fibers than the cornea—hence, it’s opaque

   3. Lamina Fusca

   • Innermost layer

   • Brownish in color due to pigmented cells

   • Lies adjacent to the choroid and ciliary body

   • Contains elastic fibers and is loosely arranged to allow for some flexibility

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🔌 Nerve & Blood Supply:

• Avascular centrally, but the episclera has a vascular network

• Supplied by short and long posterior ciliary arteries

• Innervated by branches of the trigeminal nerve (CN V1)

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⚙️ Functions of the Sclera:

• Protects inner eye structures

• Maintains shape of the eyeball

• Anchor point for six extraocular muscles (for eye movement)

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🧾 Clinical Notes:

• Scleritis: Painful inflammation often linked to autoimmune diseases

• Episcleritis: More benign, less painful inflammation of the outermost layer

• Blue Sclera: Seen in conditions like osteogenesis imperfecta due to thinning