Sclera, Limbus & Clinical Correlations

Sclera, Limbus & Clinical Correlations

High-Yield Clinical + PYQ Focus

Sclera Overview

• Forms posterior 5/6th of eyeball

• White appearance → irregular collagen fibers

• Protective + structural role

• Non-elastic (unlike cornea)

Thickness Variation

Thinnest: behind recti insertion (0.4 mm)

Thickest: around optic nerve (1 mm)

Limbus: ≈ 0.83 mm

Average: 0.6-0.8 mm

Layers of Sclera

  • Episclera → highly vascular (superficial + deep)
  • Sclera proper → avascular (main bulk)
  • Lamina fusca → innermost pigmented layer

Episclera Details

• Highly vascular (2 plexuses)

• Merges with Tenon’s capsule

• Located ~3 mm posterior to limbus

• Inflammation here → blanches with phenylephrine

CORNEA SCLERA OPTIC NERVE LIMBUS

Scleritis

• Deep vascular inflammation

• Bluish/violet hue (characteristic)

• Severe pain (can wake at night)

• Vessels DO NOT blanch with drops

• Associated with systemic disease (40-50%)

Episcleritis

• Superficial inflammation

• Idiopathic (most common, 90%)

• Mild pain / Foreign body sensation

• Vessels blanch with phenylephrine

• Self-limited (2-3 weeks typically)

Types of Scleritis

  • Non-necrotizing (anterior/posterior)
  • Necrotizing with inflammation (painful)
  • Scleromalacia perforans (painless, worst prognosis)

Necrotizing types → higher systemic disease risk

Vasoconstrictor Test

Drug: Phenylephrine 2.5%

✔ Episcleritis: redness disappears

✖ Scleritis: redness persists

Gold standard clinical test

Scleritis

Deep inflammation • Painful • No blanching

Episcleritis

Superficial • Mild pain • Blanches with drops

Key Difference

Depth of inflammation • Vascular response

🔬 Limbus (Very Important)

Corneo-scleral junction where magic happens!

📍 Contains: Limbal stem cells (regenerate corneal epithelium)

🧬 Markers:

CD34 → universal marker
ABCG2 → specific marker

Location: Palisades of Vogt (radial ridges)

✨ Function: Prevents keratinization, maintains corneal clarity

⚠️ PYQ Alert Box

✔ Episcleritis → redness blanches with phenylephrine

✖ Scleritis → redness DOES NOT blanch

✔ Limbus → contains regenerative stem cells

✖ Scleromalacia → painless but destructive (necrotizing)

🎯 Rule: Scleritis pain severity > Episcleritis always

🎯 Exam Trap & Link

Common Mistakes:

• Scleritis ≠ superficial

• Episcleritis ≠ severe pain

Clinical: Limbal stem cell deficiency → Pterygium | Treatment: Limbal graft

Scroll to Top