Cornea

The Cornea

Professor of Ophthalmology Dr. Amani Badawi

• Cornea case

Gross Anatomy

• Anterior 1/6 of outer coat

• Transparent & No BVs

• Diameter:

  • Horizontal 12 mm
  • Vertical 11 mm

• Thickness:

  • Central 0.5 - 0.6 mm
  • Peripheral 0.8 - 1.0 mm

• Refractive Power: 42 D

• What is The LIMBUS?)

Vertical Corneal Diameter 11.7 mm Horizontal Corneal Diameter 11 mm

Minute Anatomy

6 LAYERS

1. Epithelium

   • St. Squamous Nonkeratinised
   • (5-6 layers), 50 microns

2. Bowman’s layer

   • Structureless (Acellular) condensation
   • Never regenerate

3. The Stroma - 90% of corneal thickness - C T Bundles (Regular arrangement) - 500 microns thick

4. Descemet’s Membrane

   • Homogenous, Structureless & Highly Elastic
   • Resistant & Easily Regenerate
   • 5 microns thick in children and 15 microns thick in older adults.

5. Corneal Endothelium

• One Layer of Polyhedral cells
• Partial dehydration of the cornea
• Continuous with the Endothelium Trabecular meshwork (T M).
• About 5 microns.

6. Dua Layer (Newly Discovered) Z

• Discoverer by Harminder Dua 2013.
• Strong layer between the corneal stroma and Descemet’s membrane
  • 15 microns thick

Nerve Supply of the Cornea 5th C.N

Corneal Physiology

NUTRITION (cornea is avascular)

• By diffusion
  • Tear Film
  • Aqueous humour
  • Limbal capillaries

CORNEAL TRANSPARENCY (WHY)

Anatomical Factors:

• Cornea is avascular
• Stromal lamellae are regular
• Nerves are nonmyelinated
• Precorneal tear film

Physiological Factors:

• Corneal dehydration
• Uniform refractive indices of corneal tissue

FUNCTIONS OF THE CORNEA

• Refractive 42 D
• Protective (corneal reflex)

The Limbus (The Corneo-Scleral Junction)

• Corneal epithelium → Conjunctival epithelium
• Bowman’s membrane ends as a rounded border
• Stroma → Sclera (irregular lamellae)
• Descemet’s membrane → Trabecular meshwork
• Endothelium → Endothelium of the angle of AC

Corneal Diseases

Keratitis

• KERATOS

  • Cornea

• iTiS

  • Inflammation

• Superficial keratitis

  • Suppurative (Corneal Ulcer)
  • Non Suppurative (Pannus)

• Interstitial keratitis

• Deep keratitis

Corneal Ulcers

Primary Corneal Ulcers

• Infected Corneal ulcer

  • Hypopyon Ulcers (Bacterial)
  • Herpetic Ulcers (Viral)
  • Mycotic Ulcers (Fungal)
  • Acanthamoeba Keratitis (Protozoa)

• Non-Infected Corneal ulcer

Secondary Corneal Ulcers

• Keratomalacia
• Atheromatous Ulcer
• Ulcer with Lagophthalmos
• Neuroparalytic Ulcer
• Traumatic Ulcer

Degenerative Conditions

• Arcus Senilis
• Band Shaped Keratopathy
• Keratoconus

Management

• Keratoplasty

Quiz 1

Put “True” or “False” in the following statement:

About Hutchinson’s rule;

1. Hutchinson’s rule signifies increased risk of conjunctivitis & keratitis.

2. Hutchinson’s rule signifies increased risk of Uvietis

3. Vesicles on the tip of the nose, because the frontal branch of the trigeminal nerve.

4. Provisional diagnosis of Herpes simplex Ophthalmicus.

Quiz 2

Give differences between bacterial and fungal corneal ulcers.

Z local general predisposing #Z most common side effect glacoma from topical steroids or increased intraocular pressure PPLV Corneal Ulcer Z FT Z to confirm diagnosis

3 months boy suffering from wide pupil in left eye