Corneal Nerve Plexus - AK Khurana (Comprehensive Ophthalmology)

Nerve Supply of the Cornea

"Cornea is supplied by anterior ciliary nerves which are branches of the ophthalmic division of the 5th cranial nerve (trigeminal nerve). After going about 2 mm in cornea, the nerves lose their myelin sheath and divide dichotomously and form three plexuses:

1. Stromal plexus
2. Subepithelial plexus
3. Intraepithelial plexus"

The Three Plexuses in Detail

• Located within the corneal stroma
• Formed by myelinated nerve trunks entering the cornea radially from the limbus
• Nerves lose their myelin sheath approximately 2 mm after entering the cornea
• Branches divide dichotomously (repeatedly splitting into two)
• Acts as the primary nerve network within the stromal tissue

• Located just beneath the corneal epithelium, above Bowman's layer
• Formed by terminal branches of stromal nerves that penetrate Bowman's layer
• This is the plexus visible on in vivo confocal microscopy (IVCM)
• Contains both Aδ (thinly myelinated, fast pain) and C fibers (unmyelinated, slow pain/thermal)
• Forms a characteristic whorl-like (vortex) pattern approximately 1-2.5 mm inferonasal to the corneal apex

• Terminal nerve endings running between and within epithelial cells
• Free nerve endings - responsible for the cornea's extreme pain sensitivity
• These are the sensory receptors for pain, touch, and temperature

Key Facts (from Kanski's + Khurana)

Clinical Significance

• Corneal reflex (blink reflex): Afferent limb via V1 (trigeminal); efferent via CN VII (facial nerve). Touching the cornea produces reflex bilateral lid closure. - Kanski's Clinical Ophthalmology, 10th ed.
• Pain and photophobia: Abrasion, bullous keratopathy, and elevated IOP (as in congenital glaucoma) cause intense pain, photophobia, and reflex lacrimation due to stimulation of corneal free nerve endings.
• Neurotrophic keratitis: Damage to corneal nerves (e.g., herpes simplex, acoustic neuroma surgery, trigeminal nerve lesions) leads to loss of corneal sensation, impaired epithelial healing, and risk of ulceration.
• Confocal microscopy: The subbasal plexus is the standard target for assessing peripheral neuropathy (e.g., diabetic neuropathy) non-invasively. Reduced nerve fiber density and branching correlate with disease severity.
• Post-LASIK/PRK/CXL: Subbasal plexus is disrupted by these procedures; regeneration takes months to years, explaining post-surgical dry eye and reduced sensation.

Whorl Pattern of the Sub-basal Plexus

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