Ophthalmic Nerve
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Direct answer
Purely sensory, the ophthalmic nerve (V1) carries sensation from the eyeball, the conjunctiva, the upper lid, the dorsum of the nose, the frontal and ethmoid sinuses and the anterior dura to the trigeminal ganglion in Meckel's cave. It lies in the lateral wall of the cavernous sinus below the trochlear nerve, then divides into lacrimal, frontal and nasociliary nerves that pass through the superior orbital fissure into the orbit. Its nasociliary branch supplies the eyeball itself and gives the external nasal nerve, which is why herpes zoster vesicles on the tip of the nose warn of ocular involvement — the Hutchinson sign.
What you must remember
- In the lateral wall of the cavernous sinus the order from above downwards is oculomotor, trochlear, ophthalmic (V1) and maxillary (V2); V1 is the lowest of the three above V2.
- Of the three terminal divisions, the lacrimal and frontal nerves enter the orbit through the superior orbital fissure above the common tendinous ring, while the nasociliary passes through the ring between the two heads of the lateral rectus.
- The frontal nerve divides into supraorbital and supratrochlear nerves to the forehead and upper lid.
- The lacrimal nerve supplies the gland and receives secretomotor fibres hitch-hiking from the zygomatic nerve of V2.
- The nasociliary branch is the sensory nerve of the eyeball: its long ciliary nerves carry sympathetic dilator pupillae fibres, and the sensory root passes through the ciliary ganglion to the short ciliary nerves.
- The anterior ethmoidal nerve ends on the face as the external nasal nerve to the tip of the nose; the infratrochlear nerve supplies the side of the nose and lacrimal sac.
- V1 is the afferent limb of the corneal reflex (efferent is the facial nerve), and the only trigeminal division involved in herpes zoster ophthalmicus.
How to work through a patient with zoster ophthalmicus
A sixty-year-old presents with vesicles over the right forehead, swelling of the upper lid and — the detail that matters — a few vesicles on the tip and side of the right side of the nose. Reason through the anatomy. The virus has reactivated in the ophthalmic division; the forehead vesicles map to the supraorbital and supratrochlear branches of the frontal nerve. Vesicles on the nasal tip come from the external nasal nerve, the terminal branch of the nasociliary chain via the anterior ethmoidal nerve, and because the same parent nerve supplies the eyeball through the long and short ciliary nerves, a positive Hutchinson sign predicts corneal or uveal involvement and mandates urgent slit-lamp examination with fluorescein staining.
The same anatomy dictates the bedside tests an examiner will ask for. Touching the anaesthetised cornea tests the afferent V1 via the nasociliary; failure to blink on that side with a normal consensual blink on the other side localises the lesion to the sensory limb, while facial weakness would implicate the efferent limb. Sensory testing over the three branches — forehead, cornea, nasal tip — charts the deficit. Ongoing care per current ophthalmology practice includes topical antiviral and systemic antiviral therapy begun promptly, cycloplegia for uveitis, and monitoring for raised intraocular pressure, since nasociliary fibres also carry the sensation that makes uveitis painful.
Where students slip
The trap most frequently sprung in vivas is the superior orbital fissure: candidates state that "all three divisions pass above the annulus", forgetting that the nasociliary nerve — the one supplying the eyeball — passes within the tendinous ring alongside the oculomotor and abducent nerves, and that this is why a cavernous sinus or orbital apex lesion pairs V1 sensory loss with ocular motor palsies. The second slip is crediting the lacrimal gland's secretomotor supply to V1 itself; the parasympathetic fibres arise with the greater petrosal nerve, relay in the pterygopalatine ganglion and only join the lacrimal nerve from the zygomatic branch of V2. Finally, remember that the long ciliary nerves bypass the ciliary ganglion entirely, which is why sympathetics to the dilator pupillae survive lesions of the ganglion but not of the nasociliary nerve.
Frequently asked questions
Which branch of V1 supplies the eyeball and the tip of the nose?
The nasociliary nerve, through the long and short ciliary nerves to the globe and the external nasal branch to the nasal tip.
What does the Hutchinson sign indicate?
Vesicles on the tip of the nose in zoster ophthalmicus, showing nasociliary involvement and warning of likely ocular disease.
Which limbs of the corneal reflex travel in V1?
Only the afferent limb; the efferent blink runs through the facial nerve to orbicularis oculi.
How do the divisions of V1 enter the orbit?
The lacrimal and frontal nerves pass through the superior orbital fissure lateral to and above the common tendinous ring; the nasociliary passes through the ring itself.
Where does the ophthalmic nerve lie in the cavernous sinus?
In the lateral wall, below the trochlear nerve and above the maxillary nerve, with the internal carotid artery and abducent nerve lying medial to it within the sinus.