- Free nerve endings of Aδ and C-fibres detect painful or noxious stimuli
- These are nerve endings of the frontal, lachrymal and nasociliary nerves
- The nasociliary nerve supplies sensation to the cornea, perilimbal conjunctiva and supero-nasal peripheral conjunctiva
- It also supplies the long and short ciliary nerves
- The lacrimal and frontal nerves supply sensation to the remaining peripheral conjunctiva
- These three musketeers pass through the superior orbital fissure
- They unite to form the ophthalmic division (V1) of the trigeminal nerve
- The cell bodies of these neurons lie within the semi-lunar (trigeminal) ganglion
- They project to the pons before ultimately terminating in the sensory trigeminal nuclei
Neural pathways of the eyes
Neural pathways of the eyes
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- The nerves supplying motor functions enter via the superior orbital fissure
- Oculomotor nerve (CN III)
- Supplies the medial, inferior and superior rectus muscles
- Supplies the inferior oblique muscle
- Trochlear nerve (CN IV)
- Supplies the superior oblique muscle (SO4)
- Abducens nerve (CN VI)
- Supplies the lateral rectus muscle (LR6)
- Inhibition of the motor components of these nerves provides akinesis of the globe
- Intra-conal injection may spare the trochlear nerve (which follows an extra-conal path) leading to inadequate akinesis of superior oblique
- The optic nerve leaves the globe postero-medially
- It passes through the orbit and exits via the optic foramen
- It is vulnerable to injury e.g. during retrobulbar block with an overly-long needle or if the patient looks supero-nasally