To understand the symptoms of third nerve palsy, it is essential to know which eye muscles are supplied by the oculomotor nerve.
Oculomotor nerve (3rd cranial nerve) supplies to-
1. Somatic Motor (GSE) Fibers: innervate most of the extraocular muscles, which include:
a. Superior rectus (SR)
b. Medial rectus (MR)
c. Inferior rectus (IR)
d. Inferior oblique (IO)
e. Levator palpebrae superioris (LPS) - raises the upper eyelid
2. Visceral Motor (GVE) Fibers: These parasympathetic fibers are responsible for:
a. Innervating the sphincter pupillae muscle, which constricts the pupil
b. Innervating the ciliary muscle, which controls lens shape for focusing
Oculomotor nerve |
Normal function |
In the case of |
SR, MR, IR, IO |
Move the eye |
SO & LR muscles still work, |
LPS |
Raises the upper |
Ptosis |
Sphincter pupillae |
Constricts the pupil |
Mydriasis (dilated pupil) |
Ciliary muscle |
Controls lens shape |
Loss of accommodation |
Clinical features of 3rd nerve palsy-
Ophthalmoplegia (Eye movement Impairment):
1. Inability to move the eye upwards, medially.
2. The eye may be positioned "down and out" due to unopposed action of the lateral rectus (innervated by the 6th cranial nerve) and superior oblique (innervated by the 4th cranial nerve)
Ptosis:
1. Drooping of the upper eyelid due to paralysis of the levator palpebrae superioris (LPS) muscle.
Fixed and dilated pupil:
1. Dilated pupil due to loss of parasympathetic input to the sphincter pupillae muscle.
2. The pupil may also be unresponsive to light (non-reactive).
Accommodation problems:
1. Difficulty with near vision due to paralysis of the ciliary muscle, which impairs lens accommodation.
Diplopia (Double vision):
1. Occurs because the eyes are misaligned due to the imbalance of muscle action.
Figure- Left-sided ptosis from 3rd nerve palsy
Reference:
1. Comprehensive ophthalmology, A K Khurana, 7th edition, P. No. 369