3rd nerve palsy

 

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 nerve supply	Normal function	In the case of oculomotor nerve palsy
SR, MR, IR, IO (except SO & LR)	Move the eye upwards, medially	SO & LR muscles still work, they pull the eye downward and outward, causing it to rest in a ‘down and out’ position.
LPS	Raises the upper eyelid	Ptosis
Sphincter pupillae muscle	Constricts the pupil (Miosis)	Mydriasis (dilated pupil)
Ciliary muscle	Controls lens shape for focusing	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