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.

 

 

Licence- Creative CommonsnSource- https://flic.kr/p/TsppAdnAuthor- FlickrFigure- Left-sided ptosis from 3rd nerve palsy

 

 

 

 

Reference:

1. Comprehensive ophthalmology, A K Khurana, 7th edition, P. No. 369

 


 

 

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