CN III, IV and VI

Anatomy And Physiology

The oculomotor (third), trochlear (fourth), and abducens (sixth) cranial nerves control the movements of the upper eyelid, eyeball, and pupils.
They help in finding, fixating, focusing, and following a visual target.
The medial rectus is supplied by the third nerve and adducts the eye.
The lateral rectus is supplied by the sixth nerve and abducts the eye.
The superior rectus is supplied by the third nerve and elevates, adducts, and intorts the eye.
The inferior rectus is supplied by the third nerve and depresses, adducts, and extorts the eye.
The superior oblique is supplied by the fourth nerve and depresses, abducts, and intorts the eye.
The inferior oblique is supplied by the third nerve and elevates, abducts, and extorts the eye.
The levator palpebrae superioris is supplied by the third nerve and elevates the upper eyelid.
The constrictor pupillae and ciliary muscles are supplied by the third nerve and constrict the pupils.

Elicit a history of drooping of the eyelids (ptosis).
Ask about misalignment of the eyes or squint.
Inquire if the child complains of double vision (diplopia).
Elicit a history of difficulty in following fast-moving objects.
Ask about an altered size of the pupils.
Inquire about recent infections, fever, trauma, or signs of raised intracranial pressure like headache and vomiting.

Observe the eyes in the primary position of gaze.
Look for drooping of the upper eyelids (ptosis).
Check the margin-reflex distance by comparing the distance between the lid margin and the corneal light reflection.
Note the position of the eyeballs for enophthalmos or exophthalmos.
Look for the presence of squint (strabismus).
Observe the pupils for size, shape, equality, and symmetry in dim ambient light.
Look for rhythmic involuntary oscillatory movements of the eyes (nystagmus).

Palpation is not directly applicable for assessing the cranial nerves three, four, and six.

Fix the position of the head and ask the child not to move the head while moving the eyes.
Ask the child to follow a target or finger.
Move the finger to form an English letter 'H' to test all extraocular muscles.
Test each eye separately and then both eyes together.
Note any restriction of movement, diplopia, or nystagmus during the maneuver.

Perform the test in a dimly illuminated room.
Ask the child to look at a distant object to prevent the near-pupil response.
Direct light reflex: Beam a bright light into one eye from the side and observe brisk pupillary constriction in the same eye.
Consensual light reflex: Beam a bright light into one eye and observe pupillary constriction in the opposite eye.
Swinging flash light test: Swing the light rapidly between the two eyes to detect a Relative Afferent Pupillary Defect (RAPD).
Accommodation reflex: Ask the child to fixate on a distant object, then suddenly bring a finger in front of the eyes and ask the child to focus on it.
Normal accommodation response is adduction of both eyes and constriction of the pupils.

Hirschberg test: Beam a torch light into the eyes and observe the position of the corneal light reflection.
The reflection is normally at the center of the cornea.
Shift of reflection indicates manifest squint (esotropia or exotropia).
Cover test: Ask the child to look with both eyes at a target.
Cover one eye and rapidly uncover it to detect latent squint.

Diplopia on looking downwards and away from the affected side.
The child adopts a compensatory head tilt towards the opposite shoulder to eliminate vertical deviation.

Doll's eye phenomenon (oculocephalic reflex) is used to test eye movements in infants up to ten days of life or comatose children.
Turn the head rapidly from side to side; normally, the eyes lag behind and move in the opposite direction.
Presence of Doll's eye movements indicates an intact brainstem.
Oculomotor apraxia can be tested by flickering fingers on the sides to elicit saccadic pursuit movements.
Visual fields in infants are assessed roughly by introducing bright objects from behind and observing head turning or saccades.

Oculomotor, Trochlear, And Abducens Nerves Assessment:

Inspection: No ptosis noted bilaterally. Both eyeballs are centrally placed in the primary position of gaze. No evidence of enophthalmos or exophthalmos. Pupils are equal, round, and 3 mm in size bilaterally.
Extraocular Movements: Full range of extraocular movements is present in all six cardinal directions of gaze in both eyes. No restriction of abduction, adduction, elevation, or depression. No nystagmus or diplopia reported by the child.
Pupillary Reflexes: Direct and consensual pupillary light reflexes are brisk and equal bilaterally. Accommodation reflex is intact with normal convergence and pupillary constriction.
Squint Assessment: Hirschberg test reveals a central corneal light reflex symmetrically in both eyes. Cover test is negative for any latent squint.
Interpretation: Cranial nerves III (Oculomotor), IV (Trochlear), and VI (Abducens) are intact and functioning normally.