Trochlear nerve 4 ( IV )

• Anatomy and Function

Origin: Dorsal midbrain

Unique features:

Smallest cranial nerve

Only cranial nerve exiting dorsally

Longest intracranial course

Innervation: Superior oblique muscle

Function: Intorsion, depression, and abduction of the eye

• Clinical Presentation of CN IV Palsy

Vertical diplopia, worse on contralateral gaze and ipsilateral head tilt

Hypertropia of affected eye, increasing on contralateral gaze and ipsilateral head tilt

Compensatory head tilt away from affected side

Excyclotorsion of affected eye

• Orthoptic Assessment

Cover test in nine positions of gaze

Measurement of vertical deviation in primary position and on head tilt

Three-step test (Parks-Bielschowsky)

Double Maddox rod test for torsion

Diplopia charting

• Etiology

Congenital (most common unilateral palsy)

Traumatic (most common acquired cause)

Microvascular ischemia

Compression (e.g., tumors, aneurysms)

• Management

Acute: Monocular occlusion or prism therapy

Chronic: Prism correction or strabismus surgery

Orthoptic exercises for improving fusional amplitudes

• Conclusion

Orthoptists play a vital role in diagnosing and managing trochlear nerve palsies. Their expertise in detailed motility assessment and understanding of CN IV function is crucial for effective patient care.

Note : This document serves educational purposes exclusively and does not constitute medical advice or treatment guidelines