Oculomotor nerve 3 ( III )

• Introduction

The oculomotor nerve, the third cranial nerve (CN III), is essential for eye movement and pupillary response. Understanding its anatomy and function is crucial for orthoptists in diagnosing and managing ocular motility disorders [1].

• Anatomy and Function

Nuclei and Course

- Originates from the midbrain

- Oculomotor nucleus: somatic motor fibers

- Edinger-Westphal nucleus: parasympathetic fibers

- Exits the brainstem ventrally, passes through the cavernous sinus, enters the orbit via the superior orbital fissure

Innervation

- Superior, inferior, and medial recti muscles

- Inferior oblique muscle

- Levator palpebrae superioris

- Pupillary sphincter and ciliary muscles (via parasympathetic fibers)

• Clinical Presentation of CN III Palsy

Complete Palsy

- Ptosis

- "Down and out" position of the eye

- Impaired adduction, elevation, and depression

- Dilated pupil (if parasympathetic fibers affected)

Partial Palsy

- Variable presentation depending on affected fibers

- Pupil-sparing in microvascular cases

• Orthoptic Assessment

Ocular Motility Examination

- Ductions and versions testing

- Measurement of strabismus in nine positions of gaze

Pupillary Assessment

- Pupil size and reactivity

- Relative afferent pupillary defect (RAPD) testing

Ptosis Evaluation

- Measurement of palpebral fissure height

- Assessment of levator function

Diplopia Charting

- Documentation of diplopia fields

• Etiology

Common causes include:

Microvascular ischemia (e.g., diabetes, hypertension)

Compression (e.g., aneurysm, tumor)

Trauma

Inflammatory conditions (e.g., multiple sclerosis)

• Diagnostic Approaches

- Neuroimaging (MRI, CT angiography)

- Blood tests for underlying systemic conditions

- Tensilon test to rule out myasthenia gravis

• Management Strategies

Acute Phase

- Patching for diplopia

- Referral for urgent neurological evaluation in complete palsies

Recovery Phase

- Fresnel prisms for residual deviation

- Orthoptic exercises to improve fusional amplitudes

Chronic Phase

- Consideration of strabismus surgery

- Long-term monitoring of ocular alignment and fusion

• Prognosis

Prognosis varies depending on etiology:

- Microvascular causes often resolve within 3-6 months

- Compressive lesions may require surgical intervention

- Traumatic cases have variable recovery potential

• Conclusion

Orthoptists play a crucial role in the assessment, management, and rehabilitation of patients with oculomotor nerve palsies. Their expertise in detailed motility assessment and diplopia management is essential for optimizing visual outcomes and quality of life for affected individuals.

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