Brainstem II: Eye Movements and Pupillary Control

Eye Movement Disorders

Indicators of brainstem or cranial nerve pathology.

Nuclear Pathways

Involve cranial nerve nuclei for eye movement.

Infranuclear Pathways

Peripheral nerves controlling extraocular muscles.

Cranial Nerves III, IV, VI

Nerves responsible for eye movement coordination.

Extraocular Muscles

Muscles that move the eyes within the orbit.

Supranuclear pathways

Brainstem and forebrain circuits controlling eye movements.

CN III, IV, VI nuclei

Cranial nerves controlling extraocular muscle movements.

Extraocular muscles

Six muscles responsible for eye movement.

Lateral rectus

Muscle responsible for lateral eye movement.

Medial rectus

Muscle responsible for medial eye movement.

Superior rectus

Muscle responsible for elevation and intorsion.

Inferior rectus

Muscle responsible for depression and extorsion.

Superior oblique

Muscle producing intorsion and depression.

Inferior oblique

Muscle producing extorsion and elevation.

Common tendinous ring

Origin point for extraocular muscles in orbit.

Eye adduction

Movement of the eye towards the nose.

Eye abduction

Movement of the eye away from the nose.

Innervation of extraocular muscles

CN VI for lateral rectus, CN IV for superior oblique, CN III for others.

Oculomotor nerve (CN III)

Innervates most extraocular muscles and eyelid elevation.

Trochlear nerve (CN IV)

Innervates superior oblique muscle for intorsion.

Abducens nerve (CN VI)

Innervates lateral rectus muscle for abduction.

Cavernous sinus

Cranial cavity location for CN III, IV, VI passage.

Diplopia

Double vision caused by muscle or nerve abnormalities.

Dysconjugate gaze

Misalignment of eyes leading to diplopia.

Amblyopia

Decreased vision in one eye due to suppression.

Oculomotor palsy

Loss of function in muscles innervated by CN III.

Head position compensations

Head turns towards affected muscle's action direction.

Parasympathetic fibers in CN III

Control pupillary constriction and lens accommodation.

Ciliary muscles

Muscles controlling lens shape for focusing.

PComm aneurysms

Can compress CN III parasympathetic fibers.

ICP

Increased intracranial pressure affecting CN VI.

Facial colliculus

Formed by CN VII fibers looping around CN VI.

Orbital myositis

Inflammation of extraocular muscles causing diplopia.

Medial Rectus

Muscle affected in oculomotor palsy.

Oculomotor Palsy

CN III dysfunction causing eye movement issues.

PComm Aneurysm

Common cause of painful CN III palsy.

Trochlear Palsy

CN IV dysfunction causing vertical diplopia.

Hypertropia

Eye resting in elevated position due to CN IV.

Abducens Palsy

CN VI dysfunction leading to horizontal diplopia.

Lateral Rectus

Muscle responsible for eye abduction.

Head Rotation

Compensatory movement toward affected eye.

Pupillary Light Reflex

Contraction of pupils in response to light.

CN II

Optic nerve involved in light reflex.

Edinger-Westphal Nuclei

Location of preganglionic parasympathetic fibers.

Ciliary Ganglia

Synapse site for parasympathetic fibers in orbit.

Ciliary Muscle

Adjusts lens thickness for focusing images.

Sympathetic Pathway

Controls pupillary dilation via autonomic nuclei.

Superior Cervical Ganglion

Synapse point for postganglionic sympathetic fibers.

Anisocoria

Pupillary asymmetry; can indicate lesions.

Blown Pupil

Large pupil due to complete CN III lesion.

Vertical Diplopia

Double vision in vertical plane from CN IV.

Horizontal Diplopia

Double vision in horizontal plane from CN VI.

Infarct of Nucleus

Can cause oculomotor nerve dysfunction.

Herniation of Temporal Lobe

Can compress CN III, causing palsy.

Microvascular Damage

Common cause of CN palsies in diabetes.

Pontine Infarcts

Can damage CN VI fascicles, affecting gaze.

Consensual Response

Pupillary constriction in both eyes from light.

Pupillary Dilator Muscle

Muscle responsible for pupil dilation.

Blown pupil

Pupil remains dilated due to parasympathetic loss.

Ptosis

Drooping of the upper eyelid.

Horner's syndrome

Condition causing ptosis, miosis, and anhidrosis.

Miosis

Constricted pupil size.

Anhidrosis

Decreased sweating in face and neck.

CN III palsy

Weakness affecting levator palpebrae superior.

Myasthenia gravis

Autoimmune disorder causing muscle weakness.

Blepharoplasty

Surgical procedure to correct eyelid drooping.

Medial longitudinal fasciculus (MLF)

Coordinates eye movements via CN nuclei.

Paramedian pontine reticular formation (PPRF)

Center for horizontal gaze control.

Saccades

Quick eye movements between objects.

Smooth pursuit

Stable viewing of moving objects.

Vergence movements

Eyes move toward or away from midline.

Vestibulo-Ocular Reflex (VOR)

Stabilizes vision during head movements.

Nystagmus

Slow eye movement interrupted by fast movement.

Frontal Eye Fields

Cortical area controlling contralateral eye movements.

Vertical eye movements

Controlled by superior and inferior recti.

Horizontal eye movements

Coordinated by CN III, IV, VI nuclei.

Convergence

Eyes move inward to focus on near objects.

Divergence

Eyes move outward to focus on distant objects.

Upper midbrain reticular formation

Center for vertical eye movement control.

Cortical control

Influences eye movements via visual inputs.