Opthalmoplegia: weakness or paralysis of one or more extraocular muscles responsible for eye movements. Two types: internuclear vs external.
1. Causes of opthalmoplegia:
Internuclear: Traumatic, or neurological causes such as:
- Multiple sclerosis: Demyelinating disorder, often affects bilaterally
- Cranial nerves: Oculomotor, trochlear, abducens
- Foville’s Syndrome: Brainstem stroke
- Parinaud’s Syndrome: Dorsal midbrain
- Frontal eye fields: Intersection of precentral and middle frontal gyrus.
External: Muscular or mitochondrial disorders such as:
- Graves disease: Graves’ opthalmopathy associated with various signs.
- Kearns-Sayre Syndrome: Mitochondrial disease characterized by progressive external opthlamoplegia (PEO), pigmentary retinitis and onset before 20 years-old. Common additional S/S: Deafness, cerebellar ataxia, heart block.
- Toxic envenomation: mambas, taipans, kraits
- Thiamine deficiency: Wernicke’s encephalopathy
- Lyme disease: Borrelia burgdorferi: causes not only uveitis, but also keratitis, iridocyclitis, vitritis, multifocal choroiditis, exudative retinal detachment and panophthalmitis.
2. Central lesions affecting horizontal gaze:
In order for both eyes to look at the same side, central lesions usually affect at least one of the following sites:
- Contralateral frontal eye field
- Ipsilateral PPRF
- Ipsilateral abducens nucleus
- Contralateral MLF
- Contralateral oculomotor nucleus
Note that the oculomotor nucleus is in the midbrain, and PPRF and abducens nucleus sits in the pons, with the abducens nucleus near the bottom. Also note MLF is not a nucleus but rather a fasciculus that connects not only the oculomotor and abducens, but also trochlear and vestibular nuclei.
Pathway is as follows: Say you want to make both eyes look LEFT. Signal starts from the RIGHT frontal eye field to the left PPRF, and goes to the left abducens nucleus. There the abducens nucleus sends a signal both to the lateral rectus of the left eye telling it to abduct and to the right oculomotor nucleus which causes the medial rectus of the right eye to adduct.
- Frontal eye field: contralateral bilateral gaze palsy
- PPRF and Abducens nucleus: Ipsilateral bilateral gaze palsy (PPRF: saccades, Abducens nucleus: saccades+VOR vestibule-ocular reflex)
- MLF (INO) : Contralateral gaze palsy with contralateral nystagmus.
- One and a Half Syndrome: One sided MLF and Abducens nucleus causes ipsilateral bilateral gaze palsy AND contralateral gaze palsy with contralateral nystagmus.
- Oculomotor opthalmoplegia: Ipsilateral adduction palsy.
- Foville’s Syndrome: (Posterior INO) Ipsilateral bilateral gaze palsy (conjugate gaze palsy, contralateral limb paralysis, and ipsilateral facial paralysis.
- WEBINO syndrome: Wall Eyed Bilateral INO: rostral lesion within the midbrain, may cause bilateral divergence.
3. Central lesions affecting vertical gaze:
Upward vertical gaze palsy: Parinaud’s syndrome (Dorsal midbrain syndrome)
Lesion in the rostral midbrain (near oculomotor nucleus and pretectal area) (pineal tumors) causes paralysis of vertical gaze and failure of convergence, but retention of normal lateral gaze. Affects all vertical eye movements including saccades. Patient has: Sunset Eyes Sign, Collier Sign (bilateral lid retraction), large, irregular pupils that do not react to light but may react to near-far accommodation. Doll’s head maneuver should elevate the eyes, but eventually all upward gaze mechanisms fail.
Downward gaze palsies: progressive supranuclear palsy, lesions of rostral interstitial nucleus of the MLF (riMLF). Normally has bilateral effects on elevator muscles: superior rectus and inferior oblique muscles; as well as depressor muscles: inferior rectus and oblique muscles, thereore lesions to the riMLF has more effect on downward than upward saccades.
Bonus: Locked-in syndrome: Often caused by pontine lesions, if large can disrupt bilateral corticospinal tracts and abducens nuclei, eliminating body movements and horizontal eye movements. Sometimes vertical eye movements are preserved.
4. Optic radiation, Baum’s vs Meyer’s Loop:
From the inferior retina, also called Archambault’s loop. Passes thru the temporal lobe by looping around the inferior horn of the lateral ventricle. Carries info of superior part of visual field. (Causes Pie in the sky defect of contralateral side).
From superior retina, travels straight back thru parietal lobe to occipital lobe in retrolenticular limb of internal capsule to visual cortex. Carries info from inferior part of visual field. Takes a shorter path, are less susceptible to damage. (Causes Pie in the floor defect of contralateral side).
5. Location of visual cortices:
Visual cortex receives radiation from lateral geniculate nucleus in the thalamus. Blood supply from calcarine branch of posterior cerebral artery.
Pathways and locations associated with continued visual pursuit of an object: