Neuroophthalmology part 2

Dr. Sharpe

May 20, 2005

 

Light reflex

 

 

Tract goes to bilateral pretectal nuclei, thus the brain doesn’t know which eye the light is coming from.

 

RAPD – relative afferent pupullary defect

-         optic nerve disease

-         retinal disease

-         macular disease

-         chiasm lesion

-         optic tract – RAPD opposite eye

-         amblyopia if severe

-         not sean with corneal, lens, vitreous, cerebral, or functional disease

 

Simple anisocoria

        25% of population has unequal pupils >0.3mm

        Revalence increases with age

        Normal light/dark reations

        May subside or reverse within hours (see-saw anisocoria)

 

Pupilloconstrstrictor (cholinergic) dysfunction

-         damage anywhere along course of 3rd nerve

-         usually associated with other evidence of tird nerve palsy, ddx:

o       3rd nerve palsy

o       Tonic pupil

o       Pharmacological blockade

 

Review the anatomy of the 3rd nerve tract and its course.

In tentorial herniation, the temporal lobe pushes on the 3rd nerve. Thus the Hutchison pupil is the first sign of tentorial herniation (supratentorial cone)

 

3rd nerve palsy also seen in midbrain involvement, subarachnoid infiltration in meningitis, and posterior communicating artery aneurysm.

 

With recovery of the 3rd nerve palsy, redirection can cause the pupil to constrict, and also pupil size to vary with eye movement.

 

Pupil sparing 3rd nerve palsy

-         medical 3rd nerve palsy

o       atherosclerotic, hypertensive, diabetic

-         intracavernous compressive

o       meningioma, giant aneurysm

-         Genuine pupil sparing – superior division palsy

-         Apparent (pseudo) pupil sparing

o       Aberrant regeneration

o       Sympathetic palsy (coexistent, pupil doesn’t dilate well)

 

Tonic pupil – constricts to near but not to light

-         postganglionic denervation of the sphincter

-         hypersensitivity to cholinergic agents

-         can be seen in:

o       Adies syndrome – areflexic also

o       Ross syndrome – with sweating loss

o       Autonomic neuropathies, e.g., diabetes, amyloid neuropathy

-         Light reaction can be trace or segmental (if not all fibres affected)

 

In A chronic tonic pupil, the pupil is small, but still has light-near dissociation and reaction with pilocarpine. Hard to distinguish from Argyll Robertson pupil.

 

Factitious mydriasis

-         pharmacological blockade

-         pupil unusually large

-         does not react to high concentration pilocarpine

 

 

Horner’s syndrome

-         pupil small

-         mild ptosis (never below upper third of pupil), or upside down ptosis (Muller’s muscle)

-         dilated conjunctival vessels (flush) – can look like conjunctivitis – in first day

-         variable anhydrosis

-         Pupillodilator palsy

o       Lesion anywhere along sympathetic chain

o       3 anatomical segments

 

 

Ptosis can be due to

-         levator dysinsertion – senile, inflammation, contact lens, trauma

-         neuropathic – sympathetic, 34drd nerve

-         myopathic - myasthenia

-         mechanican - tumour

 

Miosis can be due to

-         Sympatheic loss

-         Simple anisocria

-         Iridocyclitis

-         Miotic eyedrops

-         Chronic tonic pupil

-         Argyll Robertson pupil

 

Pseudoptosis - pseudo-Horner’s syndrome

-         contralateral lid retraction, e.g., old Bell’s palsy

-         dermatochalasis

-         enophthalmos

-         microphthalmos

 

In Horner’s syndrome, the pupil is exacerbated in dim light. Cocaine will not dilate the pupil (blockade of NE update by cocaine normally dilates the pupil). 3rd neuron Horner’s doesn’t dilate to hydroxyamphetamine (releases NE from postganglionic ending), but does for 1st and 2nd neuron Horner’s.

 

Common causes of Horner’s

-         preganglionic brainstem infarcts

-         apical lung tumours

-         dissection of carotic artery

-         cluster headache

 

Argyll Robertson pupil

-         in syphilis

-         small pupils bilaterally

-         no light reation

-         brisk near reaction (slow in tonic pupil)

-         VDRL not adequate, need confirmatory test, e.g, FTA-Abs

-         Due to dysinhibition of the Edinger-Westphal nucleus

 

Light-near sissociation

-         Argyll Robertson pupils

-         Doral midbrain pupils

-         Tonic pupils

-         Aberrant regeneration of 3rd nerve

-         Afferent pupil defects

 

Pupils in coma

-         metabolic – small, reactive

-         tectal – large, fixed

-         diencephalic – small reactive

-         3rd nerve – dilated fixed

-         Pons – pinpoint

-         Midbrain – midposition, fixed

 

No pathological significance to hippus.

 

Oculomotor control

-         two goals

o       binocular foveation

o       prevent retinal slip

-         two modes

o       smooth movements

o       fast movements (saccades, nystagmus)

-         6 systems

o       Saccades

o       Smooth pursuit

o       Vergence

o       Vestibulo-ocular

o       optokinetic

o       fixation

 

Paramedian pontine reticular formation (PPRF) and abducens nucleus. Review this pathway.

 

Pontine damage causes pontine ipsiversive gaze palsy by damage of the ipsilateral PPRF.

Left MLF damage causes left INO. Limitation of adduction of the left eye. Slow adducting saccades in the right eye. Spared convergence. Impaired vertical VOR. The cardinal diagnostic feature is a slow adducting saccade. The other features are not specific.

 

One and a half syndrome

-         PPRF or abducens nucleus damage

-         MLF damage

-         only the opposite eye can abduct (pontine exotropia)

-         spared convergence

 

Wernicke’s encephalopathy

-         confusion, ophthalmoplegia, ataxia

-         vertical or horizontal gaze palsy, or INO +/- nystagmus

-         Rx with thiamine

 

 

Cerebral paresis of horizontal gaze

-         acute massive frontal, parietal, or deep hemispheric lesion causes contraversive saccadic palsy.

-         Two saccadic commands

o       Trigger to turn off pause cells

o       Retinal error or desired eye position signals

-         Two classes of saccades

o       Reflexive

o       Volitional

-         Parallel redundant pathways of the frontal and parietal eye fields, going through the superior colliculus to the PPRF.

-         To permanently abolish saccades, you need to damage the frontal eye field and the superior colliculus, but the superior colliculus is rarely damaged.

 

Horizontal gaze deviation in coma

-         Cerebral hemispheric - ipsilateral

-         thalamic - contralateral

-         pontine - contralateral

-         cerebellar – contralateral

 

COWS – cold opposite, warm same (nystagmus)

CUWD – warm up, cold down

Works only in conscious patients. In coma, no nystagmus so eye movement is reversed.

 

Pretectal syndrome

-         paralysis of upwards saccades

-         paralysis of upward saccadic and pursuit

-         paralysis of upward gaze and VOR

-         retraction and convergent oscillations

-         eyelid retraction

-         light-near dissociated enlarged pupils

 

Tonic vertical eye deviation in coma

-         upward deviation

o       anoxic coma

o       cerebellar hemorrhage

-         downward deviation

 

Saccade paresis

-         PPRF burst or pause neuron lesion

o       infart

o       Demylienation

o       Neoplasm

-         Degeneration

o       SCA1 and 2

o       PSP

o       Huntington’s

-         Lipitoses

o       Tay-Sach

o       Gaucher

o       Niemann Pick C – vertical

-         Peripheral neuromuscular disease

o       – CPEO

o       Thyroid myopathy

o       Myasthenia – only with repeated movements

o       Nerve palsy