OPTH Lec06 Flashcards
What is diplopia?
Seeing two of the same object
What is the key thing to distinguish with a diplopic patient?
Whether the diplopia is monocular or binocular
When would a patient who have diplopia have monocular diplopia?
When you cover an eye and the double vision remains
Is monocular or binocular diplopia a neurologic problem?
Binocular
What causes monocular diplopia?
Refractive problem in the front part of the eye (not in the retina or further back in the neuron pathway)
What is the most common cause of monocular diplopia?
Astigmatism - abnormal curvature of the corneal surface (can be caused by corneal deformation or tight corneal stitches after surgery)
What are other causes of monocular diplopia?
cataract irregularities, lens displacement, primary problems with corneal curvature such as keratoconus
Why does binocular diplopia occur?
Because the eyes don’t move in sync with each other (CN lesion of CNIII, CNIV, CNVI), extraocular muscle abnormalities(muscle fibrosis that occurs with Grave’s disease) derangements at the neuromuscular junction (myasthenia gravis)
What can cause an individual nerve palsy?
Microvascular disease, stroke, tumor, aneurysm
What happens when you knock out CNIII?
Most eye muscles are innv by CNII so the eye will deviate DOWN AND OUT (because the abducens and superior oblique will pull on it). PTOSIS (due to levator palpaebrae) and BLOWN PUPIL (parasymp from Edinger Westphal)
Paralysis of what muscle causes ptosis?
levator palpebrae (innv by CNIII)
What causes most CNIII palsies?
Ischemia secondary to DIABETES or HTN
Where will aneurysms causing CNIII palsies occur?
Junction of the posterior communicating artery and the internal carotid artery
Compressive lesions of CNIII will affect which component of the nerve?
The parasympathetic and cause a blown pupil = EMERGENCY
What do you do when you have pupillary involvement?
MRI and ANGIO
What are the common sites of Cerebral Aneurysms?
Anterior communicating artery, anterior cerebral, internal carotid, posterior cerebellar, superior cerebellar, basilar, vertebral, posterior communicating, middle cerebral
Why do oculomotor palsies involve the pupil?
Because the parasym never innervating the iris travel with the third nerve
What does pupillary involvement suggest?
compressive lesion (vascular lesion will spare the pupil); parasymp nerves course the surface of CNIII; damaged by compression from outside (aneurysm from PCA, boney structure, uncal portion of the temporal lobe)
What can cause an ischemic lesion?
HTN
Which part of CNIII will an ischemic lesion affect?
Inside; affect the motor component, spare the parasymp
If your patient is presenting with CNIII loss and pupillary involvement, what do you do?
order MRI and angiogram
If there is a CNIII palsy and there isn’t pupillary involvement; what would you suspect?
Vaso-occlusive problems; check glucose and bp
What does the abducens nerve control?
The lateral rectus muscle
What would a CNVI lesion look like?
eye will not be able to abduct; patients will be cross-eyed; will turn their head to avoid double vision
What is the pathway of the abducens?
Starts in the pons; exits the brainstem at the Ponto-medullary junction; runs up the floor of the skull through cavernous sinus into the orbit.
Where is CNVI most susceptible to high intracranial pressure?
When it enters the cavernous sinus; makes a 90 degree bend; patients with high ICP from a tumor have a CNVI knocked out
Why do you cry when you see food?
Because if you have an aberrant regeneration of CNVII, the nerves that would normally control salivation will go to the lacrimal gland
What would happen if you had aberrant regeneration after CNIII palsy?
Nerve regeneration can get mixed up, looking medial may cause eyelid to shoot up (inappropriate contraction of levator palpebrae)
In what situations do you get aberrant regeneration?
trauma or mass lesions - not with microvascular events
What does the trochlear nerve (CNVI) innervate?
Superior oblique muscle
How will a patient with a CNIV lesion present?
upward deviation of the affected eye and twisting of their eye which will make them TILT THEIR HEAD AWAY FROM THE LESION
What can cause a CNIV lesion?
trauma, ischemic event, congenital
Why is CNIV more susceptible to injury than the other one?
Be it is the skinniest and RUNS THE LONGEST DISTANCE inside the cranial vault and EXITS FROM THE BACK of the brainstem so can be pulled from the root.
What are caused of a CNIV palsy?
Trauma, tumor, congenital, ischemia
How do you determine whether a CNIV is congenital?
Ask for history and look at old photos for head tilt; neck pain
What does the trochlear muscle do?
From the back of the orbit forward through the trochlear pulley; inserts AT THE BACK OF THE EYE.