Lecture 19 - Eye movements: Disorders (LA) Flashcards
Diplopia
Double vision
a) Ocular myasthenia?
b) What happens when it is systemic?
c) What is it treated by?
d) How is the post-synaptic membrane affected?
a) Autoimmune disorder where AchR on the extraocular muscles are attacked by the immune system, leading to fatigue (hence droppy eye and no eye muscle movement)(most common area being the EOM/levator)
b) When systemic (myasthenia gravis) - if muscles of swallowing or breathing are affected (aka myasthenic crisis) hence why dsyphagia (difficulty swallowing) can be a sign of myasthenia gravis
c) Treated with tensilon (edrophonium), a short acting anticholinesterase where administration fixed droppy eye and eye movement
d) Folds (usually deep and full of ACh-esterase which breaks down ACh) are shallower and Ach-esterase is closer to Ach receptors (inactivating Ach as soon as it is released)
T/F - In ocular myasthenia, saccades may appear to be overly fast or slow
T
Internuclear opthalmoplegia (INO)
Damage to the medial longitudinal fasciculus If it is interrupted then the left eye can still abduct (look to the left) but the right eye cannot adduct (cannot look to the left).
Medial longitudinal fasciculus location and what is it vulnerable to?
Runs from interneurones in the abducens (6th nerve) nucleus in the pons up to the oculomotor (3rd nerve) nucleus in the midbrain, crossing the midline as it goes to the other eye. It is vulnerable to disease (MS in particular)
Yoke?
To put to work
Nystagmus (invol. eye movement) in abducting eye - general idea is that one eye is not adducting causes the other abducting eye to overshoot (this leads to double vision) but they eventually get on target
Nystagmus (invol. eye movement) in abducting eye - general idea is that one eye is not adducting causes the other abducting eye to overshoot (this leads to double vision) but they eventually get on target
Commonest causes of INO? How about in older patients? What happens if lesions are large enough?
MS - MLF is a site for a demyelinating plaque Stroke or tumour in older patients Vergence can also be affected as well as adduction
T/F - In INO, Vergence can also be affected as well as adduction
T
T/F - In INO you may still converge (move eyes towards the middle)
T
Misdirection syndromes
Sometimes nerves get crossed, either at birth or later, as a result of trauma
Duane’s congenital retraction syndrome - what is it? How does one get it?
Benign condition where the hallmark is a unilateral or bilateral abducens palsy (limited abduction)- often, attempted adduction leads to a retraction of the affected eye into the orbit Loss of 6th nerve - The 3rd nerve knows the lateral rectus is not innervated (when 6th nerve is absent) - 3rd nerve also innervates it, hence retracting eye back into the orbit
When a nerve is damaged by trauma - the nerve tries to repair things by sprouting new fibres BUT it may not connect where it should e.g. Aberrant regeneration of the 3rd nerve which leads to?
The eye doing the opposite or irrelevant action e.g. 3rd and 6th nerve get mixed so while looking at right, left eye responds with abduction
Nystagmus - what is it and how is it treated?
Ocular oscillation initiated by a slow movement of the eyes off-target - most often followed by a fast eye movement bringing them back towards the desired point of fixation Either treated by surgery or using prisms in glasses
Oscillopsia
Objects in the visual field appear to oscillate. The severity of the effect may range from a mild blurring to rapid and periodic jumping
