16537018
Description
Flashcards by Caitlin Murphy, updated more than 1 year ago
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Created by Caitlin Murphy
almost 6 years ago
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| Question | Answer |
| Accommodation | enables us to look at and focus upon objects close to the eye |
| Cillary body contraction ... | relaxes suspensory ligaments enabling the lens to recoil (makes it fatter) |
| Process of accommodation | |
| Argyll-Robertson (Prostitute's) pupil | No pupillary reflex but accommodation reflex is ok seen in: tertiary neuro syphilis & diabetic neuropathy |
| Edinger-Westphal nuclear damage | No direct or consensual reflex on damaged side Pupil dilated & unreactive Cause: vascular/tumour/brainstem |
| CN III compression | No direct or consensual reflex on damaged side Pupil dilated and unreactive CNIII Compression = loss of all CNIII functions |
| CNIII Vascular lesion | = sparing of pupillary functions |
| Superior tarsal muscle | Smooth muscle, innervated by sympathetic NS – open eyes more during fight or flight or by pharmacological reasons. Not able to open eye by itself. Loss will show partial ptosis in the eye |
| All extraocular muscles are innervated by... | CN III except: Superior oblique (the muscle with a trochlea) = trochlea nerve (CN IV) Lateral rectus (the abductor muscle) = abducens nerve (CNVI) |
| SR – Superior rectus IR – Inferior rectus MR – Medial rectus LR – Lateral rectus SO – Superior oblique IO – Inferior oblique | |
| Origin of rectus muscles | a common tendinous ring at posterior of point |
| Nerves that come through superior orbital fissure | CN III CN IV CN Va CN VI |
| tumour of meningies effect of eyes | loss of eye movements headache (CNVa) |
| Origin or inferior oblique | antero-medial floor of the orbit (is like a hammock sitting under the eye) |
| The 3 perpendicular axis eye can move | Black axis: Transverse = Look left or right Red axis: Sagittal = Look up or down Blue axis: Coronal = Torsion (twisting in and out) Some muscles bring about combined eye movements |
| Eye testing pattern and what they test | |
| Contraction of Lateral rectus | abducts eye |
| contraction of medial rectus | adducts eye |
| Contraction of the superior rectus | elevates the eye look up |
| Contraction of the inferior rectus | depresses the eye look down |
| Contraction of superior oblique | tilts eye downwards |
| contraction of inferior oblique | tilts eye upwards |
| Hering's law | extraocular muscles normally have equal and simultaneous innervation |
| If a given CN VI or its nucleus is damaged | No lateral movement of the affected eye. Ipsilateral eye rests in adducted position = convergent squint. Horizontal diplopia. Diplopia worse when looking toward the affected side. |
| CN III is the motor supply for... | the x4 muscles that move the eye, x1 that opens the eyelid, the sphincter pupillae, the ciliary body |
| CN III lesion can produce | Complete ptosis on affected side. Down and out position of affected eye. Divergent squint. Horizontal and vertical diplopia. Dilated pupil on affected side that’s unreactive to direct or consensual light. Consensual pupil reflex intact in contralateral (unaffected) eye. |
| Patient can complain of sore neck | loss of muscles (due to CN IV lesion) that mean eye can't rotate properly so at rest eye is not pointing straight ahead. Patient bends neck to correct this - hence pain |
| Motor supply to superior oblique | CN IV |
| CN IV lesion can produce: | Upward deviation and extorsion (outward rotation) of the affected eye. Vertical diplopia: worse when descending stairs / reading paper. Torsional diplopia: double vision where the images twisted apart from each other. Patient tilts head away from lesion to help prevent diplopia (counteracts extorsion produced by inferior oblique). |
| Track target definition | smooth pursuit when target is moving |
| stabilise target definition | you are moving target is not |
| scan target to target | saccade (fast movement) |
| centre that control eye movement | Vestibular nuclei & parapontine reticular formation Frontal eye field (frontal cortex) Saccade centres (several locations) Visual association areas |
| what is the medial longitudinal fasciculus? | is a neuronal tract that enables conjugate gaze & tracking neck movement connects CNIII, IV and VI with vestibular nuclei, cerebellum & neck muscle lower motor neurons (makes you look left or right) |
| Pathway of the medial longitudinal fasciculus | Action potential travels from CNVI to CNIII Involved in lateral gaze (& other things too) Under automatic & voluntary control |
| Lesions of the medial longitudinal fasciculus results in | Internuclear opthalmoplegia Lesion cuts interneuron connections between CN VI & CN IIII means you can't move your eyes properly Can be bilateral or unilateral Can still accommodate |
| vestibulo-occular reflex | A rotation of the head is detected, which triggers an inhibitory signal to the extraocular muscles on one side and an excitatory signal to the muscles on the other side (semicircular canal is activated). The result is a compensatory movement of the eyes. |
| Testing of vestibulo-ocular reflex: | in comatose patients to determine brain stem function - Doll's eye sign positive is good |
| Signalling to a given lateral semicircular canal increases if... | ...head is rotated to toward & decreases if head is rotated away from it |
| Effect of brainstem stroke on vestibular system | on affected side the lateral semicircular canal is not activated and the patient's eyes drift off to opposite side and snap back (nystagmous) |
| Which direction will a right lateral semicircular canal or vestibular nucleus make the eyes look? | to the left |
| Right (VN, LSCC OR FEF) makes you look... | Left damage causes the eyes to drift/look right |
| Jerk nystagmous definition | Repetitive eye movement with a fast and slow phase is described according to the fast phase EXAMPLE: Slow Phase: Eyes slowly drift left....they look towards the damaged left side Fast Phase: Eyes move quickly rightwards back to the midline via action of saccade centres in brainstem & cortex |
| Result of putting cool/cold water into an external auditory meatus | it mimics a vestibular system/nucleus lesion on that side |
| Result of cold caloric test | can be used to induce nystagmous & test brainstem function |
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