Eye muscles - Intrinsic Flashcards
What is the overall function of the intrinsic muscles
Control the pupil diameter and helps alter the lens curvature to enable us to see near objects
What is the three intrinsic muscles in the eye
Ciliaris muscle
Constrictor pupillae
Dilator pupillae
Where is the cillaris muscle found
In the ciliary body
What is the constrictor pupillae found
In the iris at the pupillary boarder
Where is orientation of the dilator pupillae and where is it found
Radially running muscle in the iris
What innervates the ciliaris muscle
Parasymapthetic component of the Oculomotor CNIII
What innervates the constrictor pupillae
Parasymapthetic component of the Oculomotor CNIII
What innervates the dilator pupillae
Sympathetic from the plexus around the blood vessels
What is the pupillary reaction to increased illumination
Parasympathetic innervates the constrictor pupillae muscle and both pupils constrict
What is the pupillary reaction to decreased illumination
Sympathetic innervates dilator pupillae muscle and both pupils dilate
What is the steps in examining pupillary reflex
Start in dimly lit room - with pupils dilated
Pen torch in front of one eye check for both pupils constricting (Direct and consensual reflex)
Swing light to other side should remain both pupils constricted
What is the pathway if the pupillary reflex differ to the light pathways
Light falls on retina and follow normal path to optic tract, fibres then destined to active pupillary reflex leave optic tract and travel to the midbrain to the Oculomotor nucleus
What part of the occulomotor nucleus (IIIn) does the parasympathetic fibres travel
Edinger- Westphal nucleus
What side of the EWN does pupillary reflex fibres go
Both sides
Where does the preganglionic parasympathetic fibres from the EWN travel and synapse in the efferent pathway of the pupillary reflex
Pass into the orbit and synapse in the ciliary ganglion
Where do postganglionic fibres travel and what do the stimulate in the pupillary reflex
Travel through short ciliary nerves to constrictor pupillae and cause pupil constriction of both sides
What is is called when pupils size may be different
Anisocoria
What occurs in an abnormal light reflect
Pupils may look normal but react abnormally to light
What are common causes of abnormal/absent pupillary reflex
Any abnormality of the afferent limb/ centre / efferent limb of the reflex
Diseases of the retina – detachment/ degenerations or dystrophies
Diseases of the optic nerve – such as in optic neuritis (frequently seen in MS)
Diseases of the III cranial nerve (efferent limb)
Why is it important to check pupillary reflex if you see a patient with CNIII
As in conditions of diabetes CNIII palsy, there is usually no damaged to parasympathetic fibres
What is suspected in a diabetic patient if they have CNIII palsy and pupillary reflex is absent
Suspected cerebral artery aneurysm
How does anisocoria occur in Horners syndrome
Anisocoria due to damage to the sympathetic innervation to the pupil affecting the dilation of the pupils
What are additional signs of Horners syndrome
You might also see ptosis
(drooping of the eyelid) on the affected side
anhidrosis (loss of sweating on the affected side)
What is the paths of sympathetic innervation to the eye
Thoracolumbar outflow of the sympathetic goes down the sympathetic chain and cervical ganglia and the postganglionic sympathetic fibres travel along the blood vessel
Where can horners syndrome occurs
occur any point of sympathetic pathway
