Vision 2 Flashcards
What is your visual field?
Everything you see with one eye including the periphery
How is visual field assessed?
By confrontation test or automated perimetry
At the optic chiasma, which type of fibres cross to the opposite side?
Nasal fibres
What kind of fibres does the optic tract contain?
Contains fibres from the (lateral) temporal half of the ipsilateral eye and the crossed-over nasal fibres from the contralateral eye.
In terms of visual field, the optic tract contains all the fibres from the opposite half of the visual field
Where do the fibres from the optic tract synapse?
At the LGB of the thalamus
(Lateral geniculate body)
Where do the fibres travel after reaching the LGB?
Optic radiation travels to reach the primary vidual cortex in the occipital lobe
Thus the Right visual cortex sees the left half of the visual field and vice versa.
What damage do you expect when the right optic nerve is damaged?
Blindness in one eye
What damage do you expect when the optic chiasma is damaged in the middle?
Bilateral hemianopia
What damage would you expect with a right optic tract/right optic radiation that is damaged?
Contralateral homonymous hemianopia
What sits below the optic chiasm?
Pituitary gland
Look
What are intrinsic muscles responsible for?
Control pupil diameter & helps alter lens curvature to enable us to see near objects
What are extrinsic muscles responsible for?
They move the eye
What is the origin and insertion of the eye muscles?
What supplies the superior oblique muscle?
The trochlear nerve (CN 4)
What supplies the lateral rectus?
The abducens nerve (CN6)
Apart from the superior rectus and the lateral rectus, what are the other extrinsic muscles supplied by?
Occulomotor nerve (CN3)
What are the following terms for binocular eye movement?
Dextroelevation, elevation, levoelevation
dextroversion, …………..levoversion
Dextrodepression, depression , levodepression
When the lateral rectus is abducting the eye, what is the action of the superior rectus and the inferior rectus?
SR - Causes elevation
IR - causes depression
When the medial rectus has the eye adducted what is the action of the superior rectus and the inferior rectus?
SR causes intorsion
IR causes extorsion
What is the action of the superior oblique and the inferior oblique when the eyeball is abducted?
Superior oblique - intorsion
Inferior oblique - extorsion
What are the actions of the msucles of the eye?
MR
LR
SR
IR
SO
IO
Define strabisumus
Squint
What are the names given to the two types of squint?
Esotropia - manifest convergent squint
Exotropia - divergeant squint
What is amblyopia?
Lazy eye
What is the cause of amblyopia?
Brain supresses the image of one eye leading to poor vision in that eye without any pathology (correctable in early years using eye patches to stimulate the “lazy” eye to work)
What is diplopia?
Double vision
What is often the cause of diplopia?
Usually occurs in squints as a result of nerve palsies
What is the sympathetic and parasympathetic response to an increase / decrease illumination?
Incerase illumination - parasympathetic resoponse - both pupils contract
Decrease illumination - sympathetic - pupils dilate
Where do fibres destined to activate the pupillary refles travel after the optic tract?
They don’t travel to the LGB, instead they travel to the midbrain where the third cranial nerve nucleus is situated
What is the blue part of the diagram? What is its significance
It is the part of the nucleus of the third cranial nerve called the Edinger Westphal nucleus - It is for the parasympathetic fibres. The pupillary reflex goes down the the EWN on both sides
What is the travel of the efferent impulses from the EWN?
Preganglionic fibres pass through the third cranial nerve into the orbit, they go to and synapse in the ciliary ganglion, postganglionic fibres go through short ciliary nerves to the constrictor papillae
What is the name given to pupils being different sizes?
Aniscoria - happens in horner’s syndrome
What is another pupil defect besides aniscoria?
Abnormal light reflex - pupils react abnormally to light
What are some of the common causes of absent / abnormal pupillary reflex?
Any abnormality of the afferent limb centre / efferent limb centre of the reflex
Diseases of the retina - detatchment, degenerations of dystrophies
Diseases of the optic nerve - such as optic neuritis seen in MS
Diseases of the 3rd cranial nerve (efferent limb)
If a patient with diabetes has 3rd cranial nerve palsy, and also has an absent pupillary reflex, what is a possilbe diagnosis?
Cerebral artery eneurysm - emergency
Why does horners syndrome result in aniscoria?
Due to damage to the sympathetic inenrvation to the pupil
What are other signs of horners syndrome besides the abnormal pupillary reflex?
Includes ptosis and anhidrosis
Where do postaganglionic sympathetic fibres travel alongside?
Travel along with blood vessels in the head and neck
Horner’s syndrome can occur due to disruption at any point. An example would be Pancoast’s tumour of the lungs!
