The eye and vision; visual pathways Flashcards
What are the three parts of the visual system?
- Eyeball - optical front end and retina/optic disk at the back
- Connections - optic nerve, optic chiasm, optic tract, LGM, optic radiations
- Brain - occipital, temporal, frontal and parietal lobes
What is the most common refractive error?
Presbyopia
Define presbyopia
gradual loss of your eyes ability to focus on near by objects
Define myopia
can see objects near to your clearly, but objects further away are blurry
What is the lens correction for myopia?
CONCAVE (minus) lenses
Define hypermetropia
nearby ojects are blurred, but vision is clearer when looking at objects further away
What is the lens correction for hypermteropia?
convex lens
What is the retina?
layer at the back of the eye that contains cells sensitive to light
What are the two types of cells in the retina?
rods and cones
What are the main features of rod cells
- 120 million onretina
- high convergence to ganglion cells
- greyscale vision
- very light sensitive
- widespread distribution
- broad spectral senstivity
What are the main features of cone cells?
- 6 trillion in retina
- lower convergence to ganglion cells
- colour vision (red, green, blue)
- 1/30th of sensitivity of rods
- concentrated in the macula
- narrow spectral sensitivity
What is the consequence to vision if the right optic nerve was severed?
Loss of sight in the right eye only
What is the consequence to vision if there is damage at the optic chiasm
bitemporal hemiaponia
What is the consequence to vision if there is temporal lobe damage
superior quadrantanopia
What is the consequence to vision if there is damage to the parietal lobe?
Inferior quadrantanopia
What is the consequence to vision if there is damage to the right occiptal lobe
left hemianopia
Describe the WHAT (ventral) stream
running through the temporal lobes; tells you what the thing is
Where is the visual library of the brain?
temporal lobes
Describe the where stream of the brain
going through the parietal lobes. Appraises the overall visual scene and allows the brain to see one thing amongst many
Where is the attention centre of the brain
parietal lobes
Where is the action based vision centre of the brain
frontal lobe
excecutes a plan based on what it has seen
What is simultanagnosia and what causes it?
diffuclty finding one thing amongst many
bilateral parietal brain damage
What is achromatopsia? And what causes it?
unable to see in colour
bilateral anterior occipital brain damage
Define visual acuity
the ability of the vision system to resolve (‘see’) a gap between two points. This is known as spatial resolution
What are the two main types of sight impairment?
- Sight impairment (SI)
- Severe signt impairment (SSI)
RAPD –>
Relative Afferent Pupillary Defect
A condition in which the pupils respond differently to light stimuli shone in one eye at a time due to unilateral or asymmetrical disease of the retina or optic nerve
What are the causes of RAPD?
- Optic neuritis
- Anterior ischaemic optic neuropathy (AION)
- Tumour pressing on the optic nerve
- Glaucoma
What is opacity in the eyes?
stops light passing through the cornea to the retina and may cause the cornea to appear white/clouded over
What is the retinal reflection test?
“RED REFLEX”
When light passes through the pupil and is reflected back of the retina to a viewing aperture, creating a red glow
*blue in black people*
What can the retinal reflection test identify?
- corneal scar
- cataract
- retinoblastoma
Leukocoria =
“white pupil”
when the pupil is white rather than black
What are the key elements to obserbe when examining the optic nerve?
Margin, colour and cup
What are the causes of a swollen optic disc?
- Pseudo swelling
- Small discs
- Calcium deposits ‘drusen’
- Genuine swelling
- Optic Neuritis (VA reduced)
- Raised ICP (VA normal)
- SOL
- IIH
- Hydrocephalus
What extra-ocular eye muscle(s) are supplied by:
CN IV
Superior oblique
What extra-ocular eye muscle(s) are supplied by:
CN III
- inferior rectus
- inferior oblique
- superior rectus
- medial rectus
What extra-ocular eye muscle(s) are supplied by:
CN VI
Lateral rectus
Features of 3rd CNP
- Vertical diplopia
- Eye is “down and out”
- Diplopia every where
- Pupil dilated and ptosis
- Can be associated with aneurysm – needs urgent brain imaging and angiogram
Features of 4th CNP
- Oblique diplopia
- Head tilt away from side of the lesion
- Diplopia worse away from the side of the palsy if unilateral (adduction)
- Common after head injury
- Bilateral – might be congenital
Features of 6th CNP
- Horizontal diplopia
- Worse in far distance
- Worse towards the side of the palsy if unilateral
- Bilateral – concerned that raised intracranial pressure is present
What are the main worldwide causes of blindness?
- cataract
- age related macular degeernation
- glaucoma
- tachoma
- diabetic retinopathy
- refractive error
Action of superior rectus
Main movement is elevation. Also contributes to adduction and medial rotation of the eyeball.
Action of inferior rectus
Main movement is depression. Also contributes to adduction and lateral rotation of the eyeball.
Action of medial rectus
Adducts the eyeball.
Action of lateral rectus
Abducts the eyeball.
Action of superior oblique
Depresses, abducts and medially rotates the eyeball.
Action of inferior oblique
Elevates, abducts and laterally rotates the eyeball.
