Visual Pathway Flashcards
Define visual field
everything you see with one eye
What is two visual field tests
Confrontation test - move hands till appears in patients visual field
Automated perimetry - Patients focus on central light on the machine and press joystick when see additional light appear in their periphery
What is the purpose of the confrontation and automated perimetry tests
Map out visual field
does Visual acuity test your visual field
No, Measures the distance you can read from
What is the 4 basic steps in the visual pathway
Optic nerve
Optic chiasma
Optic tract
Optic radiation
Where does the optic nerve leave the orbit through
The optic foramen into medial cranial fossa
What is the point in the visual pathway were nerves merge together
Optic chiasma
What occurs at the point of the optic chiasma
Nasal fibres cross to the opposite sides
Where does the optic tract synapse
At the lateral geniculate body in the thalamus
What fibres does the optic tract contain
Optic tract contain fibres from the (lateral) temporal half of the ipsilateral eye and the crossed over over nasal fibres from the contralateral eye
Where does the optic tract axons synapse
At the lateral geniculate body in the thalamus
How does the optic nerves travel through the cerebral hemisphere
As optic radiation
Where does the optic radiation travel to
The optic radiation passes behind the internal capsule (retro-lentiform fibres) to reach the primary visual cortex in the occipital lobe
What does the primary visual cortex receive from optic radiation
an action potential
Why does the right visual cortex see he left half of the visual field
When the nasal fibres cross over at the chiasma
(nasal go to the opposite optic tract and temporal remain in thee same optic tract)
Therefore the left visual field fibres are all traveling in the right optic tract which then sends action potential to the right occipital lobes visual cortex
What occurs when the right optic nerve is damaged
Right eye blindness
What occurs when the optic chasm is disputed in the middle
Nasal fibres are damaged meaning the temporal field of vision is affected but the nasal field of vision is fine
= Bitemporal hemianopia
What is a common cause of bitemporal hemianopia
Pituitary gland enlargement as sits below point of optic chiasma
What occurs when the right optic tract is damaged
The left visual field of both sides is lost
Causing contralateral homonymous hemianopia
When right optic tracts temporal fibres are damaged what visual field does this affect
Damaged temporal fibres from the right optic tract means nasal field vision from right eye is lost
When right optic tracts nasal fibres are damaged what visual field does this affect
Damaged nasal fibres from the right optic tract means temporal visual field from the left eye is lost
Why is it “contralateral” homonymous hemianopia
As the damages occurs in one of the optic tact but affects both eyes
When visual lesions are symmetrical what does this usually indicate
lesion is occurring in optic tract
When either left/right visual field is lost n both eyes, where is the lesion
In the opposite optic tract
What occurs when there is optic radiation damage
Contralateral homonymous hemianopia
Define hemianopia
The loose of half your field of vision
