Visual fields and loss Flashcards
What can cause visual field loss?
Damage to: Retina Optic nerve Chiasm Optic tract Optic radiation Cortex
What kind of visual loss does damage to the retina cause?
Horizontal (lose top or bottom)
Where does vertical visual loss result from?
Optic nerve or posterior
What kind of visual loss does an optic nerve lesion lead to?
Monocular blindness- all from 1 eye gone
What kind of visual loss does an optic chiasm lesion lead to?
Bitemporal hemianopsia- lose peripheral fields
What kind of visual loss does an optic tract lesion lead to?
Contralateral hemianopia/Homonymous hemianopsia- lose same side
What kind of visual loss does an optic radiation lesion lead to?
Quadrant Hemianopsia- just lose quarter on same side
What kind of visual loss does a cortex lesion lead to?
Bitemporal Hemianopia with foveal sparing
Why do you get foveal sparing with a cortex lesion?
Due to number of fibres going from fovea to cortex meaning affecting all is hard
What can lead to damage of the optic nerve, chiams, tract, radiations or cortex?
Vascular disease Space occupying lesion Demyelination Trauma Neuritis
How does neuritis progress?
Progressive unilateral visual loss
Colour desaturation (colours appear washed out)
Gradual recovery
Describe the visual pathway
Light strikes retina
Retina becomes optic nerve
Nasal portion of optic nerves cross at chiasm
Optic nerves become optic tract at chiasm
Optic tract becomes optic radiations at Lateral Geniculate Nucleus
Optic tracts go north and south to visual cortex
What is the term for a normal eye?
Emmetropic
Describe the focus of the lens
Light diverges from point
Further away point light diverges more therefore requires thinner lens with greater angle to focus on retina
Closer light diverges less therefore requires thicker lens with less angle to focus on retina
What does a convex lens do?
Focus light down
What does a concave lense do?
Spread light out
What is a myopic eye?
Nearsighted- eyeball is too big to focus distant light on retina
Why can’t a myopic eye focus distant light?
Lens is too thick therefore light exits with a smaller angle and focuses in posterior chamber
What is a hyperopic eye?
Longsited- eyeball too small to focus near light on retina
Why can’t a hyperopic eye focus near light?
Lens is too thin therefore light exits with a larger angle and focuses behind eye
What kind of lens can help in myopia?
Concave back
Why can a concave lens help in myopia?
Diverges light more therefore enters and exits lens with greater angle
What kind of lens can help in hyperopia?
Convex front
Why can a convex lens help in hyperopia?
Focuses light down so enters and exits with less angle
How big is a normal eyeball?
~22mm
How big is a myopic eyeball?
~33mm
How big is a hyperopic eyeball?
~18mm
A lesion to which lobe of the brain will give a top field loss?
Temporal
A lesion to which lobe of the brain will give a bottom field loss?
Parietal
