NS 20 vision Flashcards
what is the basic structure of the eye?
3 layes
- sclera +cornea
- choroid/ ciliary body/ iris
- retina
describe the features of sclera/ cornea
- tough connective tissue
- sclera white
- cornea transplant
describe the features of the choroid/ ciliary body/ iris
- highly vascular
- choroid ; absorbs aquous humour
- iris - regulates light entering eye
what does the retina contain?
contains photoreceptors such as rods and cones
what are the 2 fluid filled cavities called?
aqueous humor
vitreous humor
how does glaucoma arise?
flow of aqueous humor from posterior to anterior chamber- disruption of balance of flow
what do the ganglion cells respond to?
contrast movement, colour and detail
what is the fovea?
the central portion of the eye that only contains cones
sharpest vision and greatest colour discrimination
what does the optic disk not contain?
no receptors
what are the reasons for the fovea’s high visual acuity?
- thinning if retinal layers
- lack of rods, high concentration of cones
- low convergence
what produces a blind spot?
lack of rods and cones at blind spot
what are the elements of the pathway?
optic nerve optic chiasma optic tract lateral geniculate body of thalamus optic radiations striate cortex (primary visual cortex)
trace the pathway from the right visual feild
- right visual field
- imaged on left retina
- temporal fibres dont cross
- nasal fibres cross at optic chiasma
- right field represented in left - optic tract
- relay/processing in LGN
- projects to left primary visual cortex
where is the left half field represented?
in right optic tract
projection from upper retinal quadrant arise from where?
lower visual field
which sulcus have the projections from upper righ retinal field on top of it and the lower projections below it?
calcarine sulcus
what is the blood supply to the primary visual cortex?
largely posterior cerebral
list the 4 types of blindness occuring due to lesions in the pathway (look at diagram )
- monocular blindness
- bitemporal hemianopia
- homonymous hemianopia
- upper quandrantanopia
what is the pupillary light reflex?
adjust the site of pupil in response to light
decribe the route of the afferents
retinal ganglion cell
pretectal region
oculomotor nuclei
ciliary ganglion
which muscle constricts the pupil?
cell bodies in the ciliary ganglion project to muscles which constrict to the sphincter pupil
do the afferents in a light reflex pass directly to pretectal regions?
yes
what is the accommodation reflex?
an automatic response from when you switch focus from an object thats far away to one that is closer
this response enables you to switch between objects and maintain focus
when looking far away are muscles relaxed or constricted?
relaxed
define normal vision
able to focus both distant and near objects
define myopia and give treatment
- short sighted
- able to focus on near objects
- unable to focus on distant
- eye ball relatively too long
- treatment concave lens to diverge light
define hyperopia
- long sighted
- unable to focus on near objects
- eye ball relatively too short
- treatment convex lens to converge light
define presbyopia
- normal age change
- gradual loss of accommodation
- lens are less elastic
- ciliary muscles are weaker
- near point; 100mm in young adults
- 800 mm in old age
treatment convex lens to converge light
define saccade gaze shifts
rapid gaze shift to fix peripheral object on fovea
what does saccade involve?
OPPOSITE frontal eye field (forntal lobe)
define pursuit movements in gaze shift
smooth movements to keep objects fixed on fovea
where is it intitated? (pursuit)
in visual cortex of SAME SIDE
what are the effects of acommodation reflex?
- lens thickening
- pupillary constriction
- convergence of the eye
