Vision Flashcards
How much light does the cornea bend?
2/3
How much light does the lens bend?
1/3
Hypermetropia?
Long sightedness _ eyeball too short or lens too weak
Myopia?
Short sightedness - eyeball too long or lens too strong
Refractive power is measured in?
Diopters {D}
Refractive power and focal length?
2d has focal length of 0.5m
It is reciprocal
What kind of corrective lens is needed?
Hyperopic-converging myopic- diverging
How many receptors?
120 million rods (dim)
5 million cones (bright)
Processing layers of retina?
3 direct-receptors, bipolar cells, ganglion cells
2 transverse layers- amacrine and horizontal cells.
How does rhodopsin work?
Photosensitive pigment in rods
When photon hits the retinal. It causes 11 cis to all trans flip causing closure of cGMP gated cation channels which are open in the dark leading to hyperpolarisation of the photoreceptors and a reduction in the release of glutamate
Ganglion cell response?
Local contrast on and off lateral inhibition.
What kind of potential in retinal cells?
Ganglion - action potential receptors and bipolar - graded potential
Colour wavelength?
Red: 560
Green: 530
Blue: 420
Rods: 500
Genes for green and red are where?
X chromosome
So males colour blindness is 7%
And 0.5% in females
Where is blue colour gene?
Chromosome 7
Central achromatopsia?
Damage to cortical colour processing area V4
What is simple cell response in V1?
From rows of ganglion cells or LGN, on and off centre fields
Brodmann 17 area is divided into?
Ocular dominance columns, orientational columns and colour blobs.
Hypercolumn contains all 3
Homonymous hemianopia?
After optic chiasam lesion so you lose same side of both eye, both lefts
Bitemporal hemianopia?
Can’t see lateral sides of eyes, this is due to compression or damage to optic chiasm
Scotoma?
Could be defect in area of visual field, retinal damage pressure of tumours restricting th optic never, chiasm, optic tract or optic radiation
Ventral stream is responsible for?
To temporal cortex, object identity and conscious perception
Dorsal stream is responsible for?
To parietal cortex,location, motion and action.
Visual agnosia?
Inability to recognise visually presented objects.
Cannot identify orientation of card in slot?
Optic ataxia?
Can describe but not act. So knows orientation but cannot place card in slot
Prosopagnosia?
Inability to recognise faces, in fusiform gyrus in temporal lobe.
Blindsight?
Destruction in v1, leading to blindness in that area, individuals can still perform discrimination tasks.. happens because projections from LGN and superior colliculus reach cortical, areas bypassing V1
What does vestibulo ocular reflex do?
Stabilises gaze by countering movement of head
Optokinetic reflex?
Stabilises image of moving object on retina
What happens in pupillary reflex?
Illumination Will cause contraction of both eye due to pretectal nuclei and edinger- westphal nuclei.
How many retinal ganglion cells per eye?
1 million per eye
125:1 convergence into optic nerve
Optic tracts relay into?
Lateral geniculate nuclei of thalamus
A part of each tract goes to the ?
Superior colliculus in the mid brain
After the lateral geniculate nuclei the output goes exclusively to?
Striate Cortex of occipital lobe V1
Colour information is passed onto regions such as?
V4
What is consensual response?
If light shone in eye with optic nerve damage, then that eye wont contract but other will
What happens if there’s a damage to one oculomotor nerve?
No pupil contraction in that eye, but stimulation of either eye will cause contraction in the pupil of second eye
