Vision Flashcards
Hypermetropia
Long sightedness
Eyeball too short
Lens system too weak
Treatment- converging corrective lens
Myotopia
Eyeball too long
Lens system too short
Treatment- diverging correcting lens
Focus of the eye
Carried out by changing shape of the lens (1/3 ray bending)
What is the function of the iris?
it can vary its diameter and therefore retinal intensity
Where is the pigment layer? What is its functions?
Behind retina
absorbs unwanted light
Fovea
What is its function?
small yellow spot on opthalmoscope
-densely packed with cones
-small region in retina that gives the clearest image
What types of photoreceptors exist
Rods- dim light
-A lot more present
Cons- bright light and colour
-fewer
Processing layers of retina
3 direct layers
- receptors
- bipolars
- ganglion cells
2 transverse layers
- horizontal
- amacrine cells
Rhodopsin
- Location
- receptor type
- Mechanism
- rods of the retina -G-protein-coupled receptor (GPCR)
- sensitive to light
- vision in low-light conditions.
Mechanism
- Photon from light hits molecule
- change from cis to trans
- triggers intracellular events
- hyperpolarisation in membrane
Peak spectral sensitivities of human cones
- red cones
- green cones
- blue cones
- rods
Red cones: 560 nm [most]
Green cones: 530
nm
Blue cones: 420 nm [least]
Rods: 500 nm
Red/green colour blindness
X linked
mutation in gene
Blue colour blindness
mutation on blue cone gene
chromosome 7
paired in both sexes
so rarer
Central Achromatopsia
Damage to cortical colour processing areas (V4)
Central Visual Pathway
Left Retina
- temporal field- R LGN
- nasal field- L LGN
Right Retina
- temporal field - L LGN
- nasal field - R LGN
- Optic nerve
- optic chiasma
- optic tract
- LGN
- Optic radiation
- visual cortex in occipital lobe (aka striate cortex)
The Visual Association Cortex is associated with which Broadmann area?
Broadmann Area 18 & 19
The Striate Cortex/Primary Visual Cortex is associated with which Broadmann area?
Broadmann area 17
Name causes of scotoma [3]
- retinal damage
- Lesions in visual cortex
- pressures from tumours restricting structures
Describe the dorsal stream in the cortex. What is it concerned with?
occipital to parietal
- location
- motion
- action
Describe the ventral stream in the cortex. What is it concerned with?
occipital to temporal
- object (and face identity)
- conscious perception
Visual agnosia.
- Pt can’t recognise
- Lesion in ventral stream
Prosopagnosia
Inability to recognise faces
-fusiform gyrus located in temporal lobe
Vestibulo-ocular reflex
stabilizes gaze by countering movement of the head
Optokinetic reflex
stabilizes the image of a moving object on the retina
Pupillary reflex (example of shining light on left eye)
when you shine a light on one way, it will constrict (directly) and so will the other eye (consensual response)
- info travels down optic tract and synapses onto pretectal nuclei projecting to both edinger-westphal nuclei on both sides
- this stimulates the occulomotor nerve to synapse on ciliary ganglion with short ciliary nerve
- causing constriction of iris
In short, why do both eyes constrict when you shine a light onto left retina?
because the information travels down and synapses onto pretectal nuclei which projects to Edinger-Westphal nuclei on both sides. this activates CN3 which synapses with ciliary nerve on ciliary ganglion.
