Opthamology 1 - Eye and Vision (special senses) Flashcards
What are the connections of the eyeball to the brain?
- Optic nerve
- Chiasm
- Optic tract
- LGN (lateral geniculate nucleus)
- Radiation
What is presbyopia?
When lens inside eye looses ability to see things close by
What is the most common from of refractive error?
Presbyopia
How does the lens focus on near objects?
Thickens
What is myopia commonly known as?
Short sightedness
What is hypermetropia commonly known as?
Long sightedness
What are normal sized eyes called with normal refraction?
Emmetropic - emmo
Are myopic eyes usually smaller or larger than emmotropic/normal eyes?
Larger (nearsightedness)
What lenses prescribed to help myopia/nearsightedness?
Concave
Are hyperopic eyes usually smaller or larger than emmotropic/normal eyes?
Smaller
What type of lenses are prescribed to help hyperopic eyes/farsighted?
Convex
What are the cells which respond to light on the retina?
Photoreceptors
What is the optic nerve made up of?
Axons of the ganglion cells of the retina
What is the central part of the retina called?
The macula - very centre is called the fovea
Where are more rods found?
Peripherally
Where are cones found generally?
Centrally - concentrated in macula highest density in fovea
How many rods are found in the retina?
120 million
How many cones are found in the retina?
6 million
How do rods and cones compare when converging to ganglion cells?
Rods
- High convergence to ganglion cells
Cones
- Low convergence to ganglion cells
How many types of rods are there?
1 type (vision in greyscale)
What are the different types of cones?
3 types
- Red
- Blue
- Green
How much more sensitve are rods compared with cones?
30x more
Do rods and cones have broad spectral sensitivity?
- Rods have broad spectral sensitivity
- Cones have narrow spectral sensitivity
What is the blind dpot of the eye due to?
Optic disk (aka optic nerve head)
What cells are more sensitive rods or cones?
Rod cells
What do the axons of the ganglions in the retina run along?
Superficial surface of the retina and exit at the optic nerve
What is the neuroretinal rim?
- Tissue between the border of the cup and the disk
- Pink/orange
- Made up of axons of the ganglion cells
What is the cup?
Space within the centre of the optic nerve can see sclera through it
- Blood vessels enter and exit through here
What is the sclera?
Tough collaginus coating of the eyeball
What does it mean if the margin of the optic nerve is not distinct and clear?
- Swollen optic nerve
- Disease such as raised intracranial pressure
WHat hapens if the cup is bigger?
- Neuroretinal rim gets thinner
- Losing axons from ganglion cells
- May represent glaucoma
What is the main cause of irresversible sight loss in the world?
Glaucoma
Where do both optic nerves join?
Optic chiasm
What do optic nerve fibres join after optic chiasm?
Optic tracts
What axons cross over to the other side of the brain at the optic chiasm?
Axons from the medial side of the retina
Information from the left visual field is processed where?
The right side of the brain
What is bitemporal hemianopia?
Vision is missing in the outer half of both the right and left visual field
- Chaism damage
If you have damage to the right optic nerve where will vision be lost?
The right eye
If you damage right occipital lobe where will vision be lost?
Left visual field (left hemianopia)
If you daamage the left optic tract where will vision be lost?
Right visual field (right hemianopia)
What is a quadrantanopia?
Loss of vision in one quarter of the visual field
- Due to lesion in temporal, parietal or occipital lobe
- Due to fibres in the optic tract seperating as it travels to the primary visual cortex
Information in the upper part of the visual world project where?
Lower part of the retina and therefore lower part of the occipita lobe via temporal lobe
Information from the lower part of the visual world projects where?
Upper part of the retina and therefore lower part of the occipital lobe via parietal lobe
What area is often damaged in premature neonates?
Optic tract through the pariatal lobe causing an inferior quadrantanopia
What are the 2 seperate functional streams of vision?
- Where? stream (dorsal stream) via parietal lobes
- What? stream (ventral stream) via temporal lobes
What lobe creates a functional plan based on visual information?
Frontal
What lobe of the brain stores visual memory?
Temporal lobe
Dorsal stream dysfunction is usually a result of damage to what part of the brain?
Posterior parietal lobe damage
What is the Ebbinghaus Illusion?
Optical illusion of relative size perception
What lobe of the brain hosts the primary vision cortex?
Occipital lobe
At what age does a babies vision become adult-like?
18 months - will continue to mature and develop and leave ‘plastic’ period after 8 years
What is periventricular leukomalacia?
Damage and holes in white matter of the brain around ventricles due to ischaemic damage
What are the features of dorsal stream dysfunction?
- Difficulty in seeing and understanding complex visual images
What is simultanagnosia?
- Inability to perceive more than a single object at a time
- Result of parietal lobe damage
What is achromatopsia?
- Inability to see colour
Bilateral anterior occipital brain damage
What lobe of the brain serves the function of attention?
Parietal
