Visual System
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
Help!
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| Vision/light numbers | show 🗑
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| What parts of the brain are involved in vision processing? | show 🗑
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| What patterns of light can we recognise? | show 🗑
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| show | Illuminance = light from source (lux), luminance = object-reflected light (cd/m2), albedo = reflectance
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| What intensities of light are there? | show 🗑
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| show | Photopic -> daylight/bright light (retinal cones), mesopic -> normal vision (cones/rods), scotopic -> dim light vision (rods)
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| Contrast (relative intensity) equation | show 🗑
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| show | Difference between luminances (reflecting areas)
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| show | Pattern of contrasts independent of ambient illumination -> visual systems extract contrast pattern
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| show | 1 degree = 60 arc mins = 3600 arc seconds -> 300 micrometers on retina
1 radian = 57 degrees
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| What does diffraction limit? | show 🗑
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| show | Angular diameter d = 1.22 lambda/D (pupil aperture)
Smaller aperture -> larger diffraction limit
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| show | Green light (500 nm), smallest pupil diamter (D) = 2mm, angular diameter (d) = 1 arc min
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| What lens aberrations are there? | show 🗑
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| What images would small pupils give you? | show 🗑
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| What images would dilated pupils give you? | show 🗑
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| What refractive errors are there? | show 🗑
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| What is myopia? | show 🗑
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| What is presbyopia? | show 🗑
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| show | 30% population -> lens too thin (smaller refraction)/short eyeball (foci behind retina), corrected w/ converging lens
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| show | Distance 2x as fine as width of pointspread function -> contribute to photoreceptor packing density/size -> pointspread function = 1 arc minute -> fovea -> adj cones separated by 0.5 arc minute (2.3 micrometer)
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| show | Cornea, lens
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| What are the accessory optical structures? | show 🗑
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| Cornea characteristics | show 🗑
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| Lens characteristics | show 🗑
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| show | Lens clouding with age due to xcs UV exposure
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| What is optical power? | show 🗑
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| show | Avascular cornea/lens (aqueous humour supplies metabolites)
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| Aqueous humour characteristics | show 🗑
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| show | Reduction in aqueous humour outflow rate due to damaged optic nerve (increased intraocular Pa) -> determined w/ puff of air at eye and measuring lens deflection
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| What is accommodation? | show 🗑
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| Neurophysiology of accommodation | show 🗑
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| show | Iris has 2 antagonistic smooth muscles under ANS -> sphincter (PNS) -> pupil constriction (blocked by atropine), dilator (SNS) -> pupil dilation
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| What is Argyll-Robertson pupil? | show 🗑
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| show | Furthest from incident light -> remaining layers have visual interneurons -> glare, Muller cells (retinal glial cells) have optical waveguids aiding light transmission through vitreous humour
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| show | 1.5 mm/5 degree diameter -> interneurons displaced to one side reducing light scattering, cone density increases dramatically (rod expense) -> containe blue absorbing macular pigment -> absorb UV wavelengths protectign eye/reduce chromatic aberration
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| show | Central 260 micrometer (1 degree) of fovea w/ highest acuity -> avascular (minimise scattering), completely rod free -> minimum cone spacing of 0.5 arc min (2.3 micrometer) at centre
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| show | Lateral 20 degrees either side of fovea -> peak rod density (same as foveal cones) -> signals summated/pooled reducing spatial acuity -> most sensitive vision under mesopic/scotopic condition
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| show | 5 degrees at optic disc where optic nerve exits retina
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| Optic nerve characteristics | show 🗑
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| Optical imaging methods | show 🗑
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| show | Gives vertical section in intact eye using reflected light to visualise retinal layers -> can detect central serous chorioretinopathy (fluid leakage under retina via epithelial pigment detachment)
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| Scanning laser ophthalmoscope | show 🗑
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Created by:
vykleung
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