EXAM 3 Sensation and Perception Vision I Light Eye Anatomy Optics Introduction to the Retina 1 What does the visual spectrum refer to Even if we can t see it is there other electromagnetic radiation that we somehow respond to Know an example of an animal that uses more of the electromagnetic spectrum Visual Spectrum 380 760 nm o We are sensitive to only a limited portion of the spectrum of light UV we don t see but tissue damage sunburn Rattlesnakes hummingbirds bumblebees are able to use more of the electromagnetic spectrum 2 FYI of photons perception of intensity wavelength perception of color 3 Slide 6 know the terms in red Radiance energy from source intensity of a light beam the sun radiates light Illuminance energy source from source to object the amount of light falling onto patch of unit surface area the sun illuminates the Earth o When the light hits the surface it can be reflected absorbed or transmitted If a surface looks lighter it is reflecting most of the light If a surface looks dark it is absorbing most of the light If a transmitted some is refracted bent Such as when light goes into through the water or the eyeball 4 Know the parts of the eye Be able to label them on a picture and know what they each do Cornea o Transparent tissue covering the front of the eye o Continuous with sclera protective coating around back 5 6 of eye o Light is transmitted and refracted through this o No blood vessels o Nerve endings to detect touch and to force eye to close and produce tears if the cornea is scratched to preserve transparency What nerves you ask Afferent branch is trigeminal v efferent is facial VII Aqueous Humor o Fluid derived from blood o Just behind cornea o Supplies oxygen and nutrients to cornea and lens o Removes waste from cornea and lens o Helps maintain shape of eye and intraocular pressure too much production or too little drainage in glaucoma Crystalline Lens Lens o Transparent tissue o Bends light that is passing through the eye to focus image on retina o Accommodation near far focus o How does it bend light o By bending itself Ciliary muscles control its curvature o Circular band of muscles dilator sphincter that controls the size of the pupil therefore controls light entry o Hole in the center of the iris where light passes through Iris Pupil o Size of pupil dilated or constricted determines how much light can pass Choroid o Layer of blood vessels providing nutrition for the eye o Heavily pigmented high melanocyte content so absorbs extraneous light entering eye this reduces reflection within eye would blur image o Attached to sclera Vitreus Humor o Between lens and retina o 80 of internal volume of eye o Clear jelly like fluid o Refracts light o Maintains shape of eye o Floaters bits of biodebris that drift around in vitreus you see them maybe in bright light Retina o Layer of tissue on back portion of eye o Like an outgrowth of the brain same embryonic tissue o Nerve cells and photoreceptors rods and cones to absorb light photons and transduce it to neural activity o Fovea point of central focus 5 What is the pupillary light reflex What cranial nerves are involved Why does red eye occur in photographs Pupillary light reflex o AKA Whytt s reflex Immediate constriction of pupil in response to bright light CNs II and III next slide o Red eye dim light pupil dilated too much light in reflected back from fundus through choroid latter gives reflection red appearance 6 What is accommodation how is it accomplished What shape do you need your lens flat or bulging to see close by What about to see far away What is presbyopia what causes it Accommodation o So as opposed to other parts of the eye the refractive power of the lens is dynamic o Ability to accommodate decreases with age Presbyopia to focus on things within arm s reach By 40 50 years old cant accommodate enough Why Lens becomes harder and capsule surrounding it loses elasticity Like camera lens move forward to focus on nearby object back to focus on distant object o Some vertebrates like fish accommodate by moving lens in relation to retina o In order to see far away Ciliary muscle is relaxed Zonules are stretched Lens is flat Focus on distance o In order to see close by Ciliary muscle contracts in Zonules are relaxed less tension Lens buldges Focus on close objects 7 What are cataracts What causes them How do they affect vision Opacities in the lens caused by irregularity in the crystallins o Crystallins densely and regularly packed proteins that make up the lens and whose organization dense and regular gives the lens its translucence Different types different locations which of the many layers of the lens Interfere with vision because absorb and scatter more light than the normal lens Causes risk factors congential rare age related usually after 50 in the most people after 70 diabetes being struck by lightning penetrating or non penetrating eye trauma sun exposure else Treatment o Removal of most of the lens except for the most posterior portion which connects to the zonules Then put in a prosthetic lens o Congenital cataracts must be removed early best outcome if done in 1st 4 6 wks of life Lens removed completely Intraocular lens put in or glasses if in both eyes Increased risk of glaucoma after surgery in very young infants 8 What are emmetriopic hyperopia myopia Emmetriopia perfectly matched to the length of the eyeball Nearsightedness Myopia no refractive error because the refractive power of the eye is o Eyeball is too long for refractive power of eye so focus image in front of retina instead of on it star looks like a blur o Correct with negative minus concave lenses which diverge the rays before they enter the eye Hyperopia Farsightedness o Eyeball is too short for refractive power of eyes so focus behind retina again star looks like a blur o If young can correct accommodating o Correct with plus convex lenses to converge rays before they enter the eye o Most newborns are hyperopic because optical components of eyes are well developed at birth compared with length of eyeballs o 9 What is astigmatism Occurs when cornea isn t spherical curved more steeply in one direction than the other like going from a basketball to a football Vertical lines might be focused just in front of retina and horizontal lines might be focused just behind retina or vice versa In image to right one or more of the lines will appear out of focus others will be in focus if have uncorrected astigmatism 10 What is the
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