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29 Cards in this Set
- Front
- Back
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The eye is enclosed by 3 layers |
1. sclera/cornea (outermost) 2. choroid/ciliary body (middle) 3. retina (innermost) |
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The eye consists of 3 fluid-filled cavities: |
1. posterior cavity: - larger cavity b/w lens and retina - contains vitreous humour - maintains shape of eye and transmits light onto retina 2. anterior cavity - contains aqueous humour - b/w cornea and lens - carries nutrients for cornea and lens |
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Aqueous humor is produce by and drained by? |
produces by: capillary network within ciliary body drained by: canal of schlemm |
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The iris contains 2 sets of smooth muscle networks |
1. circular (constrictor) muscle
2. radial (dilator) muscle |
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light is a form of
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electromagnetic radiation |
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light rays slow down and change course in a |
dense medium |
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What 2 structures are most important in eye's refractive ability?
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1. cornea - refractive ability remains constant because curvature never changes 2. lens - refractive ability can be adjusted by changing curvature as needed for near or far vision |
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Define accommodation. How is it accomplished? |
ability to adjust the strength and shape of the lens - it is accomplished by action of the ciliary body (muscle) and suspensory ligaments |
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What are the disorders of accommodation? (4)
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1. presbyopia: age related reduction of accommodative ability 2. emmetropia: process by which strength of lens is increased by accomm. to bring a near source into focus 3. myopia (nearsightedness): person can see near better than far 4. hyperopia (farsightedness): person can see better far than near |
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Someone with myopia (3) |
- eyeball is too long of lens is too strong - far source focused in front of retina - corrected with concave lens |
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People with hyperopia: (3) |
- eyeball too short or lens too weak - near source focused behind retina - can be corrected with convex lens |
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Accommodation for far vision |
- ciliary muscle is relaced causing suspensory ligaments to be taut - this makes the lens flat/weak |
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Accomodation for near vision |
- ciliary muscle is contracted causing slackened suspensory ligaments - this makes the lens rounded and stronger |
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What portion of the eye is actually an extension of the CNS? |
the retina |
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Neural portion of the retina consists of 3 layers of excitable cells: |
1. rods & cones (outermost) 2. bipolar cells (middle) 3. ganglion cells (inner) |
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Axons of ganglion cells join to form |
the optic nerve |
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Fovea(3) |
- exact center at back of retina - point of most distinct vision - contains only cones |
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Macula lutea (2) |
- area immediately surrounding fovea - fairly high acuity |
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Macular degeneration (2)
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- leading cause of blindness in western hem - doughnut vision |
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Photoreceptors consist of 3 parts |
1. outersegment: detects light stimulus 2. inner segment: contains metabolic machinery of cell 3. synaptic terminal: transmits signal generated in photorecptor to next cells in visual pathway |
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Photopigments consist of 2 components
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1. opsin: protein that is integral part of disc membrane 2. retinene: derivative of Vitamin A - light-absorbing part of photopigment |
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Rod photopigment |
rhodopsin - absorbs/detects light intensities - proves vision only in shades of gray by detecting intensities |
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Cone photopigments |
- respond to various wavelengths of light - make colour vision possible - 3 pigments (red, green,blue) |
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Rods 1. how many 2. sensitivity 3. acuity 4. night or day vision 5. convergence in retinal pathways 6. where abundant |
1. 100 milion per retina 2. high sensitivity 3. low acuity 4. night vision 5. much convergence in pathways 6. numerous in periphery |
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Cones 1. how many 2. sensitivity 3. acuity 4. night or day vision 5. convergence in retinal pathways 6. where abundant |
1. 3 mill per retina 2. low sensitivity 3. high acuity 4. day vision 5. little convergence in pathways 5. concentrates in fovea/macula lutea |
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Dark adaption (gradually distinguishing objects as you enter the dark) is due to |
regeneration of rod pigments that had been broken down by previous light exposure |
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Light adaption (gradually distinguish objects as you enter area with more light) is du to |
rapid breakdown of cone pigments |
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An object perceived as blue |
does not stimualte red or green cones bu excites blue cone maximally |
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Neural pathways of vision |
1. light
2. photoreceptors 3. rods and cones 4. occipital lobe of cerebral cortex 5. vision perception |
