EXAM 3: Sensation and PerceptionVision I – Light, Eye Anatomy, Optics, Introduction to the Retina1. 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 Spectrumo We are sensitive to only a limited portion of the spectrum of light 380-760 nm- UV: we don’t see, but tissue damage (sunburn)- Rattlesnakes, hummingbirds, bumblebees are able to use more of the electromagnetic spectrum2. 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 fallingonto 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 eyeball4. Know the parts of the eye. Be able to label them on a picture and know what they each do.--- Corneao Transparent tissue covering the front of the eyeo Continuous with sclera (protective coating around back 5/6 of eye)o Light is transmitted and refracted through thiso No blood vesselso 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 Humoro Fluid derived from bloodo Just behind corneao Supplies oxygen and nutrients to cornea and lenso Removes waste from cornea and lenso Helps maintain shape of eye and intraocular pressure (too much production or too little drainage in glaucoma)- Crystalline Lens (Lens)o Transparent tissueo 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- Iriso Circular band of muscles (dilator, sphincter) that controls the size of the pupil, therefore controls light entry- Pupilo Hole in the center of the iris where light passes througho Size of pupil (dilated or constricted) determines how much light can pass- Choroido Layer of blood vessels providing nutrition for the eyeo Heavily pigmented (high melanocyte content) so absorbs extraneouslight entering eye…this reduces reflection within eye (would blur image)o Attached to sclera- Vitreus Humoro Between lens and retinao 80% of internal volume of eyeo Clear, jelly-like fluido Refracts lighto Maintains shape of eyeo “Floaters”: bits of biodebris that drift around in vitreus (you see them maybe in bright light)- Retinao Layer of tissue on back portion of eyeo 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 activityo Fovea: point of central focus5. What is the pupillary light reflex? What cranial nerves are involved? Why does “red eye” occur in photographs?- Pupillary light reflexo 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?- Accommodationo So as opposed to other parts of the eye, the refractive power of the lens is dynamico Ability to accommodate decreases with age Presbyopia: By 40-50 years old, cant accommodate enough to focus on things within arm’s reach Why? Lens becomes harder and capsule surrounding it loseselasticity Like camera lens (move forward to focus on nearby object; back to focus on distant objecto Some vertebrates, like fish, accommodate by moving lens in relation to retinao In order to see far away: Ciliary muscle is relaxed. Zonules are stretched. Lens is flat. Focus on distanceo 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 crystallinso 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?- Treatmento Removal of most of the lens except for the most posterior portion, which connects to the zonules. Then put in a prosthetic lenso Congenital cataracts must be removed early (best outcome if done in1st 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 infants8. What are emmetriopic, hyperopia & myopia?- Emmetriopia: no refractive error, because the refractive power of the eye is perfectly matched to the length of the eyeball- Myopia: Nearsightednesso Eyeball is too long for refractive power of eye, so focus image in frontof retina instead of on it…star looks like a bluro Correct with negative (minus; concave) lenses which diverge the rays before they enter the eye- Hyperopia: Farsightednesso Eyeball is too short for refractive power of eyes, so focus behind retina…again star looks like a bluro If young, can correct accommodatingo Correct with plus (convex) lenses to converge rays before they enter the eyeo Most newborns are hyperopic because optical components of eyes are well-developed at birth compared with length of eyeballso9. 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
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