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PSYC 367 > L13-L15 (Vision) > Flashcards

L13-L15 (Vision) Flashcards

1
Q

Light

A
  • wave comprising a stream of photons (tiny particles) that each consist of one quantum of energy
  • measured by its wavelength

  • wavelength: distance between peaks of an energy wave
  • wave over space, not time (like sound)
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2
Q

Visible spectrum

A

wavelength determines the color (i.e. hue) perceived

  • wavelengths between 400 nm and 700 nm are visible (nm= 10^-9 m)
  • hue ranges from ROYGBIV (longest to shortest)
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3
Q

2 properties of light intensity

A
  1. wave: height of peaks of an energy wave (amplitude)
  2. particle: number of quanta emitted by a light source or reflected off a surface

intensity (physical property) determines brightness perceived (psychological property)

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4
Q

Which light sources have short vs long wavelengths?

A

different light sources emit energy at different wavelengths
* sunlight has shorter wavelengths (blue)
* lightbulbs have longer wavelengths (yellow)

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5
Q

What happens to light once transmitted?

4 pathways

A
  • transmitted: conveyed from one place (light source) to another (eye), usually with refraction
  • absorbed: medium heats up and light not transmitted
  • reflected: redirected back toward its origin
  • diffracted: dispersed in an irregular fashion by dust or water particles in the air
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6
Q

How is the color of a solid object vs transluscent object determined?

A
  • color of solid object depends on wavelengths reflected off the object back to the eye
  • color of transluscent object depends on wavelengths transmitted through the object to the eye
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7
Q

Refraction

usually happens with transmission

A

change in direction (or bending) of light ray passing from one transmitting medium into another

  • depends on wavelength
  • based on Newton’s experiment, short wavelengths are refracted the most and long are refracted the least
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8
Q

Anatomy of the human eye

yellow

A
  • cornea: clear outer layer that is very sensitive to touch
  • iris: outer pigmented layer and inner layer of blood vessels that controls the size of the pupil
  • pupil: hole in iris where light enters
  • ciliary muscles: control shape of lens
  • sclera: protective white outer surface
  • aqueous humor: fluid in anterior chamber that is continually replenished
  • vitreous humor: fluid in posterior chamber than transform into floaters

acqueous humor supplies oxygen and nutrients to, and removes waste from the cornea and lens

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9
Q

Anatomy of the eye

blue

A
  • retina: inner layer that detects light and transduces light energy into neural signals
  • choroid: blood vessels that nourish retina
  • macula: yellow pigmented spot in retina
  • fovea: pit in macula with best vision
  • optic disk: axons of retinal neurons form the optic nerve (II)

photoreceptors in retina absorb light

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10
Q

Optical vs neural apparatus in eye

A
  • optical: cornea, lens, pupil (in iris), aqueous and vitreous humor
  • neural: retina
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11
Q

What does the sharpness of an image depend on?

image is focused on retina!

A

ability of cornea, lens, aqueous and vitreous humors to refract light

light is transmitted through cornea, lens, and aqueous and vitreous humors

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12
Q

Accommodation

A

process by which the eye changes its focus (and refractive power) by changing the shape of the lens

whens ciliary muscle contracts, fatter lens increases the optical power of the eye, causing light to bend more and bringing images of near objects into focus

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13
Q

Cataract

A
  • opacity of the crystalline lens of the eye that interferes with retinal image quality
  • can be congenital and treated by surgical removal and replacement of lens
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14
Q

2 kinds of pupil reflexes

A
  1. direct light reflex: shining a light into one eye causes the pupil of that eye contract
  2. consensual light reflex: shining a light into one eye causes the pupil of the other eye to contract

size of pupil depends on the amount of light

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15
Q

2 kinds of abnormal reflexes that indicate brain injury

oculomotor and optic nerves

A
  1. no direct or consensual reflex in the right eye indicates problem with oculomotor nerve controlling right pupil
  2. consensual but no direct reflex in right eye, direct but no consensual reflex in left eye indicates problems with optic nerve in right eye
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16
Q

What causes pupil size ranges to contract and dilate?

A
  • contracts due to increased amount of light
  • dilates for emotionally arousing pictures (or anything affecting sympathetic nervous system)

  • pupil size ranges from 2-8 mm
  • pupil responses similar to skin conductance changes, involves autonomic nervous system
17
Q

Depth of field

A
  • range of distances over which objects are in focus
  • larger (more objects in focus) with small pupil
18
Q

3 refractive errors

A
  1. emmetropia: length of eyeball matches the power of the optical elements and images are focused exactly in back of retina
  2. myopia: eyeball too long or optics too strong (too much refraction) and distant objects are focused in front of retina
  3. hyperopia: eyeball too short or optics too weak and images are focused behind retina

optical elements: cornea, lens, acqueous and vitreous humors

19
Q

Changes in lens in myopia (nearsightedness)

A
  • lens too fat, bringing only near objects into focus
  • can’t relax lens enough (i.e. unaccommodate) to bring distant objects into focus

corrected with negative, concave lens

20
Q

Onset and causes of myopia

A
  • usually develops later in childhood and increases throughout adolescence
  • tends to run in families (genetic) but incidence is increasing due to environmental factors

e.g. near-work (like reading), especially under low illumination, causes eyeball to continue to grow

21
Q

Protective mechanisms for myopia onset in children

A

outdoor activity like light-induced retinal dopamine and 2 hrs/day of sunlight

22
Q

What slows myopia progression?

A
  • keeping reading distance (>20 cm) of books, phones, tablets
  • low-dose atropine eye drops
  • overnight orthokeratotic lenses (though not recommended due to high risk of severe eye infections)
23
Q

Changes in lens in hyperopia (farsightedness)

A
  • lens too thin, making it easier to see distant objects
  • positive, convex lens brings both near and distant objects into focus

present in most newborns and many become emmetropic as eyeball grows

24
Q

Astigmatism

A
  • visual distortion produced by nonspherical cornea
  • cause unknown but has genetic and environmental factors

causes one line to look blacker

25
Q

How is astigmatism corrected?

A
  • cylindrical lens with 2 focal points to provide different optical power for 2 axes/orientations
  • rigid contact lenses for myopia or hyperopia

also corrected in both the top and bottom part of bifocals

26
Q

Presbyopia

A

normal part of aging wherein ability to accomodate is lost due to hardening and loss of elasticity of lens

usually begins in mid 40s

  • accomodative amplitude (i.e. maximum increase in optical power) decreases with age
  • corrected with positive, convex lens (reading glasses)
27
Q

Near point

A

closest distance at which objects can be brought into focus

changes with age

~6.7 cm in young emmetropic eyes with an optical power of 15 D (dioptres)

28
Q

What are bifocals?

glasses

A
  • near vision correction (for presbyopia) on the bottom to compensate for loss of accomodation
  • distance vision correction in the rest of the lens (for myopia or hyperopia) to compensate for refractive errors due to eyeball length

astigmatism is corrected in both the top and bottom part of lenses

29
Q

Optical coherence tomography (OCT)

A

a non-invasive imaging technique to see the layers of the retina in a living human eye

30
Q

Arrangement of photoreceptors in the fovea

A
  • center: only densely-packed cones
  • away from fovea: more rods, fewer cones, less dense

  • most neurons pushed to the side and light passes through a thinner layer
  • no photoreceptors in optic disk!
31
Q

Duplex vision

A
  1. scotopic: rod-mediated vision in dim light
  2. photopic: cone-mediated vision in bright light

cones are less sensitive than rods in dim light and rod response saturates in bright light

32
Q

What are the seven layers of the retina?

A
  1. photoreceptor layer
  2. outer nuclear layer
  3. outer plexiform layer
  4. inner nuclear layer
  5. inner plexiform layer
  6. ganglion cell layer
  7. nerve fiber layer

  1. inner and outer segments of rods and cones
  2. nuclei of rods and cones
  3. synaptic terminals of rods and cones; dendrites of bipolar and horizontal cells
  4. nuclei of bipolar, horizontal, amacrine cells
  5. synapses of bipolar cells with amacrine and retinal ganglion cells
  6. nuclei of retinal ganglion cells
  7. axons of retinal ganglion cells

PSYC 367 (7 decks)

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