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Optical Science 6 > Lec 5: vitreous and retina > Flashcards

Lec 5: vitreous and retina Flashcards

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1
Q

Define the entrance pupil of the eye

A

virtual image of the pupil, in AIR

why is it in air? virtual image looks like its in aqueous, but the real pupil is in aqueous. therefore our virtual image is in air.

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2
Q

define the exit pupil of the eye

A

virtual image of the pupil (made by crystal lens), in vitreous

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3
Q
  1. The vitreous is largely transparent, but some scattering occurs due to fibrous structures (collagen fibers). Scatter is relatively small in young eyes and increases with age as the fibers degenerate.
  2. Scatter in the vitreous is best viewed using special technique (dark-field illumination). However, some scatter can be readily observed in older eyes with a standard ophthalmoscope.
A

human vitreous structure

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4
Q

Deviation of light in multiple directions, as may be produced by particles in the medium through which the light passes.

A

scatter

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5
Q

total transmittance of light through the eye

A

direct + forward scattered

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6
Q

visible wavelength range

A

400-700 nm

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7
Q

when light gets into eye, what percent gets into retina?

A

79%

*of that 79%, some is forward scattered tho

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8
Q

where is there a lot of absorption of uv light (<400 nm) in eye?

A

from anterior surface of lens to posterior surface of lens

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9
Q

above 1200 nm long wave length light (infrared light), where is this absorbed in eye?

A

vitreous and retina

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10
Q

The strong absorption spectra of the cornea and aqueous at certain infrared wavelengths make the anterior of the eye ________ at these wavelength.

A

opaque

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11
Q

The human eye consists largely of water. Water is highly transparent in visible light, but highly absorbent in the ____ at wavelengths above 1.1
microns.

A

infrared

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12
Q

Alien (Spectrum and brightness of their sun could differ from ours.
How would this change the evolutionary development of their eyes?

A
  1. Large optics (eyes) to collect more light.

2. Transparent in the infrared, but opaque at visible wavelengths.

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13
Q

direct transmittance

A

light that forms image on our retina

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14
Q

42% of direct light forms what?

A

retinal image

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15
Q

what amount of light is absorbed, reflected, or backward scattered by ocular tissue?

A

79%

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16
Q

what amount of forward scattered light that reaches the retina & forms a halo?

A

37%

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17
Q

a turbid cornea and crystalline lens that scatters off-axis light onto a foveal image, thus decreasing what?

A

image contrast.

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18
Q

The primary optical effect of ocular scatter is reduced what?

A

contrast of the retinal image

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19
Q

what percent of the incident light is forward scattered by the optics of the eye? Scattering increases with age and with certain types of surgery, e.g., refractive surgery.

A

40%

20
Q

range for uv light

A

200-380 nm

21
Q

what absorbs most of uva light?

A

crystal lens

22
Q

what absorbs uv light <0.3 microns?

what pathology does this cause?

A

cornea; uv keratitis

23
Q

what absorbs uv light b/w 0.3 micron to 0.4 microns? what pathology does this cause?

A

lens; cataracts

24
Q

what pathology is caused b/c uv is reaching our retina?

A

age related maculopathy

25
Q

uvc is absorbed by what?

A

ozone layer

26
Q

uvb is absorbed by what?

A

cornea and lens

27
Q

range for uva?

A

315-380 nm

28
Q

range for uvb

A

280-315 nm

29
Q

uvc range?

A

200-280 nm

30
Q

What percent of uva and uvb reaches the eye?

A

5%

31
Q

UV radiation is most abundant where?

A

whenever there is less atmosphere between you and the sun (e.g. mountain top, low latitudes, sun at zenith)

32
Q

Optical properties of the retina

A
  1. Absorption (blood vessels, macula, photoreceptors, RPE)
  2. Scatter (neural tissue)
  3. Refraction (not really)
  4. Reflection (photoreceptors, RPE, and choriod)
  5. Transmit (neural tissue)
33
Q
  • Thin (>200 μm), transparent
  • little scatter in young, healthy eyes
  • macular pigment absorbs short wavelengths
  • pigment deposits (drusen) common in old age
  • dense capillary vasculature absorbs and scatters light; creates “Purkinje tree”
  • photoreceptors are directional, phototropic
  • spherical shape gives wide field of view, good focus
A

retina

34
Q
  1. Where should the image form in the retina to provide best focus?
A

photoreceptors

*cones and rods capture light

35
Q
  1. How does the retina minimize its own degradation of the retinal image?
    (i. e. before the image is captured by the photoreceptors)
A 
foveal cones are more sensi to scattered light than peripheral ones
1. Homogeneous refractive index
between neural layers
2. At fovea, neural tissue is pushed to
the side.
3. Avascular zone formed at fovea.
36
Q
  1. How do the photoreceptors capture the retinal image? (i.e. what optical properties of the receptors are required?)
A

total internal reflection

37
Q

While this is a strange way to design the retina, it permits what?

A

the RPE and choroid to provide the nutrients necessary to meet the high metabolic demand of the photoreceptors.

38
Q

Unfortunately light passing through these layers can scatter and become problematic depending on the cone size.
Three solutions to minimize this problem are:

A 
1. Homogeneous refractive index
between neural layers
2. At fovea, neural tissue is pushed to
the side.
3. Avascular zone formed at fovea.
39
Q

where are larger cones?

A

in periphery

40
Q

scattered ray enters 3 cones away in fovea. this will do what to the image?

A

degrade image

*fovea cones are more sensitive than peripheral retina

41
Q

where is cone density high?

A

fovea

42
Q

scattered ray enters 3 cones away in peripheral. this will do what to the image?

A

does not degrade image

43
Q

how does light get captured by photoreceptor?

A

total internal reflection
an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary, no light can pass through and all of the light is reflected.

44
Q

Light collection by photoreceptor is dependent on what?

A

on the incident angle

45
Q

Reaction of certain plants and animals to move towards or away from a source of light

A

phototropism

Optical Science 6 (13 decks)

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