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Ocular Physiology #2 > Retina > Flashcards

Retina Flashcards

1
Q

how much of the eye is retina

A

extends over the posterior 2/3 of globe

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2
Q

what are the boundaries of the retina

A

internally bound by the vitreous and externally connected to Bruch’s membrane

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3
Q

how many layers thick is the retina

A

10

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4
Q

what color is a normal retina

A

reddish because of purple rhodopsin (thin transparent membrane)

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5
Q

what happens to the retina with light exposure

A

bleaches

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6
Q

when does the retina turn gray/opacify

A

1 hr after death

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7
Q

what are the two chief retinal functions

A

detecting light and movement (rods) and color and form vision (cones)

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8
Q

what are rods and cones names based on

A

the appearance of their outer segments

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9
Q

where is the retina thinest

A

centrally and peripherally

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10
Q

what is the fundus oculi

A

the internal background of the eye, orange-red color secondary to choroid and RPE

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11
Q

what does the fundus look like in fair and darker subjects

A

lighter in fair and darker/grayish fundi

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12
Q

what does the fundus look like in albino patients

A

you can see the choroidal vessels through the retina and the white scleral tissue

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13
Q

why is the fundus of albino patients transparent

A

they are almost devoid of pigment (extremely photophobic)

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14
Q

where is the optic nerve located

A

3mm medially to and slightly above the posterior pole

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15
Q

what is the blind spot

A

the optic disc is devoid of photoreceptors- its projection into space produces the blind spot

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16
Q

where is the fovea centralis located

A

temporal to and below the posterior pole (1-2mm diameter)

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17
Q

what is the fovea centralis

A

retinal thinning produces a shallow depression in the surface where the nerve elements are heaped to form Henle’s layer

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18
Q

what is the foveola

A

the 0.35mm within the fovea, only has CONES

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19
Q

what is the macula lutea

A

the yellow spot around the fovea centralis, yellow pigment (xanthophyll) found here

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20
Q

what are the 4 areas of the fovea centralis

A

foveola, fovea, parafoveal area, and periforveal area

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21
Q

what is the ora serrata

A

it separates the neural part of the retinal periphery from the ciliary body

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22
Q

where is the ora serrata

A

8.5mm behind the limbus and 6mm in front of the equator

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23
Q

where is a common spot for retinal detachments

A

in the ora serrata- the vitreous is firmly attached here

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24
Q

what do the arteries and veins look like in the retina

A

the arteries are thinner and lighter, veins are wider and darker

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25
Q

are there anastomoses in the retinal arteries and veins

A

no

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26
Q

what are the 4 subdivision regions of the retina

A

pigment epithelial layer, photoreceptor layer, intermediate cell layer, ganglion cell layer

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27
Q

what is the pigment epithelial layer (RPE) connected to

A

Bruch’s membrane

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28
Q

what are the 5 functions of the RPE

A
  1. absorption of light and removal of heat
  2. captures excessive and stray light- projects receptors
  3. provides nutrients and O2 to photoreceptors
  4. reservoirs of useful substances (vitamin A)
  5. phagocytotic activity of shed discs
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29
Q

does the RPE layer have mitosis

A

no, neighboring cells occupy space after cells die

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30
Q

how many cells is each pigment epithelium cells in contact with

A

up to 45 photoreceptors

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31
Q

what is the connection between the photoreceptor layer and the RPE

A

no real connection (only adjacent to each other)

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32
Q

what are photoreceptors

A

sensory cells: transform light into electrical energy by chemical processes

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33
Q

what is the arrangement of the photoreceptors

A

palisade arrangement (picket-fence) being held in position by the external limiting membrane

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34
Q

what do rods look like

A

long (40-60 microns), slender (2 microns)

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35
Q

what is the outer segment contain in a rod

A

rhodopsin- about 600-1000 loosely stacked disc units (lamellae)

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36
Q

what is the rate of formation for the lamellae in the rod

A

1-5 per hour at the bottom of the segment

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37
Q

which lamellae get sloughed in a rod

A

a group of 30 from the top of the segment

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38
Q

when does sloughing occur the rod lamellae

A

in the morning or after long dark periods

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39
Q

when can rod lamellae be completely renewed

A

over 1-2 weeks

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40
Q

do rods have a high or low sensitivity to light

A

a high sensitivity (sensation is the same for all wavelengths of light)

41
Q

how many rods go to one bipolar cell

A

several (15-30) producing an impulse convergence

42
Q

where are the cones more cylindrical shaped

A

in the fovea-due to packing so many in a small space

43
Q

what is the cone pigment

A

iodopsin

44
Q

what are the outer segment lamellae attached to in cones

A

the cell membrane

45
Q

do cones react to large or small amounts of light

A

large (why colors are not seen during night-dark vision)

46
Q

when are the discs of the cones shed

A

periodically and mainly during the end of the day

47
Q

what are the 3 cone photopigment categories (each having a distinct spectral sensitivity)

A

short (blue), medium (green), and long (red) wavelengths

48
Q

what is rhodopsin

A

an intrinsic membrane protein, found in discs and some extent plasma membrane of rod outer segment

49
Q

where is rhodopsin more prevalent

A

in the discs

50
Q

what is formed after light hits rhodopsin

A

Bathorohdpsion forms

51
Q

what is formed following metarhodopsin

A

all trans retinal and opsin are produced

52
Q

what are the two steps to regenerate rhodopsin from metarhodopsin

A

all trans retinal is isomerised to 11-cis retinal isomerase and then opsin combines with 11-cis retinal to make rhodopsin

53
Q

what is Tay-Sachs ganglioside (GM2)

A

a genetic retinal disease, where partially degraded gangliosides accumulate in neural, ocular and other tissues

54
Q

what is Tay-Sachs ganglioside a result of

A

hexaminodase A deficiency (the enzyme that normally catalyzes the breakdown of ganglioside molecules)

55
Q

in Tay-Sachs gangliodie, what appears on the retina as a result of the accumulation of GM2 and ganglion cells degenerate

A

a cherry red spot in the macular region

56
Q

what symptoms occur with Tay-Sachs ganglioside

A

blindness occurs early and failure to develop motor/mental capacities (resulting in death age 3-6)

57
Q

what forms Rhodopsin

A

11-cis vitamin A aldehyde (retinal) and opsin

58
Q

what class of lipids does vitamin A belong to

A

the isoprenoid class

59
Q

what is the role of retinyl ester

A

storage

60
Q

what is the role of retinol

A

transport and hormone to control certain kinds of protein synthesis

61
Q

what is the role of retinal

A

visual transduction

62
Q

what is the role of retinoic acid

A

synthesis- formation of glycoproteins and the maturation of epithelial cells (corneal epithelia)

63
Q

what are the 4 chemical forms of vitamin A

A

retinyl ester, retinol, retinal, and retinoic acid

64
Q

what are 2 dietary sources of vitamin A

A

beta-carotene (yellow vegetables: carrots and sweet potatoes) and retinyl esters (animal sources)

65
Q

what are both sources of vitamin A converted to in the gut

A

vitamin A alcohol (retinol), then it is re-esterified and incorporated into chylomicra for liver transport

66
Q

what two proteins does vitamin A (retinal) bind to before mobilizing

A

retinol binding protein (RBP) inside the cell and prealbumin (PA) in the bloodstream

67
Q

after vitamin A (retinal) is bound to two proteins where is it transported to

A

through the blood stream to its target cells: retina and corneal epithelium

68
Q

what is the first sign of a vitamin A deficiency

A

Nyctalopia (loss of night vision)

69
Q

what is follows nyctalopia

A

xerophthalmia (dry eyes, hardening of corneal conjunctival epithelium and loss of conjunctival secretions)

70
Q

what is the last stage of a vitamin A deficiency

A

keratomalacia (degeneration of the corneal epithelium, could cause corneal perforation

71
Q

what are some symptoms of vitamin A excess

A

abdominal pain, blurred vision, drowsiness, headache, irritability, nausea, and vomiting

72
Q

what are the 2 causes of excess vitamin A

A

increased gluconeogenesis and protein turnover (converts the protein into glucose)

73
Q

what type of connection do cones make with bipolar cells

A

a direct synapse, fewer cones are connected to a single bipolar cell

74
Q

which type of cell, rods or cones, provide more localized information

A

cones, they have fewer cells connected to a bipolar cells

75
Q

how many rods do we have

A

110-125 million

76
Q

how many cones do we have

A

6.5 million

77
Q

how many rods are in the central fovea

A

0

78
Q

how many cones are in the central fovea

A

147,000 cones/mm2

79
Q

how many rods are 5-6mm from the fovea

A

160,000 rods/mm2

80
Q

how many cones are 10mm from the fovea

A

4,000 cones/mm2

81
Q

what is the outer limiting membrane

A

a support network to hold the photoreceptors together, condensation of cytoplasm (not a real membrane)

82
Q

what does the outer plexiform layer consist of

A

photoreceptor axons, synapses with bipolar cell dendrites, and connections between horizontal cells and photoreceptor synapses

83
Q

what 5 cell bodies are in the inner nuclear layer

A

bipolar cells, horizontal cells, amacrine cells, interplexiform cells, and mueller’s connective fibers

84
Q

what is the ganglion cell layer

A

formed by the bodies of the cells found in the inner nuclear layer

85
Q

how deep is the ganglion cell layer

A

about 10 cells deep at the macula and only one cell deep in the periphery

86
Q

what are the 3 types of ganglion cells

A

magno cells (motion), parvo cells, and konio cells (blue-yellow)

87
Q

which ganglion cell is most abundant

A

parvo cells

88
Q

what is in the nerve fiber layer

A

ganglion cell axons- carrying nervous impulses via the optic nerve to the lateral geniculate nucleus

89
Q

what envelopes the nerve fiber layer fibers

A

extensions of Mueller’s fibers and astrocytes

90
Q

what are 2 retinal glial cells

A

astrocytes and microglia

91
Q

where are astrocytes found in the retina

A

the ganglion and nerve fiber layer (short and long projections extending in all directions)

92
Q

what do the astrocyte cells promote

A

movement from and to the vascular system (nourishment function)

93
Q

what are microglia

A

small connective cells, few present in healthy tissues

94
Q

what do microglia do

A

proliferate for phagocytosis where damage is present

95
Q

what is the main arterial supply to the retina

A

central retinal artery

96
Q

what happens to the central retinal artery at the optic disc

A

the main retinal vessels divide into superior and inferior branches and those divide into nasal and temporal branches

97
Q

where is the capillary network in the retina

A

densest near the macula and absent in the fovea (lacking in a small area behind the ora serrata)

98
Q

what supplies the fovea with blood

A

diffusion will carry nutrients to the fovea (the choroidal layer also supplies the fovea)

99
Q

what is the venous supply to the retina

A

central retinal vein- exits at the optic disc

Ocular Physiology #2 (7 decks)

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