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Microanatomy > MA7 - The Eye > Flashcards

MA7 - The Eye Flashcards

1
Q

What is the limbus?

A

the site where the sclera and cornea merge

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2
Q

Loss of rods and cones leads to

A

loss of rods = night blindness

loss of cones = legal blindness

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3
Q

In which layer(s) are amacrine cells found?

A

cell body in inner nuclear layer

extends into inner plexiform layer

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4
Q

What structures are found in the ganglion cell layer?

A

cell bodies of ganglion cell neurons

specialized photosensitive cells (not rods and cones) that mediate circadian rhythms

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5
Q

Where does light enter the eye?

A

cornea

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6
Q

The corneoslcera is comprised of

A

cornea

sclera

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7
Q

What are the four functions of the cornea?

A

protection

structural support

filtration of undesirable wavelengths

focus image on retina

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8
Q

What structures are found in the nerve fiber layer?

A

axons of ganglion cells

majority of retinal microvasculature

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9
Q

Describe the constrictor pupillae.

A

arrayed circumferentially

causes pupil to become smaller when it contracts

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10
Q

What are bipolar cells?

A

interneurons that transmit signals from outer plexiform to inner plexiform layer

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11
Q

What is the significance of the tight junctions found in the outer limiting membrane?

A

contribute to the blood-retinal barrier

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12
Q

What are the three functions of the retina?

A

photoreception of images

transmission of images to optic lobe of brain

prevent backscatter of light

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13
Q

What structure connects the anterior and posterior chambers?

A

pupil

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14
Q

What is the function of ciliary processes?

A

provide attachment for zonules (inner epithelial cells)

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15
Q

What is the function of the lens capsule?

A

isolates lens from aqueous humor of posterior chamber

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16
Q

What kind of eptihelium is the corneal endothelium?

A

simple squamous

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17
Q

Describe the innervation and vasculature associated with the fovea. (2)

A

nerves servicing photoreceptors in fovea are distributed radially to fovea, so no nerves directly inside

no retinal blood vessels, so all support comes from choroid

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18
Q

Describe lens fibers.

A

post-mitotic and anuclear long, thin cells that span entire width of lens

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19
Q

Define photorefractive keratectomy (PRK). (3)

A

laser to correct mild-moderate myopia, hyperopia, and astigmatism

removal of corneal epithelium and then usage of lasers to reshape corneal stroma

replacement epithelium grows out from limbus

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20
Q

Differentiate between rods (3) and cones.

A

rods = more numerous than cones; absent in fovea; use rhodopsin

cones = 3 types, each of which produces a different iodopsin (blue, green, or red); concentrated in macula; only photoreceptor found in fovea

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21
Q

Ciliary muscle forms a ring around

A

the posterior chamber

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22
Q

Describe the appearance of endothelial cells of capillaries in the choroid, and why this appearance is important.

A

endothelial cells of capillaries in choroid are fenestrated and provide nutrients to RPE cells, which transport nutrients to rods and cones of retina

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23
Q

Ganglion cells have their cell bodies in the ganglion cell layer. Where are its dendrites and axons located?

A

dendrites = inner plexiform layer

axons = nerve fiber layer

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24
Q

From out to in, what are the components of the cornea?

A

stratified squamous epithelium

Bowman’s membrane (basement membrane)

stroma

Descemet’s membrane (endothelial basement membrane)

corneal endothelium

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25
Q

Describe the composition of the lens capsule.

A

capsule itself made of collagen and proteoglycans

its basal lamina is made of Type IV collagen

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26
Q

Which structure of the eye contains most of its vasculature?

A

uvea

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27
Q

What are the two primary functions of ciliary bodies?

A

control lens shape by changing tension on zonules via circularly oriented ciliary muscle

produce aqueous humor via inner epithelial cells on ciliary processes.

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28
Q

What is the function of the pigmentation in the outer epithelial cells of ciliary bodies?

A

blocks stray light

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29
Q

What is the relationship of the retina to the uvea/choroid?

A

RPE cells are attached to the choroid

rest of retina is plastered by hydrostatic pressure of vitreous body to RPE layer

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30
Q

What specific features demark the appearance of the limbus?

A

disappearance of Bowman’s membrane from cornea

appearance of vasculature from sclera

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31
Q

Describe the role of ciliary muscle in the eye’s focusing on objects. (5)

A

contractions constrict this ring → releases tension on zonules → lens adopts rounder shape → increases refraction → allows eye to better focus on close objects

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32
Q

Define myopia.

A

nearsightedness = impaired ability to focus on distant objects caused by cornea being too far away from retina

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33
Q

Describe the outer epithelial cell layer of ciliary bodies. (2)

A

pigmented

continuous w/ pigmented epithelial cells of iris and RPE

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34
Q

What is the function of the iris?

A

regulates amount of light that reaches retina

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35
Q

Where is the trabecular meshwork found in the eye?

A

junction of iris and limbus

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36
Q

What are horizontal cells?

A

interneurons that integrate signals from photoreceptor cells and influence signals between photoreceptor cells and bipolar cells

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37
Q

What is the most refractile part of the eye?

A

cornea

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38
Q

What structures are found in the inner plexiform layer?

A

dendrites of ganglion cells

axons/dendrites of bipolar cells

axons/dendrites of amacrine cells

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39
Q

Define and describe the optic disc.

A

site where optic nerve exits eye

no photoreceptors → “blind spot”

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40
Q

Neurologically speaking, why is the nerve fiber layer critical to eye function?

A

axons of ganglion cells in nerve fiber layer exit eye through opitc nerve and carry signals to thalamus → visual cortex o brain

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41
Q

What is the function of retinal pigmented epithelium (RPE) cells? (3)

A

maintain functionality of photoreceptor cells

melanin pigment prevents backscattering of light

phagocytose photoreceptor debris

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42
Q

What structure is responsible for the shape of the orbit?

A

sclera

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43
Q

(T/F) The iris has an anterior epithelium.

A

False. The iris only has a (highly pigmented) posterior epithelium.

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44
Q

What is a major structural difference between bipolar and horizontal cells?

A

bipolar cells extend into both inner and outer plexiform layers, but horizontal cells only extend into outer plexiform layer

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45
Q

Describe the epithelium of the conjunctiva.

A

continuous with skin and corneal epithelium

non-keratinized stratified w/ surface squamous, cuboidal, or low columnar

goblet cells in columnar areas

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46
Q

What structures are found in the myoepithelial layer of the iris? (2)

A

melanin

forms the dilator pupillae muscle

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47
Q

What is glaucoma?

A

loss of visual field, most commonly resulting from loss of ganglion cell neuron

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48
Q

What is the conjunctiva?

A

mucous membrane that lines inner surface of eyelids (palpebral conjunctiva) and eye surface (bulbar conjunctiva) of sclera

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49
Q

What is the macula lutea?

A

region of the retina with the highest density of cones (this region contains the fovea centralis)

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50
Q

What are canals of Schlemm?

A

open-ended circular vessels that carry aqueous humor from trabecular meshwork to venous system (via episcleral veins)

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51
Q

What is the function of the blood-aqueous barrier?

A

restricts movement of material from blood/interstitium to aqueous humor and vitreous body

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52
Q

What is the function of the corneal endothelium?

A

regulates and maintains stromal water content

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53
Q

When does onset of presbyopia occur?

A

40-50 years old

54
Q

Describe the properties of the cornea. (4)

A

located centrally

where light enters

most refractile part of eye

most important for focusing images on retina

55
Q

The uvea is composed of

A

iris

ciliary body

choroid

56
Q

The iris determines eye color. Describe how melanosomes in the iris influence eye color.

A

lots of melanosomes = brown eyes

few = blue eyes

intermediate = green eyes

57
Q

Define astigmatism.

A

aspherical cornea that leads to light rays not sharply focused onto retina

58
Q

What is the sclera?

A

opaque, dense irregular connective tissue that forms white of eyes

59
Q

Describe how the photoreceptor layer, containing rods and cones, is associated to the RPE layer. (2)

A

there is no physical linkage between the photoreceptor layer and the RPE layer

association is purely hydrostatic

60
Q

Where do the photoreceptor cells synapse?

A

synapse with bipolar cells and horizontal cells in outer plexiform layer

61
Q

Describe how ciliary bodies contribute to the blood-ocular barrier.

A

continuous capillaries in the ciliary body’s highly vascularized stroma have tight junctions that contribute to blood-ocular barrier

62
Q

What instrument is used to view the retina?

A

opthalmoscope

63
Q

Which structures contribute to the blood-ocular barrier? (2)

A

tight junctions in:

continuous capillaries of ciliary body stroma

inner epithelial cell layer of ciliary body

64
Q

What is aqueous humor?

A

plasma-derived fluid that has less protein but more pyruvate/lactate than plasma

65
Q

What is the function of the blood-retinal barrier?

A

restricts movement of materials from blood of retinal and choroidal capillaries to retina

66
Q

Define laser-assisted in-situ keratomileusis (LASIK).

A

similar to PRK except that corneal epithelium is cut and peeled back to form flap prior to laser reshaping of corneal stroma

67
Q

Define hyperopia.

A

farsightedness = impaired ability to focus on nearby objects caused by cornea being too close to retina

68
Q

The retina belongs to which nervous system?

A

the retina is part of the central nervous system

69
Q

What structures are found in the outer plexiform layer?

A

axons of photoreceptor cells

axons/dendrites of bipolar cells

axons/dendrites of horizontal cells

70
Q

What are the two components of the blood-ocular barrier?

A

blood-retinal barrier

blood-aqueous barrier

71
Q

What is the trabecular meshwork?

A

series of baffles that conveys aqueous humor from the anterior chamber to the canal of Schlemm

72
Q

Define radial keratotomy (RK).

A

incisions near center of cornea to correct mild myopia

73
Q

What are amacrine cells?

A

interneurons that regulate bipolar neuron transmission from photoreceptor cells to ganglion cells

74
Q

(T/F) The sclera is contiguous with the corneal stroma.

A

True.

75
Q

What are zonules?

A

elastic ligaments that connect basal lamina of inner epithelial cells of ciliary processes to the capsule of the lens

76
Q

Differentiate between retinal and retinol use in the eye.

A

retinal = used by rhodopsin

retinol = used by iodopsin

77
Q

What is the function of the lens?

A

aids focusing of nearby objects onto retina

78
Q

What is the composition of the dilator pupillae?

A

myoepithelial cells

79
Q

What is the outer limiting membrane?

A

membrane that separates outer nuclear layer (photoreceptor nuclei) from photoreceptor layer (rods and cones)

80
Q

What are the three specialized regions of the retina?

A

macula lutea = area with cones

fovea centralis = center of macula

optic disc = site where optic nerve exits on orb

81
Q

Where in ciliary bodies is melanin found?

A

outer epithelial cells

82
Q

How are RPE cells connected to each other?

A

tight junctions

83
Q

Which retinal layers contribute to the blood-retinal barrier?

A

RPE

outer limiting membrane

nerve fiber layer

84
Q

Which structure of the eye is most important for focusing images on the retina?

A

cornea

85
Q

The inner epithelial cells of ciliary bodies are connected by

A

tight junctions, which prevent leakage of fluid/macromolecules from posterior chamber into ciliary processes

86
Q

Describe the properties of Descemet’s membrane. (2)

A

thick basal lamina of corneal endothelium

densely packed collagen fibrils to block diffusion of macromolecules b/w stroma and anterior chamber

87
Q

What forms the blood-aqueous barrier?

A

inner epithelial cells of ciliary processes

endothelial cells of capillaries in contact w/ aqueous humor, mostly in iris

pigmend epithelial cells of uvea

Muller cells in inner limiting membrane

88
Q

Define astigmatic keratotomy (AK).

A

incisions on steepest part of cornea to correct astigmatism

89
Q

Aqueous humor is pumped into

A

the posterior chamber

90
Q

What structures are found in the inner nuclear layer?

A

cell bodies of bipolar cells

cell bodies of horizontal cells

cell bodies of amacrine cells

cell bodies of Muller glial cells

91
Q

Describe the structure of ciliary bodies.

A

disk-shaped with large, hollow core

lumen lined with ciliary processes

2 layers (inner and outer) of epithelial cells

92
Q

What are the four primary components of the lens?

A

capsule

epithelium

lens fibers

zonules

93
Q

Describe the epithelium of the lens.

A

simple cuboidal (only one cell thick) epithelium on anterior surface

94
Q

Where are the nuclei of the photoreceptor cells located?

A

in outer nuclear layer (a layer of the retina)

95
Q

Describe the dilator pupillae.

A

arrayed radially

causes pupil to enlarge when it contracts

96
Q

What are the components of the iris?

A

pupil

posterior epithelium

myoepithelial layer

vascularized stroma

97
Q

What are rods and cones?

A

the photoreceptor cells in the retina

98
Q

Describe the inner epithelial cell layer of ciliary bodies. (2)

A

not pigmented

produces zonules (which are ligaments) anchored to its basal lamina that attach to the lends

99
Q

What is presbyopia?

A

loss of lens elasticity

100
Q

What is the inner limiting membrane?

A

innermost layer w/ basement membrane-like structure made by Muller cells that separates retina from vitreous body

101
Q

Describe the properties of the uvea.

A

middle layer

102
Q

What are cataracts?

A

loss of lens transparency

103
Q

Inflammation of the cornea originates from

A

the limbus

104
Q

What region of the retina has the highest acuity?

A

fovea

105
Q

What is found in the outer nuclear layer?

A

cell bodies and nuclei of photoreceptor cells (rods and cones)

106
Q

How are lens fibers connected to each other?

A

via gap junctions, which in essence forms a giant syncytium

107
Q

What structure gives RPE cells their color?

A

melanocytes

108
Q

What are the 10 layers of the retina, going from outside to in?

A

RPE cell layer

photoreceptor layer

outer limiting membrane

outer nuclear layer

outer plexiform layer

inner nuclear layer

inner plexiform layer

ganglion cell layer

nerve fiber layer

inner limiting membrane

109
Q

What maintains the stroma of the cornea?

A

keratocytes, a type of fibroblast

110
Q

List the properties of cones. (2)

A

color vision (RGB iodopsins)

most abundant in fovea

111
Q

What are the effects of presbyopia?

A

loss of lens elasticity → lens can’t deform and focus → hard to see objects up close

112
Q

Why do ciliary processes have to pump aqueous humor?

A

because hydrostatic pressure within ciliary processes is less than that in posterior/anterior chambers

113
Q

The cornea is rich in what structures and lacks what structures?

A

rich in free nerve fibers

lacks blood vessels or pigments

114
Q

What relays tension to the lens?

A

zonules

115
Q

What structure produces aqueous humor?

A

ciliary processes of ciliary bodies

116
Q

What causes glaucoma?

A

caused by excessive intraocular pressure (IOP) as result of excessive aqueous humor production or impaired aqueous humor outflow

117
Q

Describe the relationship between the conjunctiva and vasculature.

A

conjunctiva has abundant vasculature in areolar connective tissue under epithelium

118
Q

What is the sclera?

A

“whites of the eyes”

119
Q

What is the significance of the tight junctions between RPE cells?

A

control passage of material between choroid and rest of retina (i.e. forms part of blood-retinal barrier)

120
Q

What two muscles control the aperture of the pupil?

A

dilator pupillae muscle

constrictor pupillae muscle

121
Q

What creates the outer limiting membrane?

A

Muller glial cells

122
Q

Describe the properties of the corneal stroma. (3)

A

avascular, transparent connective tissue

alternating layers of keratocytes orthogonally arrayed with collagen fibrils

continuous with sclera

123
Q

What are the three layers of the wall of the eye?

A

corneosclera - outermost

uvea

retina - innermost

124
Q

Describe the characteristics of Bowman’s membrane. (4)

A

acellular

randomly arranged collagen fibrils

barrier to infection

does not regenerate if damaged

125
Q

What is the composition of the sclera?

A

mucosa (conjuctiva)

stroma of dense irregular connective tissue

126
Q

List the properties of rods. (4)

A

low-light vision

cannot discriminate colors

absent from fovea

use rhodopsin (GPCR)

127
Q

What is the composition of the constrictor pupillae?

A

smooth muscle cells

128
Q

What is the posterior epithelium of the iris?

A

layer of pigmented cells that blocks light and is rich in melanin

129
Q

What controls the shape of the lens?

A

ciliary body, via relative constriction of ciliary muscle

130
Q

Describe the highly vascularized stroma of the iris.

A

contains:

fibroblasts

macrophages

melanocytes

131
Q

Which retinal layer contains the majority of the retina’s microvasculature?

A

nerve fiber layer

Microanatomy (7 decks)

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