posterior segment of the eye Flashcards

1
Q

the posterior segment of the eye comprises the back two-thirds of the eye, including:

A
  • the vitreous humor
  • the retina
  • the choroid
  • the optic disc
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2
Q

what is vitreous

A
  • transparent elastic hydrogel
  • occupies ~80% of volume of the eye
  • increased liquefaction with age
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3
Q

what is the vitreous composed of

A

water (99%), collagen, hyaluronic acid, hyalocytes

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4
Q

what are the functions of the vitreous

A
  • vascularization of the lens (during embryogenesis)
  • maintains ocular volume volume and shape
  • can be surgically removed (by vitrectomy)
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5
Q

layers of retina from outside in

A
  • nerve fiber layer
  • ganglion cell layer
  • inner plexiform layer
  • inner nuclear layer
  • outer plexiform layer
  • outer nuclear layer
  • photoreceptor layer
  • retinal pigment epithelium
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6
Q

optical coherence tomography

A

non-invasive imaging of the retinal layers

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7
Q

what are photoreceptors

A
  • cells that initiate vision
  • light activates opsin molecules that are stacked in discs in the outer segment
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8
Q

cones

A

vision in bright light, color detection, visual acuity

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9
Q

rods

A

vision in dim light

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10
Q

what is phototransduction

A
  • conversion of light into a change in the electrical potential across the photoreceptor cell membrane
  • it turns OFF the circulating dark current in photoreceptors
  • results in inhibition of glutamate release
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11
Q

what is the retinoid cycle

A
  • photon capture causes isomerization of 11-cis-retinal to all-trans-retinal
  • the retinoid (=visual) cycles regenerate 11 cis-retinal through a series of enzymatic reactions
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12
Q

what are areas of specialization in the retina

A
  • central areas of high RGC and cone density subserve higher visual acuity
  • fovea and macula
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13
Q

what is the choroid

A
  • posterior component of the uvea
  • layer of blood vessel and connective tissue
  • located between retina and sclera
  • provides nutrients and O2 to outer layers of the retina via the fenstrated capillary bed (choriocapillaris)
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14
Q

what is the tapetum lucidum

A

a biologic reflector system to enhance visual sensitivity in dim illumination

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15
Q

what is the optic disc

also called optic nerve head

A
  • myelination/shape varies across species
  • retinal arterioles and veins emerge from its surface
  • site where axons of RGCs exit the eye to form the optic nerve
  • the lamina cribrosa is a collagen structure that provides a structural support to RGC axons as they leave the eye
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