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Med Neuro Block 2 > Visual System 1: Anatomy > Flashcards

Visual System 1: Anatomy Flashcards

1
Q

peripapillary:

A

near or around the nerve head

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2
Q

papilledema:

A

swollen nerve head

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3
Q

Light passes through the transparent ________, _________, _________, and ________ before reaching the _________.

A
  • cornea, anterior chamber, lens, and vitreous
  • retina
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4
Q

Transparent tissues on the light path are surrounded by ___________________ (e.g., choroid & ciliary body) and a tough ________ to which extraocular muscles are attached

A
  • blood vessel-containing tissues
  • sclera
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5
Q

Structures of the Eye:

A
  1. Cornea
  2. Uvea
  3. Anterior Chamber
  4. Lens
  5. Vitreous Body
  6. Retina
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6
Q

Layers of the Cornea:

A
  1. Epithelium
  2. Bowman’s membrane
  3. Stroma
  4. Descemet’s membrane
  5. Endothelium
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7
Q

Function of the Cornea:

A
  1. Helps to shield the rest of the eye:
    • from germs, dust, and other harmful matter
    • Shares this protective task with the eyelids, the eye socket, tears, and the sclera, or white part of the eye
  2. Acts as the eye’s outermost lens:
    • Functions like a window that controls and focuses the entry of light into the eye
    • Contributes between 65-75 percent of the eye’s total focusing power
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8
Q

If the cornea contains no blood vessels, how does it get its nourishment?

A

receives its nourishment from the tears and aqueous humor that fills the chamber behind it

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9
Q

Why must the cornea remain transparent?

A
  • to refract light properly
  • the presence of even the tiniest blood vessels can interfere with this process
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10
Q

Epithelium:

A
  • Outermost region
  • 10 percent of the cornea’s thickness
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11
Q

Epithelium functions primarily to:

A
  1. Block the passage of foreign material into the eye and other layers of the cornea
    • such as dust, water, and bacteria
  2. Provide a smooth surface that absorbs oxygen and cell nutrients from tears
    • Then distributes these nutrients to the rest of the cornea.
  • Filled with thousands of tiny nerve endings that make the cornea extremely sensitive to pain when rubbed or scratched
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12
Q

Basement membrane:

A

serves as the foundation on which the epithelial cells anchor and organize themselves

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13
Q

Bowman’s Membrane:

A
  • directly below the basement membrane of the epithelium
  • composed of collagen
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14
Q

What happens if Bowman’s membrane is injured?

A
  • can form a scar as it heals
  • some vision loss may occur
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15
Q

Stroma:

A
  • Beneath Bowman’s layer
    • comprises about 90 percent of the cornea’s thickness
  • Primarily of water (78 percent) and collagen (16 percent)
    • does not contain any blood vessels.
  • Collagen gives the cornea its strength, elasticity, and form
  • The collagen’s unique shape, arrangement, and spacing are essential in producing the cornea’s light-conducting transparency
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16
Q

Descemet’s Membrane:

A
  • Under the stroma
  • Thin but strong sheet of tissue that serves as a protective barrier against infection and injuries
  • Composed of collagen fibers (different from those of the stroma) and is made by the endothelial cells that lie below it
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17
Q

What happens if Descemet’s membrane is injured?

A

Descemet’s membrane is regenerated readily after injury

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18
Q

Endothelium:

A
  • Extremely thin, innermost layer of the cornea.
  • Endothelial cells are essential in keeping the cornea clear
    • Normally, fluid leaks slowly from inside the eye into the stroma
  • Primary task is to pump this excess fluid out of the stroma
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19
Q

What would happen if endothelial cells did not have pumping action?

A
  • The stroma would swell with water, become hazy, and ultimately opaque
  • In a healthy eye, a perfect balance is maintained:
    • fluid moving into = fluid being pumped out
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20
Q

What happens if the endothelium is injured?

A
  • Once endothelium cells are destroyed by disease or trauma, they are lost forever
  • If too many endothelial cells are destroyed:
    • corneal edema and blindness ensue
    • corneal transplantation the only available therapy
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21
Q

_________ – affect the ________ and are the most common of all vision problems in this country.

A
  • Refractive errors
  • cornea
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22
Q

Myopia:

A

Nearsightedness:

  • When the cornea is curved too much, or if the eye is too long
  • faraway objects will appear blurry because they are focused in front of the retina
  • Myopia affects over 25 percent of all adult Americans
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23
Q

Hyperopia:

A

Farsightedness:

  • Opposite of myopia
  • Distant objects are clear, and close-up objects appear blurry
  • With hyperopia, images focus on a point beyond the retina
  • Hyperopia results from an eye that is too short
24
Q

Uvea (3 parts):

A
  1. Choroid
  2. Ciliary body
  3. Iris
25
Q

Choroid:

A
  • Largest component: 3 layers (out to in)
  1. vessel layer: medium sized arteries and veins, loose CT and melanocytes
  2. chorocapillary layer: capillaries arranged in one plane, fenestrated type
  3. Bruch’s membrane: 3 - 4 micron thick amorphous hyaline membrane that the retinal pigmented epithelia rests upon
26
Q

Ciliary body:

A

expansion of the stroma of choroid near the lens

  1. Contacts three regions: vitreous body, sclera, posterior chamber/lens
  2. Has projections called ciliary processes,
    • project toward lens
  3. Trabecular meshwork within ciliary body near limbus
    • Aqueous humor drained from anterior chamber via the trabecular meshwork
27
Q

Iris:

A

**covers lens; **regulates amount of light reaching the retina:

  1. anterior aspect made of vascular, loose CT with interspersed melanocytes
    • number of melanocytes in this layer determines eye color
  2. Posterior surface lined with a double layer of pigmented epithelium (absorbs light)
  3. 2 muscle masses rest upon the pigmented epithelium and regulate iris opening (pupil diameter)
28
Q

How is iris color determined?

A

Iris color is due to variable amounts of eumelanin (brown/black melanins) and pheomelanin (red/yellow melanins) produced by melanocytes. More of the former is in brown-eyed people and of the latter in blue- and green-eyed people

29
Q

Structure of the anterior segment of the iris:

A
  • Radially arranged myoepithelial cells form the dilator pupillae muscle between the vascular and pigment layer (sympathetic innervation)
  • Concentric smooth muscle bundles at the pupil margin (inner aspect of iris) form the sphincter pupillae muscle (parasympathetic innervation)
30
Q

Anterior Chamber:

A
  • Contains aqueous humor
  • Avascular
  • Involved in maintaining intraocular pressure
31
Q

Describe the pawthway for aqueous humor (starting from production):

A
  1. aqueous humor produced by the ciliary processes in the posterior chamber, passes from the posterior chamber ⇒ anterior chamber (between iris and lens)
  2. aqueous humor drained from anterior chamber via the trabecular meshwork
  3. from here, the humor passes into the canal of Schlemm that drains into the venous system
    • there is no direct connection between the canal and trabecula, the humor percolates through the tissue into the canal
32
Q

Glaucoma (types):

A
  1. primary open angle glaucoma (POAG)
  2. angle closure glaucoma
  3. normal tension glaucoma
  4. secondary glaucoma
33
Q

Open-angle or chronic glaucoma:

A
  • accounts for 80 to 85% of all cases
  • due to an obstruction in the drainage system of the eye
  • When the fluid reaches the angle, it passes too slowly through the meshwork drain
  • As the fluid builds up, the pressure inside the eye rises to a level that may damage the optic nerve and may result in vision loss
34
Q

Angle-closure glaucoma:

A
  • much more rare, but very severe, acute form of the disease
    • can cause blindness in 24-48 hours if not treated.
  • It results from poor access to the drainage system in the eye
  • referred to as angle-closure because the angle between the iris and the cornea narrows, blocking the drainage of the aqueous humor.
  • This sudden increase in pressure inside the eye causes intense pain and blurred vision
35
Q

Normal tension glaucoma:

A

optic nerve damage has occurred despite a normal IOP

36
Q

Secondary glaucoma:

A
  • another disease causes or contributes to increased eye pressure, resulting in optic nerve damage and vision loss
    • result of ganglion cell death
37
Q

Lens:

A

Very transparent structure:

  • avascular
  • little ECM
38
Q

Lens: Structural components

A
  • Capsule - ECM surrounding lens
  • Epithelium - anterior surface of lens
  • Lens fibers - body of the lens (no organelles)
39
Q

Lens: Functions/Specializations

A
  • Second to cornea in refractive power (~10 D)
  • lens is supported by system of fibers (suspensory ligament or zonules) attached to the ciliary body
40
Q

Accommodation

A
  • lens thinner when focused on distant objects, relaxed ciliary muscles
  • lens thicker when focusing on near objects, ciliary muscles contract, relaxing tension on zonule fibers thus thickening lens
    • anterior directed movement of ciliary body
41
Q

Vitreous Body:

A
  • Nearly acellular
  • major macromolecules: type 2 collagen & hyaluronic acid
  • Very transparent structure: 99% water & avascular
  • Nutritive function
42
Q

What are the two regions of the retina?

A
  1. Neural or sensory retina
  2. Retinal pigment epithelium (RPE)
43
Q

Neural (sensory) retina:

Regional specialization

A
  • Fovea (Latin for small pit):
    • region used for high acuity vision
  • Anteriorly the number of neural elements in the retina declines
    • becomes a single layer of epithelium (unpigmented) that covers the ciliary body
44
Q

Neural (sensory) retina:

Layers

A
  • Layer of photoreceptor (rod and cone) outer and inner segments; most posterior (external) so light passes through all other retina layers before it reaches photoreceptors
  • Outer nuclear layer (ONL): nuclei of rods and cones
  • Outer plexiform layer (OPL): location of synapses of rod and cone axons with next layer of neurons (bipolar)
  • Inner nuclear layer (INL): nuclei of bipolar neurons
    • also nuclei of horizontal and amacrine neurons and Müller glia
  • Inner plexiform layer (IPL): synapses of bipolar axons with ganglion cells
  • Ganglion cell layer (GCL): nuclei of ganglion cells
  • Nerve fiber layer (NFL): axons of ganglion cells that converge to form optic nerve
  • Inner limiting lamina: basement membrane of Müller glial cells
45
Q

General features of photoreceptors:

A
  • Inner segments – organelles for protein synthesis and energy production
  • Outer segments – flattened membrane discs with photosensitive visual pigments
    • Rods- long and slender
    • Cones - conical w/ membrane discs
46
Q
  • Rods and cones have __________ distributions across the retina.
  • Peak foveal cone density varies by at least a _________.
  • The human foveal cone mosaic is an efficiently packed mosaic, with the locations of cone centers forming a ____________.
A
  • unequal
  • factor of 3
  • triangular array
47
Q

Retinal Pigment Epithelium (RPE):

A
  • Simple, cuboidal, melanin‑containing epithelium between neural retina and Bruch’s membrane (BM)
  • ECM separating the RPE and the capillary bed of the choroid
  • Provides the outer blood‑retinal barrier
48
Q

Major functions of the RPE:

A
  • absorbs scattered light
  • transports nutrients and ions between photoreceptors & choriocapillaris
  • spatial buffering of ions in the subretinal space
  • reisomerization of all-trans retinal
  • outer segment renewal
  • secretion of growth factors for maintenance and structural integrity of retina
49
Q

Retinal Blood Supply:

The retina has a _________.

A

dual blood supply:

  • Outer retina: choriocapillaries
  • Inner retina: central retinal artery
    • central artery is a branch of the opthalmic artery
50
Q

Foveal Development:

A

Multiple anatomical events define foveal specialization:

  1. Cone packing increases
  2. Foveal pit develops after a thickening of the retina
  3. Site of incipient fovea is avascular all along
51
Q

Describe the recycling pattern of the RPE.

A
  • The RPE engulfs, digests, and recycles approximately 10% of the mass of each photoreceptor outer segment per day.
  • Outer segment phagocytosis occurs on a diurnal schedule:
    1. Peak of rod outer segment disc shedding occurring at dawn
    2. Peak of cone outer segment disc shedding occurring at dusk
52
Q

What is AMD? How is it treated?

A

Age-related Macular Degeneration

  • Leading cause of blindness in elderly in developed countries
  • Drusen develop within Bruch’s membrane
  • Vision loss is slow, and
    deteriorates central vision first (contrast to glaucoma).
  • Metamorphopsia is common (Amsler grid testing).
  • Risk factors: Family Hx AMD, smoking, blue eyes, CFH mutation
  • Treatment – focused on halting progression to “wet” – anti-VEGF
53
Q

Albinism:

A

Inherited disorder of melanin biosynthesis:

  • associated with absent or reduced melanin pigment in the eye
    • often the skin and hair. 1:17,000
54
Q

Oculocutaneous albinism (OCA):

A

Autosomal recessive:

  • OCA1A = no pigment anywhere
  • OCA1B = some pigment
  • due to “leaky” mutation allowing residual enzyme (tyrosinase)
55
Q

Ocular albinism (OA):

A

X-linked:

  • typically normal skin and hair
56
Q

Visual symptoms are _________.

A

universal:

  1. nystagmus
  2. refractive errors
  3. photophobia
  4. reduced acuity
  5. macular translucency
  6. iris transillumination
  7. altered retinostriate projections
  8. foveal hypoplasia
    • arrested foveal development

Med Neuro Block 2 (13 decks)

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