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Chika- SF2 > Histology of the Eye-Heinbockel > Flashcards

Histology of the Eye-Heinbockel Flashcards

1
Q

Overall Eye

A

The eye is a photosensitive organ to analyze form and color on objects based on the light they are reflected from.

It can self-adjust, self-focus, can adjust for light intensity. It then converts light to electrical impulses that are sent to the brain.

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2
Q

How does light travel into and through the eye?

A

light comes in through cornea–>pupil–>retina which comprises of several layers of cells and the light will continue until it hits the outer segment of the photoreceptors (rods and cone)

it shouldn’t really hit the choroid or sclera

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3
Q

What are the structures located in the anterior of the eye?

A
  • cornea
  • ciliary body: secretes aqueous humor
  • iris
  • lens
  • limbus: where the eyelids/conjunctiva takes off
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4
Q

What are the structures located in the posterior of the eye?

A
  • sclera
  • choroid: layer under the sclera
  • retinal pigment epithelium
  • photoreceptors
  • fovea (highest visual acuity)
  • optic papilla (blindspot)
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5
Q

How do we distinguish the anterior chamber from the posterior chamber?

A

-iris separates the anterior and posterior chambers

anterior is in front the ciliary body (zonule)
the posterior is behind it

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6
Q

What comprises the external layer of the eye?

A

fibrous coat, supportive function, INELASTIC (very important in terms of glaucoma)

comprises of the

  • sclera: opaque white
  • cornea: is transparent where light can pass through
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7
Q

What comprises the middle layer of the eye?

A

vascular, highly pigments

comprises of the:

  • choroid: which has lots of melanocytes giving it its brown color, richly vascularized with BVs and it brings nutritive substances to the eye
  • cillary body: has ciliary muscles that is connected to lens fibers; assist in focusing the lens (making it flatter or more round)
  • iris: in the middle of the eye; pigmented with lots of melanocytes giving us our eye color
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8
Q

What comprises the internal layer of the eye?

A

retinal coat (back of the eye)

comprises of
neural retina: sensory retina that houses the rods and cones (photoreceptors)

non-neural retina: which is pigmented epithelium

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9
Q

What does the vitreous body behind the eye contain?

A
  • region behind the lens

- water (99%), collagen, hyaluronic acid molecules

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10
Q

What type of connective tissue does sclera and choroid contain?

A

sclera: thick layer of DICT
choroid: loose connective tissue

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11
Q

What is the difference in function of the sclera and choroid?

A

Sclera: mainly a supportive function; protects, maintain shape; reason for being inelastic

Choroid: supplies nutrition to the eye; is richly vascularized with blood vessels; has melanocytes and can absorb stray light

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12
Q

Describe the layers of the retina.

A

top single layer of retinal pigmented epithelial cells cuboidal in shape; they absorb the light and make sure there is no bouncing back of the light

photoreceptors that have cell bodies with inner and outer segment; rods and cones

photoreceptors are then connected to bipolar cells which are connected to the retinal ganglion cells

retinal ganglion cells send their long axons out of the eye to the lateral geniculate nucleus which basically forms the optic nerve

SUMMARY:

  • outer layers of rods and cones
  • intermediate layer of bipolar neurons
  • internal layer of ganglion cells
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13
Q

What is the function of the retinal pigment epithelium?

A
  • absorbs light pigment granules
  • prevents back reflection of light striking retina
  • forms part of the blood-retinal barrier: tight junctions
  • sustains metabolism/pigment turnover of photoreceptors
  • outer segment turnover: phagocytose shed discs

bruch’s membrane is btw the retinal pigment cells and the choroid

RPE has processes full of pigments and has all of the synthetic machinery it needs to make pigment

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14
Q

Where does light conversion into electrical signals (phototransduction) occur in the eye?

A

outer segment of the photoreceptors

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15
Q

What are the differences and similarities between the two photoreceptors: rods and cones?

A

they both have a cell body with a little process that synapses to the bipolar cell; they have membrane discs and cilium that connects the outer and inner segments of the photoreceptors ; have abundant mitochondria because you need a lot of ATP for the NaATPase

RODS:

  • responsible for detecting low light intensity (dark)
  • images in shades of gray

CONES for color:

  • color, detail
  • higher light intensity
  • 3 types: blue, green, red
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16
Q

What is the importance of the retina’s thin and transparent nature?

A
  • allows for minimal distortion so phototransduction is not interfered with
  • graded potentials instead of action portantions
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17
Q

What is the structural junction between the retinal pigmented epithelium and photoreceptors?

A

there is NO structural junction between RPE and photoreceptors

pathology: can pull the pigment epithelium from the photoreceptors which will interfere with vision; can be corrected with laser surgery

18
Q

What layer of the retina would the light hit first?

A

nerve fiber layer of the retina that will travel to the ganglion cells eventually to the photoreceptors

19
Q

How many layers of cell bodies does the retina have?

A

3

outer nuclear layer: photoreceptors

inner nuclear layer: bipolar, horizontal, and amacrine cells

retinal ganglion cell layer (BIGGEST CELLS)

with plexiform layers in between making the synaptic connections

20
Q

What is the fovea?

A

the spot (thin shallow depression) that allows for high acuity vision

  • is abundant with pure cone photoreceptors that are tightly packed (highest packing density)
  • can discern details of anything you are looking
  • central is surrounded by the macula lutea (yellow xanthophyll pigments that act as sunglasses); because there is a lot of light coming into the fovea that is potentially damaging to the photoreceptors and thus you have some pigments in the ML surrounding the fovea to prevent damage of the photoreceptors

light at the posterior region of the optical axis

21
Q

What allows the fovea to have the highest visual acuity?

A
  • pure cone photoreceptors (no rods)
  • highest packing density
  • thinnest retinal region
22
Q

Describe Age related macular degeneration.

A
  • macula surrounds the fovea
  • somehow there is some debris that accumulates btw the RPE and the choroid where the Bruch’s membrane is located

if there is material accumulating, this has an effect on the photoreceptors pushing them away from the fovea damaging them; the photoreceptors degenerate; instead of having high visual acuity you have a dark spot in the visual field

23
Q

What is the optic papilla?

A
  • the blind spot where the optic nerve leaves the eye
  • retina is all around the back of the eye but the retinal ganglion cells have axons that need to leave the eye somewhere

this occurs at the optic papilla (blindspot)

so there are no photoreceptors in the blindspot meaning you cannot see in this region

SUMMARY:

  • axons of ganglion cells exit the eyeball
  • no photoreceptors
24
Q

What is the function of the cornea?

A

most focusing of light occurs here

  • directs rays to converge on the retina
  • this is why it is TRANSPARENT and AVASCULAR
25
Q

Why is the cornea being avascular significant?

A

if the cornea messes so does your vision

-corneal transplant is the most frequent transplant being performed as pts don’t have to be related or of the same blood type

26
Q

Describe the structure of the conjunctiva.

A

stratified columnar epithelium with mucous secreting goblet cells

(limbus is where the conjunctiva takes over after the sclera)

27
Q

Describe the cornea.

A

stratified non-keratinized squamous epithelium

with nerve fibers going in there (cornea is sensitive to touch which is a reflection of the nerve fibers going into the epithelium)

Bowman’s membrane

Stroma or substantia propria: main tissue of the cornea that is dense REGULAR CT; has lots of fibroblasts and occasional lymphocytes

Descemet’s membrane: basement membrane made up of type VII collagen

corneal epithelium is very active in pumping bicarbonate ions thus fluids out of the substantia propria into the anterior chamber; need to make sure the cornea is DEHYDRATED for light to get through

28
Q

What are some dysfunctions of the cornea that could affect vision in terms of its structure?

A

sometimes the endothelial cells get damaged or the cornea does not have the right shape so that the light will actually bend to hit the retina

lasix surgery: laser eye surgery that correct near/far-sightedness

29
Q

What are the two main requirements for the cornea to have light pass through it?

A
  • transparent
  • dehydrated

stroma has dense regular CT in the cornea is organized further assisting in light passing through

30
Q

What is the function of the iris?

A
  • responsible for giving us the eye color (the distribution and concentration of melanin-containing cells in stroma is determining the eye color)
  • separates the anterior and posterior chambers
  • has lots of melanocytes for brown or few for blue eyes
31
Q

What is the opening that is created by the iris?

A

pupil which is NOT an anatomical structure; its a hole that is created by the iris and getting bigger or smaller due to iris contraction or relaxation

32
Q

What is the direction of flow of the aqueous humor that is secreted by processes the ciliary body?

A

aqueous humor is secreted into the posterior chamber and flows around the iris through the opening created (pupil) into the anterior chamber and filters through the trabecular meshwork draining (transcytosis ) into through the canal of Schelmm

33
Q

What is the role of pigmented epithelium in the iris?

A

it is a myoepithelium (has muscle in it) meaning it can act to change the shape of iris pulling it back during contraction
-consists of two types of muscles

34
Q

What are the two types of muscles in the iris and what is their function?

A

circular constrictor muscles: pupil constricts as circular muscles contract (parasympathetic)

radial dilator muscle: pupil dilates as radial muscles contracts (sympathetic)

35
Q

What is the function of the ciliary body (processes and muscles)?

A
  • when the ciliary muscle contracts it changes the shape of the lens helping us to focus to see near or far objects so ciliary muscle is involved in accommodation
  • process secrete aqueous humor
36
Q

Is there pigment in the iris?

A

YES on the back of the iris

-it is a continuation of the retinal pigmented epithelium

it gives us our eye color

37
Q

What do the lens and RBCs/keratinocytes have in common?

A

they lose their organelles

38
Q

Describe the structure of the lens.

A
  • has a capsule and a cuboidal epithelium in the front which goes to the equatorial region and become fibers (cortical lens cells fibers to nuclear lens cell fibers)
  • lens fibers: elongated, protein-filled, loose organelles
  • lens transparency: crystallin proteins
  • cataracts (opacity in lens due to protein filled fibers) is a clinical condition in which the lens are NOT transparent
39
Q

What is the function of the lens?

A
  • image focusing component; highly ELASTIC (in youth)
  • age-dependent loss of elasticity (at some point we would have to wear glasses) AKA presbyopia

-changing shape to bring into focus divergent or more parallel rays

40
Q

What is the function of the aqueous humor?

A

it provides nutrients to the cornea (remember which is avascular)

41
Q

What is glaucoma?

A

clogging in trabecular meshwork which in turn increases intraocular pressure (remember sclera is already INELASTIC); so the excess pressure presses on the optic nerve in the back of the eye impairing vision

Chika- SF2 (63 decks)

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