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KNES259 > The Eye > Flashcards

The Eye Flashcards

1
Q

Three layers of the eye

A
  1. Schleroid
  2. Choroid
  3. Retina
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2
Q

Schleroid

A

-White of the eye
-Continuous with cornea

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3
Q

Choroid

A

-Blood vessel layer
-Iris and ciliary body

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4
Q

Retina

A

-Back and sides only
-contains photoreceptors

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5
Q

Vitreous humour

A

-Gelatinous
-Maintains shape of eye so that the lens focuses on retina

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6
Q

Aqueous humour

A

-Provides nutrients to the cornea (has no blood vessels)
-5 mL/day

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7
Q

Where does the aqueous humour drain?

A

-Canal of Schlemm and eventually enters the blood

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8
Q

Glaucoma

A

-Blocked drainage duct
-Aqueous humour builds up, building pressure that can damage the nerve

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9
Q

Pupil

A

Eye opening for light

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10
Q

Iris

A

-Colour of the eye
-Controls amount of light entering eye
-Circular muscles and radial muscles

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11
Q

Circular muscles of the iris

A

-Constrict (they relax) pupil in light conditions

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12
Q

Radial muscles of the iris

A

-Dilate pupil in dark conditions

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13
Q

Structures contributing to light refraction:

A

Cornea:
-Contributes the most because of liquid
-Curvature never changes so refractive ability remains constant

Lens:
-Refractive ability can be adjusted by changing curvature as needed for near or far vision

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14
Q

Refraction

A

Bending of light to focus on the retina

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15
Q

Accommodation

A

-Changing shape of lens to adjust to light coming into eye

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16
Q

Accommodation for far vision

A

-Light rays are coming in almost parallel because they have traveled so far
-They need less bending
-Ciliary muscles relax, pulling suspensory ligaments taut. The lens becomes flatter/weaker

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17
Q

Accommodation for near vision

A

-Light rays are coming in diverging (going away from each other)
-They need more bending
-Lens should be rounder
-Ciliary muscles contract, suspensory ligaments go slack. The lens becomes rounder/stronger

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18
Q

Convex lens

A

-Convergent
-Bends light rays inwards
-Lens of the eye

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19
Q

Concave lens

A

-Divergent
-Bends light rays out

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20
Q

Emmetropia

A

Normal vision

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21
Q

Myopia

A

-Near sightedness

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22
Q

What is wrong with the lens or eye in myopia?

A

-The lens is too strong (bending light too much) or the eye is too long (can’t reach the back of the eye)

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23
Q

Where is the focal point in myopia?

A

In front of the retina

24
Q

How do you correct myopia?

A

Concave lens diverge the light rays outwards

25
Q

Hypermetropia or hyperopia

A

Far-sightedness

26
Q

What is wrong with the lens or the eye in hyperopia?

A

Lens is too weak (not bending light enough) or eye is too short (going too far past retina)

27
Q

Where is the focal point in hyperopia?

A

Behind the retina

28
Q

How do you correct hyperopia?

A

Convex lens to bend the light more

29
Q

Presbyopia

A

-Loss of near vision with age due to stiffening of lens (harder to become round)
-Correct with reading glasses

30
Q

Where does visual transduction occur?

A

On the retina

31
Q

Layers of retina from deepest to superficial

A
  1. Outer layer of eye: Sclera and Pigmented choroid coat
  2. Retina: pigmented epithelium, receptor cells, horizontal cells, bipolar neurons, amacrine cells, ganglion cells
  3. Nerve fibres (to optic nerve)
  4. Light waves
  5. Vitreous humour
32
Q

Layers within retina

A
  1. Fibers of optic nerve
  2. Ganglion cells
  3. Amacrine cells
  4. Bipolar cells
  5. Horizontal cells
  6. Cones
  7. Rods
33
Q

What is the blind spot in our eye?

A

Where optic nerve leaves eye

34
Q

Name the eye structure that controls the amount of light entering the eye.

A

Iris

35
Q

Fovea

A

-Pinhead-sized depression in centre of retina
-No bipolar or ganglion cells on top
-Most distinct vision
-Has only cones (no filtering)

36
Q

Macula lutea

A

-Area immediately surrounding fovea
-High acuity
-Has only cones, but is overlaid with bipolars and ganglions

37
Q

Macular degeneration

A

-Loss of cones in macula and fovea
-Lose central vision
-Periphery ends up having better vision
-Leading cause of blindness in western hemisphere
-Wet - more blood vessels and bleeding
-Dry - atrophy of pigment

38
Q

What are the two photoreceptors in the eye? How are they different?

A

Rods:
-100 million per retina
-Vision in shades of grey
-High sensitivity (work well in low light)
-Low acuity
-Periphery
-Much convergence in retinal pathways

Cones:
-3 million per retina
-Colour vision
-Low sensitivity
-High acuity
-Concentrated in fovea
-Little convergence in retinal pathways

39
Q

What’s the wiring of rods to bipolars? How does this affect acuity and sensitivity?

A

100:1
-Low light needed to stimulate 1 bipolar because even though the light is low, its being fed to 100 rods (GPs) who will all give that information to the bipolar (summate). It is highly sensitive to light.
-Because there are 100 rods, the receptor field for the bipolar is quite large which means poor acuity

40
Q

What is the wiring of cones to bipolars? How does this affect acuity and sensitivity?

A

1:1
-Need a lot of light into one cone to stimulate the bipolar for an AP. It is not sensitive.
-Because there is only 1 cone, the receptor field for the bipolar is quite small which means better acuity. We know exactly which cell that signal is coming from.

41
Q

What is the rod pigment?

A

Rhodopsin

42
Q

What are the three types of cones?

A

Red Green and Blue

43
Q

In the dark, are the rods and cones polarized, hyperpolarized, or depolarized?

A

-Depolarized
-Na+ gates are open: they release the inhibitory NT glutamate
-Bipolar cells are inhibited (hyperpolarized)
-No APs to ganglions/optic nerve

44
Q

In the dark, is rhodopsin active or inactive?

A

Inactive

45
Q

What happens when light hits the retina?

A

-Photopigment absorbs light, activating it
-Activates transducin (g protein) and decreases cyclic GMP
-Closes Na+ gates: stops the release of glutamate
-Hyperpolarizes membrane (K+ leaves cell) to -70mV
-Closes calcium channels in synaptic terminal
-Decreases inhibition of bipolars: bipolars are excited and send GPs to ganglions, who decide to send APs to the optic nerve

46
Q

Why are rods good for night vision?

A

They only need a small amount of light to work

47
Q

What is colour blindness?

A

-Poor or lack of function in one or more colour cones

48
Q

Dark adaptation

A

-Reform more photopigment, which lowers the threshold to send an AP with more pigment
-Eyes become more sensitive
-More rods used
-Vitamin A needed for regeneration of rhodopsin

49
Q

Light adaptation

A

-Sudden break-down of photo-pigment from too much info coming in
-Results in bleaching
-Eyes become less sensitive with less photopigment (leave it broken down)

50
Q

Images on the medial side of the optic nerve…

A

-Cross over to the other side of the brain

51
Q

Why do we need to keep the bipolars inhibited?

A

-They get depolarized really easily (basically anytime they’re not being inhibited)

52
Q

List the structures that light passes through to get to the photoreceptor cells

A

Cornea, aqueous humour, pupil, vitreous humor, ganglion cells, bipolar cells, photoreceptor cells

53
Q

what lies between the lens and the retina?

A

vitreous chamber

54
Q

Circular muscles of the iris are controlled by the [dropdown 1] nervous system and cause the
pupil to [dropdown 2]. Radial muscles of the iris are controlled by the [dropdown 3] nervous
system and cause the pupil to [dropdown 4]. The circular muscles are controlled specifically by
the [dropdown 5] cranial nerve.

A

1: parasympathetic
2: constrict
3: sympathetic
4: dilate
5: oculomotor

55
Q

The first step in the visual transduction process that occurs in the retina is

A

the absorption of light by the photopigments

KNES259 (11 decks)

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