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ANP Exam - T > Lec 18: Vision > Flashcards

Lec 18: Vision Flashcards

1
Q

Accessory Structures of the Eye

A

Eyebrows, eyelids, conjuctiva

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2
Q

Eyebrows

A

overlie the supraorbital margins and:
- shade the eye
- protect the eyes from perspiration

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3
Q

Eyelids (palpebrae)

A
  • separated by the palpebral fissure
  • lacrimal caruncle (corner of eye) contains sebaceous &sweat glands
  • eyelash follicles richly innervated - trigger reflex blinking
  • tarsal glands lubricate eyelid and eye with an oily secretion
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4
Q

Conjuctiva

A

transpaerent mucous membrane that lines eyelids

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5
Q

Bulbar Conjunctiva

A

Cover the white of the eye which produces lubricating mucus to prevent drying of eyes

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6
Q

Lacrimal Apparatus

A
  1. The lacrimal gland produces and secretes tears (lacrimal secretion)
  2. Tears enter the conjunctival sac via excretory ducts of the lacrimal gland
  3. Tear flow down eyeball
  4. Then enter lacrimal canaliculi called lacrimal puncta
  5. drain into lacrimal sac
  6. tears empty via the nasolacrimal duct into the inferior meatus of nasal cavity
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7
Q

Eye muscle

Lateral Rectus

A

Moves eye laterally (VI abducens)

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8
Q

Medial Rectus

A

Moves eye medially (III oculotomotor)

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9
Q

Superior Rectus

A

Elevates eye and turns it medially (III oculotomotor)

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10
Q

Inferior Rectus

A

Depresses eye and turns it medially (III ocutomotor)

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11
Q

Inferior oblique

A

Elevates eye and turns it laterally (III ocutomotor)

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12
Q

Superior oblique

A

Depresses eye and turns it laterally (IV trochlear)

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13
Q

The eyeball is a fluid-filled sphere composed of three layers:

A

fibrous, vascular, and inner (retina)
- Lens divides the eye into anterior and posterior segments

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14
Q

Fibrous layer

A
  • dense CT that is avascular
  • Sclera (majority)
  • Cornea (anterior 1/6 of fibrous layer)
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15
Q

Sclera

A
  • protects and shapes eyeball; anchoring site for extrinsic eye muscles
  • continuous with dura mater where it is pierced by optic nerve
  • seen anteriorly as the “white of the eye”
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16
Q

Cornea

A
  • transparent layer (largely collagen & glycosaminoglycans); allows light entry and is important in light refraction
  • corneal endothelium: simple squamous; sodium pumps to maintain corneal clarity
  • lots of nerve endings; in a vulnerable location but capable of regeneration and repair; no blood vessels so no access to immune system (corneal transplants)
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17
Q

Vascular Layer (pigmented)

A

Choroid, ciliary body, iris

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18
Q

Choroid

A
  • immediately deep to sclera
  • vascularized; nourishes all eye layers
  • contains melanin to absorb light so as to minimize scatter
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19
Q

Ciliary Body

A

anterior 1/6
- structure surrounding the lens that connects the choroid and iris. It contains ciliary muscles, (smooth muscles) which control the shape of the lens
- B on diagram

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20
Q

Iris

A
  • eye colour; continuous with ciliary body posteriorly
  • central opening is the pupil
  • have 2 layers of smooth muscles to allow constriction (circular; PNS) versus dilation (radial; SNS)
  • Only a brown pigment, but varying amounts give different colour possibilities
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21
Q

Inner Layer (retina)

A

Innermost layer of the eyeball; it contains millions of photoreceptors (rods, cones) that convert light energy, other neurons involved in processing light responses, and gilia.

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22
Q

Inner Layer

2 layers

Which one is involved in vision

A

-Outer pigmented layer
-Inner neural layer

Only neural layer is involved

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23
Q

Inner Layer

Pigmented Layer

A

absorbs light, cells can be phagocytic, stores vitamin A

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24
Q

Inner Layer

Neural Layer

A

composed of photoreceptors (rods and cones), bipolar cells, ganglion cells

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25
Q

Inner Layer

Signals

A

Produced in response to light and spread from the photoreceptors to the bipolar cells and then to the innermost ganglion cells, where action potentials are generated.

26
Q

Inner Layer

Ganglion cells axons

A

Make a right-angle turn at the inner face of the retina, then leave the posterior aspect of the eye as the thick optic nerve.

27
Q

Inner Layer

Retina

A

Also contains other types of neurons-horizontal and amacrine cells-which play a role in visual processing

28
Q

Inner Layer

Optic Disc (blind spot)

A

Where the optic nerve exits the eye. It is a weak spot in the fundus (posterior wall) of the eye because it is not reinforced by the sclera

29
Q

Inner Layer

Why is optic disc called the blind spot?

A

It lacks photoreceptors, so light focused on it cannot be seen.

30
Q

Inner Layer

Why do we not notice the blind spots?

A

The brain uses a sophisticated process called filling in to deal with the absence of input.

31
Q

Inner Layer

The quarter-billion photoreceptors found in the neural layer are of 2 types:

A

-Rods
-Cones

32
Q

Inner Layer

Rods

A

dim light & peripheral vision, more numerous, don’t give sharp images;
specialized for light detection in low light environments

33
Q

Inner Layer

Cones

A

bright light, high resolution, colour vision;
specialized for resolving spatial differences and detecting color

34
Q

Inner Layer

Macula lutea (yellow spot)

A

An oval region that’s lateral to the blind spot of each eye and located precisely at the eye’s posterior pole with the fovea centralis in the its center; contains mostly cones

35
Q

Inner Layer

Fovea centralis

A

a small depression within the neurosensory retina where visual acuity is the highest. The fovea itself is the central portion of the macula, which is responsible for central vision; contains only cones

36
Q

Inner Layer

For us to visually comprehend a scene that’s rapidly changing

A

Our eyes must flick rapidly back and forth to provide the foveae with images of different parts of the visual field.

37
Q

Inner Layer

Aqueous Humour

A

supplies nutrients and oxygen to lens and cornea and carries
away metabolic wastes

38
Q

Inner layers

Vitreous Humour

A

*forms in the embryo and lasts our lifetime (unlike aqueous humor)
* found in the posterior segment
* transmits light, holds two retinal layers firmly together, intraocular pressure

39
Q

Internal Layer

The - and - focus light on retina

A

Cornea and lens

40
Q

Inner Layer

Cornea

A

anterior 1/6
- avascular
- transparent (smaller collagen fibers with low water content)
- stratified squamous epithelium
- inner surface is simple squamous
- allows light into eye
- focuses eye
- transplants easily because no antibodies

41
Q

Inner Layer

Pathway for light

A

cornea
↓
aqueous humor
↓
lens
↓
vitreous humor
↓
neural layer of retina
↓
photoreceptors

42
Q

Inner Layer

Light is refracted three times:

A
  1. cornea
  2. entry to lens
  3. leaving the len
43
Q

Inner Layer

normal (emmetropic eye) vision far point

A

is 6 m;
with distant vision, light from an object at far point approaches as nearly parallel rays, allowing it to be precisely focused on the retina – ciliary muscles are relaxed (SNS)and lens is fla

44
Q

Inner Layer

Close vision

A

light diverges as it approaches the
eye and so needs to be focused by the lens – ciliary muscles contract (PNS) and lens bulges

45
Q

Inner Layer

Three Events of Near Vision

A
  1. Accomodation of lens
  2. Constriction of pupils
  3. Convergence of eyeballs
46
Q

Inner Layer

Accomodation of lens

A

to allow image to be focused on the retina (near point of vision, with maximal lens bulging, is 10 cm from the eye (closer for children,
gradually farther as we age)

After age 50 eye can not accomodate = reading glasses

47
Q

Inner Layer

Constriction of pupils

A

PNS-mediated and involves contraction of sphincter pupillae muscles of iris to keep most divergent light rays from entering and causing
image to be blurry

48
Q

Inner Layer

Convergence of eyeballs

A

to keep object focused on retinal foveae – medial rectus muscle and oculomotor cranial nerve

49
Q

Inner Layer

Most refractive problems are related to eyeball shape

A
  1. Myopia
  2. Hyperopia
50
Q

Inner Layer

Myopia

A
  1. Myopia: nearsightedness; eyeball is long and distant objects focus in front of
    retina; but can focus close objects on the retina making close vision OK
51
Q

Inner Layer

Hyperopia

A
  1. Hyperopia: farsightedness; eyeball is too short and distant objects focus
    behind the retina; but their ciliary muscles contract almost all the time, moving
    the focus to the retina for distance; but unable to refract enough to bring close
    objects onto the retina
52
Q

Inner Layer

Concave lense

A

Concave lenses diverge
the light

53
Q

Inner Layer

Convex lens

A

Convex lenses converge
the light

54
Q

Photoreceptors

Receptive

A

embedded in pigmented layer

55
Q

Photoreceptors

Cilium

A

connects outer segment to inner segment

56
Q

Photoreceptors

Outer Segments

A

contain visual pigments (rhodopsins) that change shape as they absorb
light; visual pigments are embedded in disc
membranes

57
Q

Phototransduction

A
  1. Photoreceptors hyperpolarize (-70 mV) when exposed to light and this actually
    acts as a signal
  2. Photoreceptors remain depolarized (-40 mV) in the dark
58
Q

Light and Dark Adaptation

Coming from dark into bright light:

A
  • initially both rods and cones are stimulated (all we see is bright white light)
  • rhodopsin in rods bleaches as quickly as it is formed and transducin leaves the disc
    membranes, rendering the rods non-functional
  • cones gradually take over (5-10 minutes to max acuity)
59
Q

Light and Dark adaptation

Coming from light to dark

A
  • initially all looks dark because cones are no longer stimulated and the rods had been turned off
  • rhodopsin starts to accumulate in the rods and transducin moves back into the disc
    membranes
  • slower process – takes 20-30 min to have max vision in very dim light
60
Q

From the Retina to the Visual Cortex

Key Points regarding Visual (and
related) Pathways

A
  • axons of retinal ganglion cells form the
    optic nerve
  • most fibers of the optic tracts continue to
    the lateral geniculate body of the
    thalamus
  • other optic tract fibers end in superior
    colliculi (initiating visual reflexes) and
    pretectal nuclei (involved with pupillary
    reflexes)
  • optic radiations travel from the thalamus
    to the primary visual cortex
61
Q

Closer Look

A

1.Medial half of each retina receives
light rays from the lateral field of view.
2. Lateral half of each retina receives
light from the central part of the visual
field (and there is overlap here).
3. Medial fibers of the optic nerve
decussate at the optic chiasm
4. Each optic tract leaving the optic
chiasm contains fibers from the lateral
aspect of the eye on the same side
and the medial aspect of the opposite
eye
5. Each optic tract carries information for
the same half of the visual field

62
Q

Depth Perception

A
  • The visual field of each eye is
    about 170 degrees
  • There is considerable overlap in
    the middle area, but each eye
    sees on a slightly different angle
  • The primary visual cortex fuses
    the images from both eyes
    giving depth perception
  • Depth perception is lost if you
    are looking with only one eye

ANP Exam - T (11 decks)

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