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Vision > The Eye > Flashcards

The Eye Flashcards

0
Q

What does the oblique muscle do?

A

The oblique muscles rotate the eye

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1
Q

What is the rectus muscle?

A

There are four rectus muscles which control the direction of the eye
They are the superior and inferior muscles which move the eye up and down
The lateral and medial muscles move the eye side to side

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2
Q

What is the sclera?

A

The sclera is the outer wall of the eyeball - the white of the eye

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3
Q

What is the vitreous humour?

A

Vitreous humour is the gelatinous fluid that fills the space between the lens and the retina

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4
Q

What are zonular fibres?

A

Zonular fibres support the lens and connect it to the ciliary muscles

The zonular fibres are also called suspensory ligaments

When they are taut the lens is flat and less powerful and can focus on objects far away from the lens

When they relax the lens is elastic and more spherical making it more powerful and able to focus on nearby objects

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5
Q

What is aqueous humour?

A

Water like fluid that fills the space between the cornea and the lens
If the amount of aqueous humour is too high then the internal pressure of the eye increases causing glaucoma.

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6
Q

What is the fovea?

A

The fovea is a region of the retina where the photoreceptors are most dense

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7
Q

What does the lens do?

A

The lens focuses light onto the retina
The lens changes shape to alter its focal length (accommodation), this is achieved by the relaxation and the contraction of ciliary muscles which surround the lens

To focus on near objects the ciliary muscles contract causing a fat lens which is relaxed and more curved allowing a heat refraction of light

To focus on distant objects the ciliary muscles reflex and pull the lens into a thinner shape with a less curved surface…less light refracted

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8
Q

What is far sightedness?

A

When an image is focused behind the retina..I.e past the retina.
Distant objects can be seen clearly
Close by objects are out of focus

Also known as hyperopia
Can be corrected by placing a convex lens in front of the eye

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9
Q

What is near sightedness?

A

Occurs when an object comes into focus before the retina
Objects nearby can be seen clearly
Objects in the distance are out of focus

Also known as myopia.
Corrected by placing concave lenses in front of the eye

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10
Q

What is presbyopia?

A

An increase in far sightedness with age. Objects nearby can not be focused on and must be held further away

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11
Q

What are the causes of near and far sightedness?

A

1- the shape of the eyeball may be too long or too short from front to back

2- degree of curvature of the lens may be incorrect or alter over time

3- ciliary muscles may be unable to relax or contract properly

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12
Q

What is the pigmented layer of the eye?

A

The external photoreceptor layer

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13
Q

What are the horizontal cells?

A

Found in the plexiform layer
They connect the output terminals of photoreceptors to each other
They also modify the transmission of signals from photoreceptors to bipolar cells

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14
Q

What are bipolar cells?

A

Bipolar cells relay signals from photoreceptors to retinal ganglion cells
Each bipolar cells connects to a single photoreceptor in the fovea and many photoreceptors elsewhere therefore resulting in high visual acuity in the fovea but low on the peripheral retina

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15
Q

What are amacrine cells?

A

Found in the inner plexiform layer
They connect he output terminals of bipolar cells to each other and influence the transmission of signals by bipolar cells

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16
Q

Name the photoreceptors in the eye?

A

Rods and cones

Rods outnumber comes by 20:1

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17
Q

What are ganglion cells?

A

Information is passed from the bipolar cells to the retinal ganglion cells
The ganglion cells convert the electrical signal into an action potential and pass it onto the brain

There are two types of ganglion cell;
Midget ganglion cells (P cells - parvocellular system) and parasol ganglion cells (M cells - mango cellular system)

P cells have small receptive fields and are sensitive to colour - sustained response
M cells have larger receptive fields and are sensitive to the movement of light not colour - transient response

Ganglion cells first synapse in the lateral geniculate nucleus in the thalamus (LGN) and then on to the primary visual cortex/striate cortex.
The left LGN received intro from the right eye and vice versa
The LGN has 6 layers

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18
Q

What cells are found in the inner nuclear layer?

A

Bipolar cells

2 types - on bipolars and off bipolars

Off bipolars are inhibited when light fall on photoreceptors therefore preventing an action potential reaching the brain

On bipolars are excited by light falling on photoreceptors and cause the ganglion cell to send an action potential

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19
Q

What is the photopigment in rods

A

Rhodopsin

20
Q

Name the three types of cone

A 
L cones (red cones) respond to long wavelengths
M cones (green cones) respond to medium wavelengths
S cones (blue cones) respond to short wavelengths
21
Q

What does the superior colliculus control?

A

Eye movement

The superior colliculus has three sensory maps
Visual, somatic and auditory

The superior colliculus is two small bumps found on the midbrain

22
Q

What is the binocular field of vision?

A

The overlap of the visual fields of the left and right eye

23
Q

What are the three pathways in the visual cortex?

A

Magnocellular pathway receive info from M type ganglion cells and analyses an objects motion

Parvocellular pathway receive info from P type ganglion cells and analyses the shape of an object

Koniocellular pathway analyses an objects colour

24
Q

What is the refractive index?

A

The amount by which a medium slows the speed of light passing through it (nmedium)
Calculated by by dividing the speed of light (c) by the speed of light in the medium (vmedium)

Low refractive index = light able to move faster
High reflective index = light moves slower

25
Q

What happens to the path of Light when it travels through a parallel sided block?

A

At the first surface the light is refracted towards the normal at the second surface it is refracted away from the normal
The light leaves the block at the same angle as it entered

26
Q

What happens to the path of light when it enters a triangular prism?

A

When the sides are no parallel there is an overall change in the direction of light

27
Q

What happens when light travels through a prism?

A

There are converging and diverging prisms that converge light on one point or appear to have diverged from one point seemingly on the other side of the lens. See pg. 37

28
Q

What is focal length?

A

The distance between the centre of a lens and the focal point
He focal length is a positive number in a converging lens and negative in a diverging lens

29
Q

Define the power (P) of a lens?

A

The ability of a lens to converge or diverge light
Calculated by dividing 1/focal length (f)
f is measured in meters
The power is measured in dioptres (D) which is the same as m-1
+power = converging lens and short focal length
-power = diverging lens and long focal length

30
Q

Name the four surfaces that refract light in the eye?

A

Cornea, aqueous humour, lens, vitreous humour

31
Q

How is the refractive power of a lens calculated?

A

P = (n2-n1)/r

n2 and n1 are the refractive indices of the medium the light is passing through
r is the radius of the curvature of the surface in meters

32
Q

What is the iris?

A

The coloured part of the eye
The iris is a muscular diaphragm which controls the size of the pupil
Coloured by melanin pigment

33
Q

What is the depth of field?

A

The amount of visual field that appears in focus - controlled by the constriction/diameter of the pupil

34
Q

What is the consensual light reflex?

A

When a light is shone in one eye and the pupil constricts, the other eye does the same automatically

35
Q

What is the near light reflex?

A

The decrease in pupil diameter when the eyes converge to look at a close object

36
Q

What is the cornea?

A

The clear part of the eyeball
It does not have blood vessels and therefore obtains it’s nutrients via diffusion from the aqueous humour behind the cornea
There are five layers of connective tissue in the cornea

37
Q

Name the five layers of the cornea?

A 
Epithelium
Bowmans layer
Stroma - mostly made of water and collagen - biggest section
Descemets membrane
Endothelium
38
Q

Name the two important requirements of the cornea for transparency?

A

It must not absorb light

It must not scatter light

39
Q

Name the three planes that the eye rotates around?

A

Vertical axis - eye moves side to side
Anterior-posterior axis - gives rise to rolling
Transverse horizontal axis-elevates or depresses the eye

40
Q

Define saccades?

A

This is the most common form of eye movement
It is the rapid and conjugate jumps made by the eye
Important for reason and examining stationary scenes

41
Q

What is saccadic omission?

A

The lack of awareness that our eyes are making saccadic movements
Achieved through visual masking which allows the perception of an image just encore and after an eye movement therefore masking the blurring of the rapid eye movement

42
Q

What are pursuit movements?

A

The movement of the eyes to peruse moving objects
Automatic reflex
Much slower and smoother than saccades which are rapid
Pursuit movements maintain a stationary image of a moving object on the fovea

43
Q

What is the vestibulo-ocular movement?

A

The reflex which enables he eye to fix on an object despite movement of the head

44
Q

What is diplopia?

A

Double vision caused by the disjunctive movement of the eyes and the failure of the eyes musculature

45
Q

What is an astigmatism?

A

A blurring of the vision as a result of light being refracted unevenly by the cornea. This can be due to an uneven surface on the cornea, variations in the curvature of the lens and changes in the lens due to diabetes.
Can be treated with laser eye surgery and glasses/contact lenses.

46
Q

What is a spherical aberration?

A

Where the spherical lens fails to focus all light rays to a single point

47
Q

What are chromatic aberrations?

A

The focal length of the lens-cornea system caries with the wavelength of the incoming light.
If the eye is focused on infinity, yellow is focused on the retina, blue light is in front of the retina and red light behind the retina.

48
Q

What is a cataract?

A

A cloudy lens.

Vision (5 decks)

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