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CNS Physio > Lecture 6 > Flashcards

Lecture 6 Flashcards

1
Q

What are the 2 major types of lenses?

A

1) Convex (converging) lens

2) Concave (diverging) lens

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2
Q

What do convex lens do?

A

They converge (collect) light rays in the focal point

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3
Q

In which type of lens are images seen upside down?

A

Convex lens

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4
Q

What do concave lens do?

A

Diverge (separate) light rays. (No true focal point)

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5
Q 
The direction of the focal point is different in each lens, that’s why we say that a convex lens is a \_\_(positive/negative) lens (the focal point is in front of it) , while the concave lens is
a \_\_(positive/negative) lens (the focal point is behind it) since it diverges the rays away.
A

Positive; negative

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6
Q

What does the focal length of the lens mean?

A

The distance between the center of the lens and the focal point.

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7
Q

What are 2 minor lenses?

A

1) Spherical Lenses: Converge light at a “Focal point”
2) Cylindrical Lenses:
Converge light in points on a “Focal line”

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8
Q

What is the Focusing Power of the lens?

A

A property of the lens that indicates how capable the lens is of changing the courses of light rays (bending them), in order for them to be focused at a certain point (positive power/
convergence) or separated away from a certain point (negative power/ divergence).

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9
Q

A shorter focal length indicates:

A

MORE power

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10
Q

What is the unit used to express the power of a lens?

A

Diopter (NOT Degree)

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11
Q

What is the formula for Diopter?

A

Diopter = (1)/(focal length in meters)

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12
Q

What does 1 diopter mean?

A

The ability to focus parallel light rays at a distance of 1 meter (a focal length of 1m)

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13
Q

What does 2 diopters mean?

A

The ability to focus parallel light rays at a distance of 0.5 meter (a focal length of 0.5m)

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14
Q

The increase in convexity =

A

Increases the ability of the lens to bend the light in a smaller angle

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15
Q

More convexity = __ focal length = __

A

Shorter; more power by the equation

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16
Q

Changing the convexity of the lens changes:

A

1) The power (positive relation)

2) The focal length (inverse relation)

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17
Q

To focus an image on the retina our eyes have 4 requirements:

A

1) Light refraction or bending of the light by the refractive media
2) Accommodation
3) Constriction (miosis) for near and dilation (Mydriasis) of the pupil for far.
4. Convergence and divergence of the eyes for binocular vision.

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18
Q

What are the 4 media that the light has to cross in order to get to the retina?

A

1) Cornea
2) Aqueous humor
3) Lens
4) Vitreous humor

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19
Q

Where is the retina?

A

17mm behind the refractive center of the eye (the focal length)

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20
Q

What is the total refractive power of the eye?

A

59 diopters (1000 mm/17mm)

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21
Q

Which media in the eye has the most refractive power?

A

The surface of the cornea (42 diopters out of almost 60)

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22
Q

What is accommodation?

A

An increase in the curvature of the lens for near vision.

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23
Q

What is the near point of vision?

A

The minimum distance from the eye an object can be clearly focused with maximum accommodation used

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24
Q

Where must all of the light rays be focused in our eyes?

A

On the fovea of the retina

25
Q

If an object is far away, then the angle between light rays is __. This means that:

A

Narrower; The amount of refraction required is less = a smaller convexity is needed (lower power)

26
Q

What is accommodation important for?

A

Focusing the image on the retina

27
Q

Under normal resting conditions, what is the accommodation of the eye?

A

The Lens is held in place by suspensory ligaments of the ciliary muscle which cause the lens to be almost flat.

28
Q

What is the accommodation of the eye when we want to increase the refractive power of the lens?

A

Contraction of the ciliary muscle attached to the ligaments pulls the ligaments forward and causes the lens to become fatter (more convex).

29
Q

What causes contraction of

the ciliary muscle AND the circular iris muscles?

A

The parasympathetic fibers of the oculomotor (CN3)

30
Q

What are the 2 muscles of the iris? What are they supplied by?

A

1) Circular muscle: Supplied by parasympathetic innervation
2) Radial muscle: Supplied by
sympathetic innervation

31
Q

Contraction of the circular muscle and relaxation of the radial muscle causes:

A

Miosis (Pupillary constriction)

32
Q

Contraction of the radial muscle and relaxation of the circular muscle causes:

A

Mydriasis (Pupillary dilation)

33
Q

Why does the pupil constrict more when looking at nearby objects?

A

Because near objects reflect a lot of light compared to distant objects.

34
Q

What happens if we look at objects between our eyes?

A

The light coming from the objects doesn’t exactly hit the retina in the right spot, so the axes of the eyeballs must change so the light hits the retina right.

35
Q

If we bring our finger close to our eyes, they rotate __. If we bring it farther, they rotate __.

A

Medially; laterally (back to midline)

36
Q

What is Presbyopia?

A

Presbyopia is the Inability to Accommodate (aging [40-50 years] associated far sightedness)

37
Q

What causes Presbyopia?

A

Progressive denaturation of the proteins of the lens making the lens
less elastic.

38
Q

What are the 2 errors of refraction?

A

1) Myopia (Near sightedness)

2) Hyperopia/Hypermetropia (Far sightedness)

39
Q

What is an emmetropic eye?

A

A normal eye, in which the image is always focused on the retina.

40
Q

If the distance between the lens and the retina is shorter than normal, what happens?

A

The image gets focused behind the retina by the resting eye, resulting in far sightedness.

41
Q

How can we fix far sightedness?

A

By increasing convexity of

the lens.

42
Q

How does accommodation work in far sighted people?

A

These people start accommodation on
distances that don’t require accommodation in normal
eyes, so by the time their eyes look at a distance let’s say of 40 cm, they would’ve reached the maximum level of accommodation possible, and can’t see objects that are closer than that.

43
Q

What is the near point?

A

The minimum distance people can see clearly at.

44
Q

What is the near point for far sighted eyes?

A

Near point is higher than normal people, so they can see farther objects, but
they cannot squish their lens more to see closer objects.

45
Q

How do we treat far sightedness?

A

Use convex lenses to converge the light.

46
Q

What is myopia (near sightedness)?

A

When the distance between the retina and the lens is more than normal, so the focus is formed in front of the retina.

47
Q

How do we treat near sightedness?

A

Use concave lenses to diverge the light. (To lessen convexity of the eye even further)

48
Q

What is astigmatism?

A

Unequal focusing of light rays due to an oblong shape of the
cornea.
When one of the planes isn’t in line with the others = creates another point of focus =blurriness and double
vision.

49
Q

How do we treat astigmatism?

A

By using cylindrical lenses that help focus the wrong plane correctly

50
Q

What are cataracts?

A

Cloudy or opaque area of the lens due to denaturation of the protein (coagulation) in the lens

51
Q

How do we treat cataracts?

A

By replacing the lens (original lens does not let light pass through)

52
Q

What is the Visual Acuity Test?

A

Used to test the ability of the eye to discriminate details (to
distinguish ‘two points’’).

53
Q

How is the Visual Acuity Test expressed?

A

By degrees of angles

54
Q

To sense two different points, they must:

A

Hit two different receptors

55
Q

What is the diameter of a foveal cone receptor?

A

1.5 micrometers

56
Q

The visual acuity test tests whether the angle formed by 2 light points is normal or not. What is considered a normal angle and distance?

A

1 minute at 10 meters (?)

57
Q

What does a visual acuity test of 6/6 mean?

A

The ability to see letters of a given size at 6 meters.

58
Q

What does a visual acuity test of 6/12 mean?

A

What a normal person can see at 12 meters, this person must be at 6 meters to see.

CNS Physio (8 decks)

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