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OPH 114 Optics > THE EYE AS AN OPTICAL SYSTEM > Flashcards

THE EYE AS AN OPTICAL SYSTEM Flashcards

1
Q

****The Visual system is the part of the?

A

Central Nervous System

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2
Q

Visible Light

A

It builds a representation of the world around us

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3
Q

First, white light is reflected off an object (the images we see are made up of light reflected from the objects we are looking at).

A

just read

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4
Q

****First light passes through the

A

Tear Film on the surface of the eye

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5
Q

****Second then through the

A

Cornea

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6
Q

****Third to the

A

Anterior chamber

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7
Q

****fourth then the light passes through the

A

Iris

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8
Q

The anterior chamber is filled with a substance called

A

aqueous

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9
Q

Whats the iris?

A

The iris is the colored part of the eye that controls the amount of light entering the eye.

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10
Q

what changes the size of the iris

A

Pupil

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11
Q

what happens when theres a lot of light incoming

A

The pupil will be small

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12
Q

Low light situations

A

Pupil will be larger Dialated

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13
Q

****The fifth is the

A

pupil

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14
Q

*****The sixth Step

A

INVERTED

After going through the iris, the light passes through the lens. The light (image) becomes inverted.

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15
Q

****The light proceeds down the _______ through the_______ to the ________.

A
  1. Visual Axis
  2. Vitreous
  3. Retina
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16
Q

****The Visual Axis

A

Is the path of light that starts the object being viewed and ends at the FOVEA

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17
Q

Where is the Fovea

A

Center of the macula

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18
Q

Where is the Retina and what does it do and contains

A

The retina lines the back of the eye and contains photoreceptor cells which 
convert this light into 
electrical impulses.

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19
Q

Where are electrical impulses transmitted from? Where does it start and finish

A

optic nerve which emerges from the back of the eye and extends into the brain.

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20
Q

As the retinal fibers leave the optic nerves, half of them (from each eye) cross over to the opposite side at the

A

Optic Chiasm

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21
Q

The fibers fan out into the posterior portion of the brain called the______. It is in this area of the brain that conscious recognition of visual 
impulses takes place 
and an image is “seen”.

A

Visual Cortex

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22
Q

******The human eye has 5 optical media?

What are the 5 optical media

A

Tears, cornea, aqueous, lens, vitreous

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23
Q

The light is

A

refracted at the interfaces between each of these media. The goal is to have a focused image before it lands on the retina.
 


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24
Q

Fibers then form the ______ Which continue towards a cell station in the brain called the ______

A

Optic tracts Lateral geniculate body

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25
Q

The tear is composed of 3 layers

A
  1. Outermost lipid or fatty layer
  2. Central layer is most aqueous
  3. Mucous layer
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26
Q

The tear film serves several functions

A

***** Its forms a smooth refractive surface on the epithelium by abolishing minute surface epithelial irregularities

* It maintains a moist environment for the epithelium (cornea) and protects it’s delicate surface

* It provides the cornea with nutrients

*it inhibits growth of microorganisms by mechanical flushing and antimicrobial action

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27
Q

Cornea

A

The cornea is a clear, transparent, dome shaped structure with a shiny surface. It has a convex shape that acts as a powerful lens. Most of the refraction of they eye takes place through the tears and cornea, about 75%.

28
Q

The cornea has 5 distinct layers


A
  1. The epithelium
  2. Bowman’s layer
  3. The stroma
  4. Descemet’s membrane
  5. The endothelium
29
Q

The epithelium functions as a barrier and as an important refractive optical surface. It regenerates rapidly and heals without leaving a scar.

 Why is this so important to humans??

A

read

30
Q

Aqueous

A

The aqueous is a clear liquid that fills the anterior and posterior chambers of the eye. It is similar in composition to plasma. It is produced by the ciliary body. It enters the posterior chamber, passes through the pupil into the anterior chamber and leaves through the trabecular meshwork. It helps maintain the shape and pressure of the eye.

31
Q

Crystalline Lens

A

The lens of the eye is a transparent, biconvex structure situated between the iris and the vitreous. It is suspended behind the iris by zonules. The lens is surrounded by a capsule, which is a transparent, highly elastic envelope. It consists of about 65% water, about 35% protein, and a trace amount of minerals. It refracts light by changing it’s shape.

32
Q

Refraction

A

of light occurs at each of these interfaces, and the total of these refractions helps to establish the refractive status of the eye (how well the eye can focus images onto the retina).

33
Q

Refraction occurs

A

because the optical structures of the eye each have different IRs as well as different curvatures.

34
Q

which one goes up or down

air to tears????

A

Light going from air to tears 
lower n –> higher n 
Light going from tears to cornea 
lower n –> higher n
Light going from cornea to aqueous
higher n –> lower n
Light going from aqueous to lens
lower n –> higher n
Light going from lens to vitreous 
higher n –> lower n

35
Q

The refracting power of a curved surface can be calculated by the following formula

A

P = (n2-n1) r(m)

36
Q

Refractive surgeries (PRK, LASIK, LASEK, SMILE) aim to change the refractive state of

A

the eye by increasing or decreasing the radius of curvature of the anterior cornea.



37
Q

Increase the r = decrease the refractive power of the eye

A

Reduce the r = increase the refractive power of the eye

38
Q

The 2 main factors that determine the power of a lens and thus its ability to refract light:

A

The index of refraction (density of the medium)

The curvature (radius of curvature)

39
Q

The distance from the center of a lens to the focal point is the

A

focal length

40
Q

The power of a lens is measured in

A

Diopters (D)

41
Q

The power is related to the focal length.


A

A 1 D lens will bend parallel light rays to a focal point that is 1 meter from the lens.


42
Q

D means F means

A

D = the dioptric power of the lens
F = focal length of the lens in meters

43
Q

whats the formula

A

D = 1/F or F = 1/D


44
Q

D = 1/F
So if the focal length is 2 m
½ = 0.50 D


A

F = 1/D So if the power is 4.00 D ¼ = 0.25 m

45
Q

If other units of measurement are used…

A

D = 1/F meters D = 100/F centimeters D = 1000/F millimeters D = 40/F inches

46
Q

A lens has a focal length of 4 inches. What is the power of this lens?

A

D = 40/F D = 40/4 D = 10 Diopters

47
Q

A lens has a focal length of 12 mm. What is the power of this lens?

A

D = 1000/F D = 1000/12 D = 83.33 Diopters

48
Q

A lens has a power of 15 D. What is the focal length in cm of this lens?

A

15 = 100/F 15(F) = 100 F = 100/15 F = 6.67 cm

49
Q

light rays are moving away from each other. Light rays emanating from a source of light are divergent.


A

Divergent

50
Q

Light rays moving toward each other are convergent. Convergent light rays usually do not occur in nature but are the result of the action of an optical system (eg, a lens).



A

Convergence is expressed in plus power. Therefore, a lens that causes convergence is expressed in (plus) red.. power (+).

51
Q

The power of a lens is typically rounded to 2 decimal places. Usually in 0.25 increments but sometimes you will see them in 0.12 D increments.
1.25


A

The sign (whether plus or minus) must always be noted if there is a power.
+/-

 +1.25 -1.25

52
Q

Do we need plus or minus power to converge light rays?

A

Therefore, the overall power of the eye must be plus.

53
Q

Here, the vergence and power changes provided by the 5 curved surfaces of the eye are summarized

A

picture slide 59

54
Q

Why do patient’s with dry eyes complain of blurry vision?

A

The greatest plus power in the eye is provided by the tear-cornea curved surface. When the surface is disrupted, a substantial amount of plus power is lost, resulting in a blur.




55
Q

****How does the process of vision occur?

A
  1. WHITE LIGHT reflected off an object
  2. Light Passes through TEAR FILM
  3. Then CORNEA
  4. ANTERIOR CHAMBER
  5. Anterior chamber has AQUEOUS
  6. IRIS
  7. PUPIL
  8. LENS
    9.
56
Q

*****Which part of the eye has the greatest refracting power?

A

Most of the refraction of they eye takes place through the tears and cornea, about 75%.

57
Q

****Radius Curvature?

A

The other variable we need to look at is radius of curvature (r) in meters (though commonly written in mm).

Spheres with a shorter radius (a smaller sphere) have base curves that are higher (or steeper) than spheres with a longer radius (a larger sphere) which are flatter.

58
Q

****Factors that determined the power of a lens

A

The refracting power of a curved surface can be calculated by the following formula…

P = (n2-n1)

r(m)

The 2 main factors that determine the power of a lens and thus its ability to refract light:

  • The index of refraction (density of the medium)
  • The curvature (radius of curvature)
59
Q

****Light going through center of lens is not refracted?

A

In any lens, the ray of light going through the center of the lens is not refracted. But all rays on either side will be refracted. They will either converge (come together) to form a point or diverge from a point (more on this later). This is known as the focal point.

60
Q

****Focal point

A

.

They will either converge (come together) to form a point or diverge from a point (more on this later). This is known as the focal point.

61
Q

****Focal point

A

.

They will either converge (come together) to form a point or diverge from a point (more on this later). This is known as the focal point.

62
Q

*****Focal length?

A

The distance from the center of a lens to the focal point is the focal length

63
Q

****Calculating the focal length or dioptric power of a lens?

A

The power of a lens is measured in diopters (D).

The power is related to the focal length.

A 1 D lens will bend parallel light rays to a focal point that is 1 meter from the lens.

D = 1/F or F = 1/D

D = the dioptric power of the lens
F = focal length of the lens in meters
64
Q

****Focal length in relation to lens power?

A

Lenses with shorter focal lengths have higher powers

longer focal lengths have lower powers

65
Q

***Convergence

A

Light rays moving toward each other are convergent. Convergent light rays usually do not occur in nature but are the result of the action of an optical system (eg, a lens).

Convergence is expressed in plus power. Therefore, a lens that causes convergence is expressed in plus power (+).

The power (or vergence power) of a lens describes its ability to converge or diverge light rays.

66
Q

****Divergence

A

Divergent light rays are moving away from each other. Light rays emanating from a source of light are divergent.

Divergence is expressed in minus power. Therefore, a lens that causes divergence is expressed in minus power (-).

67
Q

****The power of the eye?

How much power does the eye have?

A

, the overall power of the eye must be plus.

+62

OPH 114 Optics (11 decks)

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