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Dispensing > Optics and Light > Flashcards

Optics and Light Flashcards

1
Q

What are the two theories of light?

A

Corpuscular and Electromagnetic

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2
Q

Explain the Corpuscular Theory of light

A

Light is bundles of radiant energy called PHOTONS. Photons move in straight lines.
This theory explains the formation of shadows

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3
Q

Explain the Electromagnetic Theory of light

A

Light travels in WAVES, but each point of light moves in s straight line = LIGHT RAYS
Waves travel in concentric circles at a constant speed of 186,000 miles/second
Explains how light splits into colours through a prism

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4
Q

What does UV 400 mean?

A

A lens that provides nearly 100% protections from wavelengths up to 400 nm

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5
Q

What is a nanometer?

A

A universal measurement for a wavelength

1 nm = 1 billionth of a meter ( 0.000 000 001 m)

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6
Q

What is the relationship between wavelengths and health?

A

The shorter the wavelength (UV) the more biologically harmful the radiation will be

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7
Q

Please list the wavelength ranges for visible light + ultraviolet light

A 
Red: 620-670
Orange: 590-620
Yellow: 560 -590 
Green: 490-560
Blue: 450-490
Purple: 380-450
UVA: 320-400
UVB: 290-320
UVC: 200-290
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8
Q

What are the different categories of UVA light known for?

A

UVA: Tanning and long term exposure damage (AMD)
UVB: Burning and Cataracts
UVC: Immediate short term damage (Welder’s flash)

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9
Q

What are 5 risk factors for UV exposure

A
  1. Equator Regions
  2. Time of Day (higher between 10 am and 3 pm, but there is more damage at dusk and dawn as the sun is more at eye level)
  3. Higher altitudes (thinner air and less protection)
  4. Sand (reflect 20-30%)
  5. Water and snow (reflect 85-95%)
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10
Q

Why is it important for children to have UV protection?

A

Children do not have any inherent UV protection in their eyes until 18-19

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11
Q

Define Emmetropia

A

“Normal” eye. When looking at an object in the distance and the eye is at rest, the image is infects.

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12
Q

What is the average length of an eyeball?

A

25 mm along the visual axis

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13
Q

Define Ammetropia

A

“Abnormal” eye. Refraction error

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14
Q

What are the three classes of ammetropia?

A
  1. Hyperopia
  2. Myopia
  3. Astigmatism
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15
Q

Define Hyperopia.

a) What are the two types?

b) How is it corrected?

A

Light is focused behind the retina when looking at a distant object and the eye is at rest.

a) 1. Axial: the eyeball is too short
2. Refraction: the cornea is too flat
b) With a plus lens

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16
Q

Define Myopia.

a) What are the two types?

b) How is it? corrected

A

Light is focused in front of the retina when looking at a distant object and the eye is at rest.

a) 1. Axial: the eyeball is too long
2. Refractive: the cornea is too steep
b) With a minus lens

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17
Q

Define pseudomyopia

A

A cramp or spasm in the ciliary muscle which causes the lens to never be fully relaxed. This causes accommodation to occur even when the eye is looking at an object in the distance

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18
Q

Define Astigmatism.

a) What is the most common cause?

A

A condition that occurs when parallel light rays do not form a single image.
a) When the cornea is not completely spherical

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19
Q

Define regular astigmatism. How is it corrected?

A

Astigmatism when the two sets of light rays at 90 degrees apart. It is corrected with glasses/contact lenses

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20
Q

What are the 5 types of regular astigmatism?

A
  1. Simple Myopic - one set of rays focuses on the retina and the other set focus IN FRONT of the retina
  2. Compound Myopic - Both sets of light rays focus IN FRONT of the retina, but at different points
  3. Simple Hyperopic - one set of rays focuses on the retina and the other set focus BEHIND the retina
  4. Compound Hyperopic - Both sets of light rays focus BEHIND the retina, but at different points
  5. Mixed - one set of light rays focuses in front of the retina and the other set focus behind the retina
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21
Q

Define Corneal Astigmatism

A

Astigmatism that occurs because the curvature of the cornea is not spherical

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22
Q

Define Lenticular Astigmatism

A

Astigmatism that occurs because a Lens of IOL is tilted

23
Q

Define Irregular Astigmatism. How is it corrected?

A

Astigmatism caused by disease or trauma. Corrected only by surgery or RGP lenses

24
Q

What are 5 characteristics of plus lenses?

A
  1. Thick middle and thin edges
  2. Converges light
  3. “Against” Motion
  4. Magnifies
  5. Power increases as it moves away from the eye (so compensate weaker)
25
Q

What are 5 characteristics of minus lenses?

A
  1. This middle and thick edges
  2. Diverges light
  3. “With” motion
  4. Minifies
  5. Power decreases at it moves away from the eye (so compensate stronger)
26
Q

Fill in the Blanks based on effective power

PLUS LENSES MINUS LENSES

IN _______ ________

OUT _______ ________

A

PLUS LENSES MINUS LENSES

IN Weaker Stronger

OUT Stronger Weaker

27
Q

What is the equation for the index of refraction?

A

n = speed of light in air (1.00)/ speed of light in medium

28
Q

Define Abbe Value

A

The amount of chromatic aberration for a give lens material. The higher the abbe value, the better the optics

29
Q

Define the index of refraction

A

A relative measurement of how much light bends when passing from one medium into another. For glasses, the higher the index, the more the light bends

30
Q

What is the index of refraction and Abbe value for Crown Glass?

A 
n = 1.523
Abbe = 58
31
Q

What is the index of refraction and Abbe value for CR-39 Plastic?

A 
n = 1.49
Abbe = 58
32
Q

What is the index of refraction and Abbe value for Polycarbonate?

A 
n = 1.586
Abbe = 31
33
Q

What is the index of refraction and Abbe value for Trivex?

A 
n = 1.532
Abbe = 43-46
34
Q

What is the index of refraction and Abbe value for Mid Index Plastic?

A 
n = 1.60
Abbe = 42
35
Q

What is the index of refraction and Abbe value for High index Plastic?

A 
n = 1.67
Abbe = 32
36
Q

What is the index of refraction and Abbe value for Ultra High Index Plastic?

A 
n = 1.74
Abbe = 33
37
Q

What line on the Snellen chart is required to drive?

A

Line 6 (20/30)

38
Q

What line is 20/20 on the Snellen chart?

A

Line 8 - D E F P O T E C

39
Q

Define Aberration

A

A degradation of an image resulting when a point source of light does NOT result in a point image when going through a lens system

40
Q

What are the 6 types of Aberration?

A
  1. Chromatic Aberration
  2. Spherical Aberration
  3. Coma
  4. Marginal Astigmatism
  5. Curvature of Field
  6. Distortion
41
Q

Define Chromatic Aberration

A

Ability of a lens material to disperse light into colours. Uneven bending of wavelengths resulting in separate focal points manifesting as blur

42
Q

Define Spherical Aberration

A

Blur due to light bending in the periphery sooner than in the centre. This creates multiple foci which prevents a sharp image.

43
Q

Define Coma

A

When an object is off axis, multiple focal points occur that result in a comet shaped image.

Blur due to light bending in the periphery sooner than in the centre when light is entering the lens obliquely.

44
Q

Define Marginal Astigmatism

A

When rays from an off axis POINT pass through the centre of a spherical lens and focus as two off axis points as though through a astigmatic lens

(Narrow beams of parallel light hit the CENTRE of a lens obliquely)

45
Q

Define Curvature of Field

A

A straight object sits uneven distances from a curved lens which results in a curved image.

46
Q

Define Distortion

A

Bulging/uneven bending of light rays based on uneven thickness of a lens at the edge and the centre.

47
Q

How do you address spherical aberration?

A

No need, as the iris blocks the rays coming from the periphery. This only becomes problematic at night and when the pupils are dilated.
If necessary, this can be handled with pinhole glasses

48
Q

When is Coma a concern?

A

Night driving, as it is normally controlled by pupil size.

49
Q

What is another name for Marginal Astigmatism?

A

Bundles of oblique astigmatism

50
Q

What are the two types of aberration that are of the most concern?

A
  1. Marginal Astigmatism

2. Curvature of Field

51
Q

What was developed to fix Marginal Astigmatism?

A

The corrective curve series

52
Q

How is curvature of field fixed?

A

Your eye corrects the curved image and the corrective curve series

53
Q

When is distortion a concern? How is it fixed?

A

With higher prescriptions. It is minimized by optimized curves, smaller frames and lenses and **atoric/aspheric designs

54
Q

What does distortion look like I a plus lens vs a minus lens?

A

Minus lenses cause a outward bulge (barrel distortion)

Plus lenses cause a inward curve (pincushion distortion)

Dispensing (8 decks)

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