Chapter 5- Dispensing part II (1) Flashcards

1
Q

What are the factors we need to consider in choosing frames and lenses?

A

1- Distance Rx- high or low Rx

2- The patient’s current type of specs- don’t want to change it to something too drastic that will make them uncomfortable.

3- Occupation- Safety considerations - certain people may need impact or chemical resistance in their glasses

  • Visual considerations- may have anti- reflective coating which will help assist them when working at a computer screen.
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2
Q

What are the considerations for distance Rx (high prescription)?

A

1- Lens thickness

2- Lens weight

3- Magnification/ minification- this will either make the eyes look bigger or smaller through the lens

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3
Q

The smaller the uncut lens…

A

The thinner the lens will look when it’s cut into a frame.

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4
Q

What is an uncut lens?

A

The big lens that the manufacturers produce that will be cut down to produce the lens that goes in the frame.

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5
Q

When it comes to lenses and frames, what should you always aim for?

A

Aim for the smallest frame and minimum decentration of lenses in frame.

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6
Q

What is decentration?

A

The difference of the distance between the optical centre and pupil distance.

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7
Q

What is the optical centre?

A

The point lying on the lens where light passes through without undergoing any deviation.

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8
Q

What do you want the boxed centre distance to be equal to?

A

The patient’s PD

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9
Q

What is the boxed centre distance

A

The distance from the centre of one lens to the centre of the other lens.

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10
Q

In a myopic lens, where is the thickest part?

A

It is thickest at the edges

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11
Q

In a hypermetropic lens, where is the thickest part?

A

It is thickest in the middle

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12
Q

Why does an oval type shape work well for a myopic lens?

A

Because this will cut out the thick bits from the top and the bottom of the lens.

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13
Q

Why does an oval type shape for a hypermetrope not work as well?

A

Because it is cutting into the thick part of the lens which means you end up with quite thick lenses at the top and the bottom.

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14
Q

What does an oval shape frame look better on aesthetically?

A

A myopic lens

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15
Q

What is the formula for refractive index?

A

n = Velocity of light in air/ Velocity of light in material

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16
Q

What does it mean if the n value for the refractive index is high?

A

It means that the material slows light down a lot as it passes through a material, which means it bends light more.

So a higher n value/ refractive index means that the material is better at refracting light

17
Q

What can you do to lens curvature and thickness if you have a high refractive index?

A

It can be reduced

18
Q

What are the advantages of a high refractive index on lenses?

A

1- Thinner lens

2- Lighter lens

19
Q

What are the disadvantages of a high refractive index?

A

1- The high refractive index materials are more expensive than the standard ones

2- More reflections from lens surfaces so an antireflective coating is necessary

20
Q

What do aspheric lenses do?

A

1- Creates a thinner, flatter lens profile

2- Reduces spectacle magnification- reduces the size of images seen

3- Good for high powered Rx (prescription)

21
Q

What are power rings used for?

A

For patients with a high myopic (minus prescription).

22
Q

What does Px stand for?

A

Patient

23
Q

How do myopic lenses make the world look?

A

Makes the world look smaller to px, and px’s eyes look smaller to everyone else (minification)

24
Q

How do hypermetropic lenses make the world look?

A

It magnifies everything

25
Q

What type of spectacle lenses might be appropriate for the following presbyopic patients?

1- 78 year old avid reader with osteoarthritis in the neck and upper spine

2- 68 year old office worker who drives and likes fiddling with her ipad at home

3- A 60 year old libarian who is struggling to see the titles of books when putting them away on higher shelves

A

1- Single vision lens, readers and distance

2- Progressive addition lenses

3- A trifocal lens with the reading lens on top.