Chapter 5- Dispensing part II (1)

Question 1

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

Answer 1

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.

Question 2

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

Answer 2

1- Lens thickness

2- Lens weight

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

Question 3

The smaller the uncut lens…

Answer 3

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

Question 4

What is an uncut lens?

Answer 4

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

Question 5

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

Answer 5

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

Question 6

What is decentration?

Answer 6

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

Question 7

What is the optical centre?

Answer 7

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

Question 8

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

Answer 8

The patient’s PD

Question 9

What is the boxed centre distance

Answer 9

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

Question 10

In a myopic lens, where is the thickest part?

Answer 10

It is thickest at the edges

Question 11

In a hypermetropic lens, where is the thickest part?

Answer 11

It is thickest in the middle

Question 12

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

Answer 12

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

Question 13

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

Answer 13

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.

Question 14

What does an oval shape frame look better on aesthetically?

Answer 14

A myopic lens

Question 15

What is the formula for refractive index?

Answer 15

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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

It can be reduced

Question 18

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

Answer 18

1- Thinner lens

2- Lighter lens

Question 19

What are the disadvantages of a high refractive index?

Answer 19

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

Question 20

What do aspheric lenses do?

Answer 20

1- Creates a thinner, flatter lens profile

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

3- Good for high powered Rx (prescription)

Question 21

What are power rings used for?

Answer 21

For patients with a high myopic (minus prescription).

Question 22

What does Px stand for?

Answer 22

Patient

Question 23

How do myopic lenses make the world look?

Answer 23

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

Question 24

How do hypermetropic lenses make the world look?

Answer 24

It magnifies everything

Question 25

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

Answer 25

1- Single vision lens, readers and distance

2- Progressive addition lenses

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