Chapter 9 - Contact lenses I (1)

Question 1

What are the different types of contact lenses?

Answer 1

1- Rigid corneal lenses (RCL)

2- Soft contact lenses

3- Speciality lenses- either made up of rigid or soft contact lenses

Question 2

What are the properties of rigid corneal lenses?

Answer 2

1- Approx 9mm in diameter

2- Reusable (1-3 years)

3- Clean after each wear

Question 3

What are the properties of soft contact lenses (SCL)?

Answer 3

1- Approx 14 mm in diameter

2- Disposable or reusable- can last a day or can be used for 2 weeks, 6-12 months, etc

Question 4

What are the properties of specialty lenses?

Answer 4

1- You can have hybrid lenses- can be a combination of RCL and SCL

2- You can have ortho-keratology lenses- ortho keratology clinical procedure used in contact lenses to try and correct someone’s prescription.

Question 5

How do ortho-keratology lenses work?

Answer 5

This involves putting a lens in and wearing it overnight.

By wearing that lens overnight, the front of the eye reshapes in order to fit that lens.

So when they then take the lens out, the shape of the cornea changes and by it changing, it provides a prescription correction.

Question 6

What is the disadvantage of the way ortho-keratology lenses work?

Answer 6

These lenses don’t change the shape permanently and will go back to its normal shape over the next 48 hours.

So the patient has to wear these lenses every night in order for this to be effective.

Question 7

Rigid gas permeable lenses (RGP) is the same as…

Answer 7

Rigid corneal lenses (RCL)

Question 8

What is modalities?

Answer 8

Modalities means how often a contact lens is replaced.

Question 9

This is how often soft contact lenses can be replaced:

Answer 9

1- Daily disposables
2- 2 weekly
3- Monthly disposables
4- Annually

Question 10

How often can RCL be replaced?

Answer 10

1- Replacement every 1-3 years

Question 11

What is wear modality?

Answer 11

How the person wears the lens.

Question 12

For soft contact lenses, you can have three types of wear modality:

Answer 12

1- Daily wear modality- wear them during the day but not at night

2- Extended wear lenses- can be worn for up to 7 days and 6 nights

3- Continuous wear lenses- can be worn for up to 30 days and 29 nights.

Question 13

For RCL, the wear modality is…

Answer 13

Typically worn as daily wear modality

Question 14

What are the types of contact lens prescriptions?

Answer 14

1- Spherical
2- Toric
3- Multifocal

Question 15

The materials in soft lenses can be split into two types:

Answer 15

1- Hydrogel (Hy)- a soft polymer which contains water and transports oxygen

• Very comfortable

2- Silicone hydrogel- where the polymer material has silicone associated with it

• Allows for more oxygen than Hy
• Allows for people to sleep in lenses
• More expensive

Question 16

The materials in rigid lenses can be split into two types:

Answer 16

1- PMMA (polymethyl methacrylate)- No oxygen permeability which is not healthy for the eye

• Provides excellent vision

2- Gas permeable- much better oxygen permeability and much healthier.

Question 17

What are the baseline measurements that you have to measure for a contact lens fitting?

Answer 17

1- Spectacle prescription

2- Measure curvature of the cornea

3- Measure diameter of cornea

Question 18

What is the air gap?

Answer 18

The gap between the glasses and the eye.

Question 19

When we get rid of the air gap, the power of the lens…

Answer 19

doesn’t have to be the same to focus the light into the right place on the back of the eye.

Question 20

If there is a lack of air gap, what do you have to change in order to get that same focusing effect?

Answer 20

We must change the number of the lens that’s on the eye

Question 21

What is this?

Answer 21

A table which is used to convert spectacle Rx into an ocular Rx which is needed for contacts.

If the spectacle Rx is below +4.00DS, then you keep it the same. So +3.00DS will have the ocular Rx of +3.00DS.

If the corresponding value is like -6.12, round it to the nearest 0.25 which will be -6.00

Question 22

What is astigmatism?

Answer 22

Astigmatism is the imperfection in the curvature of the ocular cornea and/ or the crystalline lens.

Question 23

How would you correct astigmatism?

Answer 23

You use two different prescriptions in two different meridians.

Question 24

What is regular astigmatism?

Answer 24

Where the two meridians are 90 degrees apart

E.g, One meridian is 10 degrees which means the other meridian will be 100 degrees.

Question 25

What is irregular astigmatism?

Answer 25

Where the meridians are not 90 degrees apart. This could be due to eye disease, trauma, etc.