Contact Lenses Types and Fitting Measurements

Question 1

What are the types of contact lenses

Answer 1

• Rigid Gas Permeable ( RGP )
• Soft Contact Lenses
• Speciality

Question 2

What are RGP lenses

Answer 2

• Made up of solid plastic
• Approx 9mm diameter
• Reusable ( 1 to 3 ) years
• Clean after each wear
• More comfortable

Question 3

What are soft contact lenses

Answer 3

• Approx 14mm diameter

- Disposable or reusable

Question 4

What are speciality contact lenses

Answer 4

• Re - usable

- For certain eye conditions

Question 5

What is meant by the term modality

Answer 5

How someone wears contact lenses

Question 6

Replacement for Soft lenses

Answer 6

• Daily disposable
• 2 - weekly
• Monthly disposables
• Annual

Question 7

Replacement for RGP

Answer 7

• Replacement every 1-3 years

Question 8

Wear modality for Soft lenses

Answer 8

• Daily (Daily Wear)
• 7 days and 6 nights ( Extended wear )
• 30 days and 29 nights ( Continuous wear - don’t take it out = not recommended )

Question 9

Wear modality for RGP lenses

Answer 9

• Daily (DW)

Overnight ( only with keratology)

Question 10

Are there dailys/monthlys for RGP lenses

Answer 10

No

Question 11

How do daily disposables work

Answer 11

Throw away at end of the day - no cleaning

Question 12

What are the type of prescriptions for CL’S

Answer 12

• Spherical
• Toric
• Multifocal

Question 13

What are spherical lenses for

Answer 13

Myopia/hypermetropia

Question 14

What are toric lenses for

Answer 14

Asitgmatism

Question 15

What are multifocal lenses for

Answer 15

Varifocal - presbyopia

Question 16

Which contact lens rx is most common

Answer 16

Spherical soft - vast majority

Then toric soft

Question 17

What are the different types of materials for CL’s

Answer 17

• Rigid lenses - PMMA and GP

- Soft lenses - Hydrogel and Silicone hydrogel

Question 18

What are PMMA lenses

Answer 18

• Rigid lens
• Very first
• No O2 permiability
• Excellent vision

Question 19

What are Gas Permeable lenses

Answer 19

• Much better O2 permeability - healthier

Question 20

What are hydrogel soft lenses

Answer 20

• Contains water - transports O2

- Very comfortable

Question 21

What are silicone hydrogel lenses

Answer 21

• Hydrogel with Silicone in it
• More oxygen than hydrogel
• More expensive
• Allow to use for extended wear/ continuous wear

Question 22

What are the baseline measurements for CL’s

Answer 22

• Spectacle rx - convert to ocular rx
• Measure curvature of cornea - keratometry
• Measure diameter of cornea - size of eye

Question 23

How to measure diameter of cornea

Answer 23

Horizontal Visible Iris Diameter….
Measure iris size - cornea diameter
Its hard to measure cornea cause its clear

Question 24

What is ocular rx

Answer 24

The rx for CL’s

Question 25

What is back vertex

Answer 25

How far away glasses sit from eye | If gap changes the power has to change as well

Question 26

What is the Back Vertex Distance

Answer 26

Its used to convert the rx using the vertex distance and back distance. Only for rx 4.00 and above

Question 27

What is astigmatism

Answer 27

2 focal points at back of eye, 1 on meridian and 1 on other meridian Imperfection in the curvature of ocular cornea and/or crystalline lens

Question 28

How do you correct astigmatism

Answer 28

Use two different rx's simultaneously in principle meridians

Question 29

What 2 places are astigmatism created

Answer 29

- Cornea - front surface (might be more curved one way and not so curved other way ) - In crystalline lens

Question 30

What are principle meridians

Answer 30

Powers - different directions

Question 31

What is regular meridians

Answer 31

Whatever one meridian is, other meridian is 90 degrees to it. E.g. 1st meridian - 10 degrees 2nd meridian - 100 degrees ( 10 + 90)

Question 32

What is irregular meridian

Answer 32

The difference between the 1st and 2nd meridians is NOT 90 degrees apart Due to trauma, disease e.t.c

Question 33

What value does meridian have to be between

Answer 33

0 and 180

Question 34

What does astigmatic spectacle rx cause

Answer 34

Blur - different powers in two principle meridians

Question 35

Symptoms of Astigmatism

Answer 35

- Blurry vision - Fatigue or eye strain - Distorted vision - Light sensitivity - Excessive squinting - Headaches

Question 36

What are the types of corneal astigmatism

Answer 36

- With the Rule | - Against the Rule

Question 37

What is With the Rule astigmatism

Answer 37

The vertical meridian is steeper ( more curved ) than the horizontal meridian. Flatter horizontal way

Question 38

What is Against the Rule astigmatism

Answer 38

- The horizontal meridian is steeper ( more curved ) than the vertical meridian Flatter vertical meridian

Question 39

What is the rules for choosing the rx

Answer 39

SPHERE: most positive CYL: difference between two powers AXIS: Orientation of the more positive power

Question 40

What does along mean for CL's

Answer 40

In that direction vertical

Question 41

What is meant by keratometry

Answer 41

The measurement of the principle radii of the anterior surface of the cornea ( tear film )

Question 42

How does karatometry work

Answer 42

``` The cornea ( tears ) acts as a mirror since light is reflected from it - measure radius of curvature of this ' mirror' Gives you principle meridian powers ```

Question 43

Why do keratometry

Answer 43

Determination of..... - Central Corneal Radius and and power in both principle meridians of cornea - Differentiate between regular and irregular astimgatism - Observe quality of tears and reflected mires - Measure NIBUT ( non - invasive break up time ) - Measurement of radius of contact lenses

Question 44

What do you always round the power nearest to

Answer 44

0.25D

Question 45

What is radius rounded closest to

Answer 45

0.05MM

Question 46

What does curvature correlate to

Answer 46

Certain corneal power

Question 47

Horizontal Visible Iris Diameter....

Answer 47

Why... for total diameter CL Measure with PD rule Expected 11.6mm ( between 10.2-13.0mm)