Properties of Contact Lens materials

Question 1

quality or state of the material that allows the oxygen to move through it

Answer 1

dk - Oxygen Permeability

Question 2

High oxygen content = ______

Answer 2

Higher the dk

Question 3

dk values:

Answer 3

Low dk = less than 30

Medium dk = 30- 60

High dk = higher than 60

Question 4

states how much oxygen goes through the lens

Answer 4

Dk/t - Oxygen transmissibility

Question 5

the Thinner the lens = the _____ amount of oxygen can pass through the lens

Answer 5

Higher

Question 6

Dk/t for daily wear:

Answer 6

25

Question 7

Dk/t for overnight wear:

Answer 7

87 and above

Question 8

• this is a measurement of the cornea’s oxygen thirst following lens wear
• allows practitioners to compare different performances of lenses

Answer 8

Equivalent Oxygen Performance - EOP

Question 9

describes oxygen flux through a contact lens as if the eye were responding to various amounts of atmospheric oxygen

generally conducted using lens materials of various thickness

Answer 9

Equivalent Oxygen Performance - EOP

Question 10

• most valid indicator of real-life clinical performance
• it is the measure of the percent increase in the corneal thickness with great precision

Answer 10

Corneal Swelling

Question 11

Four measurement used to evaluate tensile properties:

Answer 11

• Tensile Strength
• Modulus elasticity
• Coefficient of elongation
• Tear Strength

Question 12

• measure how much force can be applied to the material before it breaks
• the greater the force, the better the strength and the more durable the material

Answer 12

Tensile strength

Question 13

refers to the flexibility of the material

materials that has low ______ are more flexible

Answer 13

Modulus elasticity

Question 14

• refers to how far a lens material can be stretched before it will break
• value is stated by percentage based on the size of the lens sample tested

Answer 14

Coefficient of Elongation

Question 15

measurement refers to how much force has to be applied to a lens material before it will tear

Answer 15

Tear strength

Question 16

the higher the _____ lenses generally provide more oxygen to the cornea

Answer 16

Water Content

Question 17

High water content materials become _____ while on the eye

Answer 17

Dehydrated

Question 18

High water content tend to ______ than low water content lenses

Answer 18

lose more water

Question 19

a physical property of which defines how light rays are affected as they pass through the material

Answer 19

Refractive index

Question 20

as water content increases the refractive index _______

Answer 20

decreases

Question 21

Materials with low index of refraction will require ______ lens design to achieve the desired optical effect on power

Answer 21

Thicker lens design

Question 22

term which contact lens interact with the corneal tissue, therefore it is important to evaluate the physiological balance of the material with the ocular environment

Answer 22

Biocompatibility

Question 23

tests to evaluate biocompatibility:

Answer 23

• 21 day Rabbit test
• Resistance to microbial growth

Question 24

compatibility of the lens materials with lens care systems

Answer 24

Biocompatibility

Question 25

it is assessed in the laboratory periodically by measuring:

• water content
• sagittal value
• power thickness
• base curve

to make sure that the lens parameters are not changing

Answer 25

Dimensional Stability

Question 26

this ensures that the material can maintain consistent lens performance

Answer 26

Dimensional Stability

Question 27

since contact lenses are placed in the tear film, which is primarily made up of water,

this property must be always assessed prior to placement on the eye

Answer 27

Hydrolytic Stability

Question 28

term in which only materials that are stable in water can be used for contact lenses

Answer 28

Hydrolytic stability

Question 29

the more rigid the lens material is, the ______ they are to handle

Answer 29

easier

Question 30

is the characteristic of lens performance that is important to RGP materials.

Answer 30

Wettability

Question 31

With RGP lenses, wettability is tested in the laboratory by measuring the ______

Answer 31

wetting angle

Question 32

The higher the wetting angle, the _____ wettable the surface is

Answer 32

less wettable

Question 33

The wetting angle of a hydrophilic material is considered _____

Answer 33

ZERO