Unit 6: Contact Lenses

Question 1

Orthokeratology

Answer 1

Gas permeable lenses worn while sleeping to reshape the cornea

Question 2

Hard contact lens materials

Answer 2

-PMMA (Polymethylmethacrylate)
-GP (Gas permeable)

Question 3

Soft contact lens materials

Answer 3

-hydrogel
-Silicone hydrogel

Question 4

Characteristics of PMMA lenses

Answer 4

-worn by less than onepercent of contact lens wearers
-Very durable but not oxygen permeable
-Small diameter to allow cornea to breathe

Question 5

Characteristics of GP lenses

Answer 5

-Less than 10% of contact lens wearers
-Vision is better than with soft lenses
-Last longer
-Less comfortable than soft lenses
-Can’t be used for part time where

Question 6

Characteristics of HEMA lenses

Answer 6

-Worn by 90% of contact lens wearers
-Can be worn occasionally
-More comfortable and stable
-Less durable and more expensive
-Vision not as good
-Prone to deposits

Question 7

Characteristics of silicone hydrogel lenses

Answer 7

-All soft contact characteristics
-More expensive
-Easier to handle
-Reduced lens wettability

Question 8

Advantages of hybrid lenses

Answer 8

-Improved comfort over hard lenses
-Lower cost than scleral lenses
-Easier to remove than scleral
-More stable than soft toric lenses

Question 9

Disadvantages of hybrid lenses

Answer 9

-More expensive than soft or hard lenses
-More chair time to fit
-Limited ability to customize
-Insertion is similar to scleral

Question 10

Contact lens modalities

Answer 10

-Single use
-Two week
-Daily or extended wear
-Monthly
-Daily or extended wear
-Quarterly or yearly
-Daily wear only

Question 11

Types of ballast for toric lenses

Answer 11

-prism ballast
-Peri ballast
-Thin zone

Question 12

What is monovision

Answer 12

-Two different lenses, distance power in one by, near power in the other one
-Good for high astigmatism
-Compromises depth perception

Question 13

What are lenticular lenses

Answer 13

-Used for aphakic patients
-Sharply defined transition between carrier and prescription zone

Question 14

Eight contact lens fitting parameters

Answer 14

-Base curve
-Diameter
-Center thickness
-Edge design
-Oxygen transmissibility
-Water content
-Sagittal depth
-Wetting angle

Question 15

Base curve

Answer 15

-Curvature of the posterior surface
-the HIGHER the number, the FLATTER the lens

Question 16

Average diameter smallest to largest

Answer 16

-PMMA (7.5-8.8mm)
-GP (8.0-9.6mm)
-Soft (13.0-15.0mm)
-Hybrid (14.5mm)
-Scleral (15.0-25.0mm)

Question 17

How far away from the limbus should a soft contact lens be

Answer 17

2mm

Question 18

HVID

Answer 18

Horizontal visible iris diameter

Question 19

Center thickness

Answer 19

-Distance from the front surface of the lens to the back surface
-Hi plus we’ll have a thicker centre

Question 20

Dk

Answer 20

The oxygen permeability of the lens
D=The diffusion coefficient for oxygen movement in the material
k=The solubility constant

Question 21

Dk/t

Answer 21

The oxygen transmissibility of the lens
t=Centre thickness

Question 22

Three categories of water contacts and their percentages

Answer 22

High- 60%
Medium- 40-60%
Low- <40%

Question 23

What happens to lens characteristics as the water content increases

Answer 23

-More oxygen
-Lower stiffness
-Higher evaporation, decreasing comfort
-More fragile

Question 24

Sagittal depth

Answer 24

The distance from the centre of the lens to surface it’s sitting on

Question 25

Wetting angle

Answer 25

-The angle that the edge of a bead of water makes with the surface of the contact lens -The smaller the angle the better the wettability

Question 26

Difference between cleaning and disinfecting

Answer 26

Cleaning removes debris and deposits Disinfecting kills bacteria and pathogens

Question 27

Four methods of contact lens care systems

Answer 27

-Chemical -Hydrogen peroxide -Thermal -Ultraviolet

Question 28

Parameters to determine if a patient is a good contact lens candidate

Answer 28

-Motivation -Occupation -Lifestyle -Ocular history -General health -Medications -Age/ maturity

Question 29

Questions to ask a current contact lens wearer

Answer 29

-How long have they been wearing CL? -How long since last CL check? -How often replace lenses? -How old is current pair? -What is typical wear time? -How often do they sleep with lenses on? -What solution do they use?

Question 30

Vertex distance

Answer 30

The distance of the lands from the surface of the eyeball -Closer adds minus power -Further adds plus power (So CL must have more plus power)

Question 31

Range of average K values

Answer 31

38.00D-46.00D Higher than 48D is suspicious for keratoconus

Question 32

Average corneal diameter

Answer 32

11.8mm

Question 33

Average soft contact lens diameter

Answer 33

14.5 mm

Question 34

Monovision

Answer 34

Two different contact lenses, distance power on dominant eye, near power on non-dominant eye

Question 35

Modified monovision

Answer 35

Single vision distance power on dominant eye, multifocal lens on non-dominant eye. 

Question 36

Some CL insertion methods

Answer 36

-Directly on cornea -On sclera then slide onto cornea -Slide under upper eyelid for a small aperture 

Question 37

Some CL removal methods

Answer 37

-Pinch off -J stroke -Scissors versus blink

Question 38

Possible lens complications

Answer 38

-Chipped cracked or torn lens -Protein deposits -Scratched GP lens -Mucus film -Lens discolouration

Question 39

GPC

Answer 39

Giant papillary conjunctivitis

Question 40

CLARE

Answer 40

Contact lens acute red eye

Question 41

SPK

Answer 41

Superficial punctate keratitis