unit 6

Question 1

Why wear contact lenses

Answer 1

refractive correction
cosmetic or theatrical purposes
bandage
keratoconus

x-chrom and chromagen lenses for red-green colour dificiency
sports lenses
dry eye
photochromic lenses
drug delivery

Question 2

Contact Lens Materials

Answer 2

Hard lenses
- PMMA, GP
soft lenses
-hydrogel, silicone hydrogel
hybrid lenses

Question 3

Hard lenses- PMMA

Answer 3

PMMA (polymethyl methacrylate)
- plexiglass or acrylic lenses
- very durable lens but not oxygen permeable
- small diameter in order to allow cornea to “breathe”/tear flow
- 1% wearers

Question 4

Soft lenses- Hydrogel

Answer 4

(hydroxyethyl methacrylate or HEMA)

  -flexible lens that binds with water to create a hydrophilic lens
  -can be worn occasionally 
  - coloured
  - easy to fit/stable
  -more comfortable due to higher water content

Question 5

Hard lenses- GP

Answer 5

(gas permeable)
- RGP or rigid gas permeable
- silicone made lenses oxygen permeable than PPMA
- vision better than soft lenses
-more comfortable
- 10%

Question 6

Soft lenses- Silicone Hydrogel

Answer 6

(SiHy)
- silicone into the material made the lens more “breathable”
- increase in overnight lens wear
- can be worn occasionally
-coloured
-more stable, easier to handle due to lower content than HEMA

Question 7

Hybrid lenses

Answer 7

“best of both worlds”

• clear and crisp vision from the GP lenses
  -comfortable “skirt” made of silicone hydrogel compared to soft lense

-easier to remove
-visually more stable than soft toric lenses
but limited ability to customize

Question 8

Contact Lens Designs (5)

Answer 8

spherical lenses
vs
toric lenses

multifocal lenses
monovison
lenticular lenses

Question 9

Spherical lenses

Answer 9

one lens power to correct myopia or hyperopia
same lens thickness throughout
can move around

Question 10

Toric lenses

Answer 10

mutluple power in lens to correct astigmatism
lens is stabilzed in one position through eyelid interaction with lens
markings help CL fitter assess lens orientation

Question 11

Multifocal lenses

Answer 11

multiple powers in lens to correct distance and near
aspheric lens design(surface gradually flatters from the center-out)
centre-distance or centre-near depending on manufacturer

Question 12

Monovision

Answer 12

distance power in one eye, near power in the other eye
good option for high astigmatism
depth perception is compromised
only works with low add power

Question 13

lenticular lenses

Answer 13

used for aphakic patients
has a sharply defined transition between carrier and prescription zone

Question 14

Soft contact lens care

Answer 14

only use contact lens solutions for soft lenses
ALWAYS wash hands before touching eyes/handing lenses
ALWAYS rub, even if its not a rub formula
be careful when using a hydrogen peroxide system
change lenses at appropriate time intervals
DO NOT over wear lens

Question 15

GP contact lens care

Answer 15

only use contact lens solutions for GP lenses
ALWAYS wash hands before touching eyes/handing lenses
RUB in BACK and FORTH motion or from centre to edge all the way around
DO NOT rub in circular motion
protein removers might be needed
lenses can be polished to remove deposits are scratches

Question 16

Cleaning lens cases

Answer 16

lens cases must be cleaned regularly
DAILY
WEEKLY
replace every 2-3 months
-or good to buy new case when the solution runs out

Question 17

Fitting Parameters

Answer 17

Base curve
diameter
center thickness
edge design
oxygen transmissibity
water content
sagittal depth
wetting angle

Question 18

base curve and center thickness

Answer 18

base curve
- curvature of the posterior surface of the lens is matched to the curvature of the anterior surface of the cornea
- mm of radius of of curvature
- corneal base curve is measured with a keratometer in diopters
- higher the number=flatter the lens

Center thickness
- the distance in mm from surface of the lens to the back surface
- high plus power lenses will have a thicker center thickness than a high minus power lens

Question 19

Diameter

Answer 19

• maximum edge to edge width of lens, measured in mm
• determined by lens type and patients horizontal vision iris diameter (HVID)
• hard lenses are smaller than HVID
• soft, hybrid and scleral lenses are larger than HVID

Question 20

edge design

Answer 20

need of good edge design:
- proper tear flow under lens
- proper blink interaction with eyelids
- optimal wearer comfort

must be round of beveled to achieve ideal lens edge design
plus lenses are thinner in the periphery
minus lenses are thicker at the periphery

Question 21

Contact lens complications

Answer 21

1-lens complications
2-solution reactions
3-ocular complications

Question 22

lens complications

Answer 22

chipped, cracked or torn lens
protein deposits
scratched GP lens
mucus film
lens discolouration