unit 3 - contact lenses

Question 1

What are the complications of contact lens use?

Answer 1

Deposits
Infection
Discolouration

Question 2

What types of deposits can build up when using contact lenses?

Answer 2

Cosmetics
Cations
Dust
Lysozyme film
Tear proteins
Oils

Question 3

What can contact lens deposits cause?

Answer 3

Allergy
Irritation
Reduced visual acuity
Discoloration
Reduced antimicrobial activity of solutions

Question 4

What can contact lens deposits lead to?

Answer 4

Conjunctivitis
Keratitis
Corneal ulceration

Question 5

What can cause infections when using contact lenses?

Answer 5

Lens
Lens case
Lens solution

Question 6

Give examples of organisms that can cause infections when using contact lenses

Answer 6

Bacterial
- Pseudomonas aeruginosa
- Staphylococcus aureus
- attaches to surface of lens
- can lead to corneal ulceration

Fungal
- Candida albicans
- Fusarium solani
- can penetrate soft lenses to infect the cornea
- patient complains of irritation and blurred vision

Acanthamoeba
- rare but serious infection by protozoa
- found in water
- tap water
- swimming
- causes irreversible keratitis

HIV/vCJD
- very unlikely
- potential infection route through trial sets

Question 7

What can cause discolouration of contact lenses?

Answer 7

Local/systemic drugs
- rifampicin
- sulphasalazine
Tobacco
Cosmetics
Buffering agents
- sorbic acid

Question 8

How should contact lenses be looked after?

Answer 8

Lenses accumulate secretions from
- eye
- substances from fingers
- cosmetics
Should be cleaned daily
- immediately following removal
- disinfected nightly
- daily disposable soft lenses don’t need cleaning
- hygiene still important
Cases should also be cleaned regularly
Don’t top up solutions in cases
- replace each time

Question 9

How can contact lenses be cleaned?

Answer 9

Clean after every use to remove deposits
- grease
- cosmetics
Cleaning also improves disinfection
Wash hands!
Surfactant and mechanical friction in palm of hand
- rinse with saline
Enzymatic cleaner also recommended to remove protein deposits
- weekly

Question 10

What does multi-purpose contact lens solution contain?

Answer 10

Surfactant and disinfectant
One bottle
- more convenient
Still need to clean before disinfecting
- use MPS to rub and rinse
No-rub formulations now available
- studies suggest poorer disinfection
Not generally as effective as separate surfactant

Question 11

What is saline used for in cleaning contact lenses?

Answer 11

Used for rinsing/cleaning lens case
Solvent for enzyme tablets
Aerosols and squeezable bottles
Some bottles contain preservatives
- NOT sufficient for disinfection of lenses

Question 12

How are contact lenses disinfected?

Answer 12

Heat
- can ‘bake on’ deposits
- not for RGP and high-water soft lenses

Chemical
- easier
- cheaper
- portable
- can combine with cleaners
- MPS

Oxidative
- hydrogen peroxide
- faster than chemical
- preservative-free

Question 13

What is the purpose of disinfectant lens solutions?

Answer 13

Needed to decrease microbial contamination
Should have wide range of antimicrobial activity
Must be
- sterile
- chemically stable
- non-irritant
- isotonic
Must comply with Medical Device Directive
- CE mark

Question 14

How is hydrogen peroxide used to clean contact lenses?

Answer 14

Efficacious at 3%
- good vs acanthamoeba
Must neutralise before reinsertion
Two steps
- soak in peroxide
- overnight
- neutralise
- 10-20 mins
One step
- peroxide and neutraliser
- time release catalase tablet or platinum coated disc

Question 15

How should contact lenses be stored?

Answer 15

Fully submerged in solution in clean plastic case

Question 16

Why is wetting contact lenses important?

Answer 16

For RGP lenses, increases comfort and makes reinsertion easier
- polyvinyl alcohol-based “comfort drops”