Topical Anaesthetics

Question 1

What may we use topical anaesthetics for?

Answer 1

Contact tonometry

Contact lens fitting

Foreign body removal

Gonioscopy

Lacrimal procedures- such as the insertion of punctal plugs

Never for the relief of symptoms

Question 2

What are the advantages of topical anaesthetics?

Answer 2

Allow certain procedures to be conducted

• Make the patient more comfortable
• Make procedures easier for practitioner

Question 3

What are the disadvantages of topical anaesthetics?

Answer 3

• Sting (due to pH)
• Delay healing
• Eye is more susceptible to damage
• Repeated instillations

Question 4

What is the mode of action of topical anaesthetics - how do they reduce sensation?

Answer 4

Topical anaesthetics block sodium channels which mean action potentials cannot be fired causing that loss of sensation.

Question 5

How do topical anaesthetics travel so rapidly across membranes?

Answer 5

They contain 2 parts - a lipid soluble hydrophobic portion and a readily ionisable hydrophilic portion (that can switch from uncharged to charged form)

It’s due to the fact that they can be lipophilic and hydrophobic, and charged or uncharged, that enables them to rapidly diffuse across the lipid membrane of the epithelial cells and bind to the intracellular portion of sodium channels.

Question 6

What are the lipid soluble and hydrophilic portions of a topical anaesthetic seperated by?

Answer 6

Either an ester or amide link

“The lipid soluble and hydrophilic portions are separated by an intermediate alkyl chain which contains either an ester or an amide linkage”

Question 7

Which type of anaesthetics have a shorter duration and why?

Answer 7

Ester link topical anaesthetics because an ester link is more readily broken down.

Question 8

What are examples of ester link topical anaesthetics?

Answer 8

■Oxybuprocaine ■Tetracaine ■Proparacaine

Question 9

What is an example of an amide link topical anaesthetic?

Answer 9

Lignocaine

Question 10

When might one chose to use lignocaine over an ester topical anaesthetic?

Answer 10

If px has displayed previous allergy to ester form topical anaesthetic.

Question 11

What is the most potent ester link topical anaesthetic?

Answer 11

Tetracaine Hydrochloride (Amethocaine)

Question 12

What would we use Tetracaine Hydrochloride (Amethocaine) for?

Answer 12

It is the most potent - induces deepest anaesthesis - and so we would use it for foreign body removal.

Question 13

What are the disadvantages of Tetracaine Hydrochloride (Amethocaine)?

Answer 13

Stings the most

Associated with punctate staining

Question 14

Are px likely to display a sensitivity toward Tetracaine Hydrochloride (Amethocaine)?

Answer 14

Rarely on first time application but may with repeated doses.

Question 15

What are contraindications of using Tetracaine Hydrochloride (Amethocaine)?

Answer 15

• Sulphonomides • Premature babies • Known allergy • Pregnancy/lactation

Question 16

In what dose is Tetracaine Hydrochloride (Amethocaine) available and how should it be stored?

Answer 16

0.5 and 1.0% in Minims – Store below 25°C, protect from light – Hydrolysed by light

Question 17

What is the most widely used topical anaesthetic by U.K. optometrists?

Answer 17

Oxybuprocaine Hydrochloride (Benoxinate) 0.4%

Question 18

Are sensitivity reactions to Oxybuprocaine Hydrochloride (Benoxinate) common?

Answer 18

No - they are rare!

Question 19

Why may someone prefer Oxybuprocaine Hydrochloride (Benoxinate) over amethocaine?

Answer 19

Less stinging and irritation

Question 20

When should one be aware of the bactericidal properties of Oxybuprocaine Hydrochloride (Benoxinate)?

Answer 20

In a hospital setting - you wouldn’t want to use it as the topical anaesthetic you use for goldmann before taking a corneal scrape.

Question 21

What is a bactericide?

Answer 21

A substance which kills bacteria

Question 22

What are contraindications of Oxybuprocaine Hydrochloride (Benoxinate)?

Answer 22

• Known allergy • If other eye drops with containing chlorhexidine acetate as a preservative are being used • Pregnancy/lactation • Premature babies

Question 23

What dose is Oxybuprocaine hydrochloride used in?

Answer 23

Available in Minims 0.4%

Question 24

True or False - Proxymetacaine Hydrochloride stings the least

Answer 24

True

Question 25

Why is Proxymetacaine Hydrochloride ideal for goldmann tonometry?

Answer 25

It induces the least corneal punctate staining

Question 26

True or False- Proxymetacaine Hydrochloride has the least anti-bacterial properties

Answer 26

True - and so is useful for corneal swabs

Question 27

Is sensitivity to Proxymetacaine Hydrochloride common?

Answer 27

No it is rare

Question 28

What are contraindication of Proxymetacaine Hydrochloride?

Answer 28

Known allergy Overactive thyroid Heart disease Premature babies Pregnancy/lactation

Question 29

What dose is Proxymetacaine Hydrochloride available in?

Answer 29

Minims 0.5%

Question 30

What are the containdications for Lidocaine Hydrochloride (Lignocaine)?

Answer 30

• Pregnancy/lactation • Premature babies

Question 31

What dose is Lidocaine Hydrochloride (Lignocaine) available in?

Answer 31

Available in Minims 4% combined with 0.25% fluorescein Store below 25°C, protect from light

Question 32

What are side effects of topical anaesthetics?

Answer 32

 Transient stinging

 Transient blurring

 Conjunctival hyperaemia

 Mild superficial epithelial damage not uncommon, especially with tetracaine

represents local toxicity

 Punctate keratitis

• Systemic reactions rare due to the small quantities of drug involved

Question 33

What can repeated use of topical anaesthetics lead to?

Answer 33

Repeated use —> epithelial toxicity—-> serious keratopathy This can involve: epithelial loss, stromal oedema, corneal infiltrates, anterior chamber reaction

Question 34

What should one be aware of when using topical anaesthetics?

Answer 34

Permeability of epithelium cells increased by instillation of topical anaesthetic

Enhances effect of other drugs

 Patient should be instructed not to rub eye or leave practice until anaesthetic effect has worn off

 Healing of epithelial cells reduced by use of topical anaesthetics