Topical Anaesthetics Flashcards
What may we use topical anaesthetics for?
Contact tonometry
Contact lens fitting
Foreign body removal
Gonioscopy
Lacrimal procedures- such as the insertion of punctal plugs
Never for the relief of symptoms
What are the advantages of topical anaesthetics?
Allow certain procedures to be conducted
- Make the patient more comfortable
- Make procedures easier for practitioner
What are the disadvantages of topical anaesthetics?
- Sting (due to pH)
- Delay healing
- Eye is more susceptible to damage
- Repeated instillations
What is the mode of action of topical anaesthetics - how do they reduce sensation?
Topical anaesthetics block sodium channels which mean action potentials cannot be fired causing that loss of sensation.
How do topical anaesthetics travel so rapidly across membranes?
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.
What are the lipid soluble and hydrophilic portions of a topical anaesthetic seperated by?
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”
Which type of anaesthetics have a shorter duration and why?
Ester link topical anaesthetics because an ester link is more readily broken down.
What are examples of ester link topical anaesthetics?
■Oxybuprocaine ■Tetracaine ■Proparacaine
What is an example of an amide link topical anaesthetic?
Lignocaine
When might one chose to use lignocaine over an ester topical anaesthetic?
If px has displayed previous allergy to ester form topical anaesthetic.
What is the most potent ester link topical anaesthetic?
Tetracaine Hydrochloride (Amethocaine)
What would we use Tetracaine Hydrochloride (Amethocaine) for?
It is the most potent - induces deepest anaesthesis - and so we would use it for foreign body removal.
What are the disadvantages of Tetracaine Hydrochloride (Amethocaine)?
Stings the most
Associated with punctate staining
Are px likely to display a sensitivity toward Tetracaine Hydrochloride (Amethocaine)?
Rarely on first time application but may with repeated doses.
What are contraindications of using Tetracaine Hydrochloride (Amethocaine)?
• Sulphonomides • Premature babies • Known allergy • Pregnancy/lactation
In what dose is Tetracaine Hydrochloride (Amethocaine) available and how should it be stored?
0.5 and 1.0% in Minims – Store below 25°C, protect from light – Hydrolysed by light
What is the most widely used topical anaesthetic by U.K. optometrists?
Oxybuprocaine Hydrochloride (Benoxinate) 0.4%
Are sensitivity reactions to Oxybuprocaine Hydrochloride (Benoxinate) common?
No - they are rare!
Why may someone prefer Oxybuprocaine Hydrochloride (Benoxinate) over amethocaine?
Less stinging and irritation
When should one be aware of the bactericidal properties of Oxybuprocaine Hydrochloride (Benoxinate)?
In a hospital setting - you wouldn’t want to use it as the topical anaesthetic you use for goldmann before taking a corneal scrape.
What is a bactericide?
A substance which kills bacteria
What are contraindications of Oxybuprocaine Hydrochloride (Benoxinate)?
• Known allergy • If other eye drops with containing chlorhexidine acetate as a preservative are being used • Pregnancy/lactation • Premature babies
What dose is Oxybuprocaine hydrochloride used in?
Available in Minims 0.4%
True or False - Proxymetacaine Hydrochloride stings the least
True
Why is Proxymetacaine Hydrochloride ideal for goldmann tonometry?
It induces the least corneal punctate staining
True or False- Proxymetacaine Hydrochloride has the least anti-bacterial properties
True - and so is useful for corneal swabs
Is sensitivity to Proxymetacaine Hydrochloride common?
No it is rare
What are contraindication of Proxymetacaine Hydrochloride?
Known allergy Overactive thyroid Heart disease Premature babies Pregnancy/lactation
What dose is Proxymetacaine Hydrochloride available in?
Minims 0.5%
What are the containdications for Lidocaine Hydrochloride (Lignocaine)?
• Pregnancy/lactation • Premature babies
What dose is Lidocaine Hydrochloride (Lignocaine) available in?
Available in Minims 4% combined with 0.25% fluorescein Store below 25°C, protect from light
What are side effects of topical anaesthetics?
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
What can repeated use of topical anaesthetics lead to?
Repeated use —> epithelial toxicity—-> serious keratopathy This can involve: epithelial loss, stromal oedema, corneal infiltrates, anterior chamber reaction
What should one be aware of when using topical anaesthetics?
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
