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Eye disease and therapeutics > Topical anaesthetics > Flashcards

Topical anaesthetics Flashcards

1
Q

Role of topical anaesthetics

A

Drugs that reversibly block transmission in
sensory nerves

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2
Q

What type of medicines are topical anaesthetics

A

POM (Prescription only medicine)

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3
Q

What are topical anaesthetics most commonly used for

A

Golmann tonometry

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4
Q

Uses of topical anaesthetics

A
  • Contact tonometry
  • Contact lens fitting
  • Foreign body removal
  • Gonioscopy = anterior eye
  • Lacrimal procedures e.g. insertion of punctal plugs which prevents drainage
  • Never for the relief of symptoms
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5
Q

Why shouldn’t you use topical anesthetics for treating and relieving symptoms

A
  • Cause healing is delayed in eye that is already compromised
  • It should be treated by antibiotics or foreign body removal, shouldnt avoid the pain.
  • If use anesthesia for this, can cause keratitis which can lead to nucleation
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6
Q

Advantages of topcial anaesthetics

A
  • Allow certain procedures to be conducted
  • Makethepatient more comfortable
  • Make procedures easier for practitioner
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7
Q

Disadvantages of topcial anaesthetics

A
  • Sting(due to pH)
  • Delay healing because produces reduction in collagen
  • Eye is more susceptible to damage
  • Repeated instillations
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8
Q

What is pH of topical anaesthetics and eye

A

-Topcial anaesthetic = 3.5 - 5.5
- Eye = 7

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9
Q

How many drops needed for topical anaesthetic

A

1

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10
Q

How do topical anaesthetic work - mode of action

A
  • Sensory information passes along nerve fibres via electrical impulses (action potentials)
  • Nerve has negative charge at rest
  • Action potential is generated by influx of sodium ions into the nerve
  • Results in positive charge (depolarisation)
  • Efflux of potassium ions returns nerve to resting potential i.e repolarization
  • Action potential passes along nerve
  • So get successive depolarizations and repolarizations of adjacent areas
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11
Q

Role of topical anaesthetic

A

Reversibly block nerve conduction by blocking sodium channels therefore action potential can’t be generated

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12
Q

Structural features of local anaesthetic

A
  • Has 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
  • The lipid soluble and hydrophilic portions are separated by an intermediate alkyl chain which contains either an ester or an amide linkage
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13
Q

What allows the local anaesthetic to rapidly diffsue across lipid membranes of epithelial cells and bind

A

Cause they can be lipophilic and hydrophobic, and charged or uncharged,

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14
Q

Differences between ester link and amide link

A

Ester link:
- Hydrolysed by cholinesterase
- Short duration = so ester linkage broken more easily than amide bond

Amide link:
- Resistant to hydrolysation
- Longer duration

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15
Q

Examples of ester link

A
  • Oxybuprocaine
  • Tetracaine
  • Proparacaine
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16
Q

Examples of amide link

A

Lignocaine

17
Q

What is common in esters

A

Allergic reaction

18
Q

Onset of topical anaesthetic

A

1 minute

19
Q

Duration of topical anaesthetic

A

Amethocaine = 20 mins
Benoxinate = 15 mins
Proxymetacaine = 15 mins
Lignocaine = 30 mins

20
Q

Features of Tetracaine Hydrochloride (Amethocaine)

A
  • Most potent
  • Stings the most
  • Provides deepest anaesthesia = so useful for foreign body removal
  • Sensitivity is rare but occurs after repeated doses
  • Associated with punctate staining due to stinging aspect of pH level

Contraindications/Cautions:
- Px’s taking sulphonomides
- Premature babies
- Known allergy
- Pregnancy/lactation

21
Q

Preparations of Tetracaine Hydrochloride (Amethocaine)

A

– 0.5 and 1.0% in Minims
– Store below 25°C
- Protect from light cause the chemical structures are hydrolysed by light so drug will become damaged
– Solutions >1% damage cornea

22
Q

Role/use of Tetracaine Hydrochloride (Amethocaine)

A

Removal of foreign body = possible after instillation of one drop

23
Q

Features of Oxybuprocaine Hydrochloride (Benoxinate)

A
  • Most widely used topical anaesthetic by Optometrists in UK
  • Sensitivity reactions rare
    -Less stinging, irritation than amethocaine
    -Bactericidal properties

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

24
Q

What is the most widely used topical anaesthetic by Optometrists in UK

A

Oxybuprocaine Hydrochloride (Benoxinate)

25
Q

Preparation of Oxybuprocaine Hydrochloride (Benoxinate)

A
  • Available in Minims 0.4%
  • Store below 25°C, protect from light
26
Q

How many drops needed in Oxybuprocaine Hydrochloride (Benoxinate)

A

Three drops instilled over five minute interval

27
Q

Use of Oxybuprocaine Hydrochloride (Benoxinate)

A

Allows foreign body to be removed

28
Q

How long does it take to recover from Oxybuprocaine Hydrochloride (Benoxinate)

A

Corneal sensation recovers after one hour

29
Q

Features of Proxymetacaine Hydrochloride

A
  • Stings the least
  • Minimal punctate corneal staining
  • Ideal for tonometry
  • Least antibacterial properties
  • Useful when taking conjunctival swabs

Contraindications/Cautions:
- Known allergy
- Overactive thyroid
- Heart disease
- Premature babies
- Sensitivity rare

30
Q

Preparations of Proxymetacaine Hydrochloride

A
  • Minims 0.5%
  • Store 2-8C, have to keep in a
    dedicated refrigerator
31
Q

How many drops used in Proxymetacaine Hydrochloride

A
  • 1 drop every 5 – 10 minutes
  • 5 - 7 drops in total
32
Q

Disadvantage of Proxymetacaine Hydrochloride

A

Very potent

33
Q

Use of Proxymetacaine Hydrochloride

A

Can be used in cataract extraction

34
Q

Features of Lidocaine Hydrochloride (Lignocaine)

A
  • Stings less than amethocaine
  • Amide link
  • Used when patients sensitive to ester link
  • Longer duration

Contraindications/Cautions:
- Pregnancy/lactation
- Premature babies

35
Q

Preparations of Lidocaine Hydrochloride (Lignocaine)

A
  • Available in Minims 4% combined with 0.25% fluorescein
  • Store below 25°C, protect from light
36
Q

Side effects of anaesthetics

A

-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
- Hypersensitvity reactions, though these are less likely with lidnocaine due to amide link,can range from mild transient blepharoconjunctivitis to diffuse necrotising epithelial keratitis
- Necrotising keratitis incidence ~1/1000 with ester drugs
- Repeated use = epithelial toxicity = serious keratopathy
- This can involve: epithelial loss, stromal oedema, corneal infiltrates, anterior chamber reaction

37
Q

Precautions of anaesthetic drugs

A
  • 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
  • Open to abuse
  • Usually by health care practitioners
  • Young children

Eye disease and therapeutics (9 decks)

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