Wk 13 - Ocular Anesthetics

Question 1

Ester-linked Local Anesthetics

Answer 1

Most topical anesthetics.
Locally metabolized by esterase enzymes:
• Shorter duration of action

Categories:
1) PABA
•	Tetracaine
•	Benoxinate
2) MABA
•	Proparacaine
3) Cocaine

Question 2

Amide-linked Local Anesthetics

Answer 2

Most injectable anesthetics
Metabolized only in the liver:
• Longer duration of action

Examples:
Lidocaine

Question 3

Ocular Anesthetic MOA

Answer 3

Sodium channel blockers / Inhibit nocireceptor signal transduction
1. Non-ionized, lipid soluble drug crosses membrane of sensory neuron axon
2. Drug is ionized inside cell
3. Drug blocks Na+ channels to prevent Na+ influx
4. Neuron is unable to depolarize and send sensory signal
5*. If ester-linked, local cellular enzymes break down the drug over time

Question 4

Ocular Anesthetic Duration of Action

Answer 4

Duration of action is proportional to the time length of drug contact with nerve.
Contact time is affected by:
1) Drug structure
• Amide-linked removed less quickly than ester-linked
2) Concentration of solution
• Higher concentration has longer contact time
3) Rate of removal from site
• Slower rate of removal has longer contact time

Question 5

Cocaine

Answer 5

Topical Anesthetic

-Prototype anesthetic drug, but not commercially available due to potential for abuse (schedule II drug)
o Must be compounded at a pharmacy

Cornea effects
o	Onset: 2% sol produces anesthesia in 5-10 min
o	Duration
•	Complete anesthesia for 20 min
•	Incomplete anesthesia for 1-2 hours
Conjunctiva effects
o	Duration: 15-20 min
o	Includes vasoconstriction due to sympathomimetic effects

MOA

1) Blocks neuronal reuptake of norepinephrine to prolong sympathetic effects
- > Mydriasis and vasoconstriction
2) Blocks neuronal Na+ channels
- > Anesthesia

Question 6

Adverse effects of topical Cocaine

Answer 6

1) Corneal damage
• Loosened epithelium
• Grey corneal pitting and irregularities
2) Systemic absorption via mucous membranes
• CNS stimulation
• Elevation of blood pressure
• Avoid in HTN patients

Question 7

Clinical uses of topical Cocaine

Answer 7

1) Debridement of corneal ulcers
• Produces anesthesia and loosens epithelium so that it is easier to remove
2) Diagnosis of Horner’s syndrome
• Fails to dilate the pupil if disease is present

Question 8

Pontocaine (0.5% tetracaine sol)

Answer 8

Onset: 10-20 sec
Duration: 10-20 min

Less comfortable than benoxinate or proparacaine

Side effects
• SPEE/SPK
• Rare allergic reactions

Contraindication: topical sulfonamide therapy
• Interferes with sulfa drug action

Question 9

TetraVisc Forte (high viscosity 0.5% tetracaine sol)

Answer 9

Preparations
• Multi-dose 5 mL bottle
• Unit dose 0.6 mL bottles

Efficacy: similar to Akten (lidocaine 3.5%)

Higher viscosity than standard tetracaine sol
• Increased contact time

Clinical use
• Apply to conjunctival or lid for surgical procedures
• Improves pain levels in post-op patients

Question 10

Benoxinate: Fluress (0.4% benoxinate + 0.25% NaFl)

Answer 10

Benoxinate is only commercially available topically with NaFl
• Bactericidal properties prevent bacterial growth in NaFl sol

Onset, duration, and intensity equal to tetracaine

Clinical use: Goldmann tonometry

Side Effects
• SPEE with epithelial desquamation
• Rare allergic reaction

Question 11

Proparacaine 0.5% sol (Alcaine, Ophthaine, Ophthetic)

Answer 11

Most comfortable of the topical ocular anesthetics

Clinical use: General ophthalmic anesthesia

Onset, duration, and intensity similar to tetracaine

Side effects (rare)
•	Mild stromal edema
•	SPEE and epithelial stippling
•	Conjunctival hyperemia and chemosis
•	Lid edema

Question 12

Fluorocaine (0.5% proparacaine + 0.25% NaFl sol)

Answer 12

Clinical use: Goldmann tonometry

o Less commonly used than Fluress

Question 13

Akten (PF 3.5% lidocaine gel drop)

Answer 13

Increased duration of effect
• Viscous gel formula
• Amide-linked

Clinical use: Ocular surface anesthesia during ophthalmologic procedures

Apply 2 drops to ocular surface in area of planned procedure
o Onset: 20-60 sec
o Duration 5-30 min

Question 14

Lidoderm (5% lidocaine patch)

Answer 14

Apply to intact skin for treatment of post-herpetic neuralgia

Question 15

EMLA cream or patch (2.5% lidocaine and 2.5% prilocaine)

Answer 15

o Treats post-herpetic neuralgia

o Pre-op treatment for removing benign skin lesions

Question 16

Choosing a topical ophthalmic anesthetic

Answer 16

All have similar
o Onset (15-30 sec)
o Duration of maximum effect (15-20 min)
o Duration of incomplete effect (45-60 min)
• So choose the drop that is most comfortable and has the fewest side effects for your patient
• If patient has a hypersensitivity reaction to one drug, switch to a different class
-Ex. Patient reacts to tetracaine, which is a PABA drug, switch to proparacaine, since it is MABA

Question 17

Topical Anesthetic Adverse Effects

Answer 17

Topical drops have fewer side effects than injectable anesthetics but are More likely to have local side effects than systemic
1) Local irritation
o Mild burning and redness that quickly resolve
• Rare hypersensitivity
• Systemic effects
2) Nervousness, tremors, convulsions, depressed CNS (reduced breathing, loss of consciousness)
o No reported cases of serious systemic reactions to a topical anesthetic
3) Induced corneal syndrome
o Occurs within 6 days to 6 weeks of prolonged topical anesthetic use
• Never Rx a patient a topical anesthetic or allow a patient to self-administer one
o Usually patients with medical, paramedical, or welding backgrounds
o Drugs inhibit healing of cornea and produce loss of epithelium
o Corneal stromal ring
• DDx: acanthamoeba
o Conj hyperemia
o Treatment
• Discontinue anesthetic use
• 1% atropine bid for pain
• Apply pressure patch with analgesic and prophylactic antibiotic if epithelial damage warrants

Question 18

Topical Anesthetic Precautions

Answer 18

o Limit dosage and concentration of drug and frequency of use
o Administer to seated or recumbent patient in case of fainting
o Depress puncta and use sparingly with conjunctival hyperemia to limit systemic absorption
o Increase duration of effect by using soaked cotton swab or pledget for greater contact time

Question 19

Use of Topical Anesthetic for RGP Fitting

Answer 19

Studies show that using a topical anesthetic while fitting an RGP
o Does not cause more epithelial damage than saline
o Reduces time needed to obtain and analyze NaFl pattern
o Allows for more patient comfort

Question 20

Injectable Anesthetics

Answer 20

Lidocaine

Indications
•	Tissue infiltration
o	Benign lid lesion excision
o	Chalazion excision
o	Laser photocoagulation to treat trichiasis
o	Argon laser punctoplasty
•	Facial nerve block
•	Retrobulbar nerve block

Added epinephrine
• Causes vasoconstriction to:
o Prolong duration of anesthesia
o Decrease systemic absorption
o Decrease bleeding
• Concentration: 1:50,000 to 1:200,000
o 1:100,000 is most common
• Avoid use in nerve blocks due to side effects
• Avoid contact with fingers/nose due to vasoconstriction
• Side effects: tachycardia, hypertension, headaches

Question 21

Lidocaine (Xylocaine)

Answer 21

Be most familiar with this local injectable
• Onset: 4-6 min
• Duration: 40-60 min, 120 with epinephrine