7 - Anasthetics and stains Flashcards
what is a topical anaesthetic
POM
- drugs that reversibly block transmission in sensory nerves
indications for use ?
- contact tonometry
- cl fitting
- foreign body removal
- gonioscopy
- lacrimal procedures
- ever for release of symotoms
advantages of local anaesthetics
- allow certain procedures to be conducted
- make px more comfortable
- makes procedure easier for practitioner
disadvantages of local anaesthetic
- sting (due to pH)
- delay healing (reduces production of collagen)
- eye is more susceptible to damage
what is the mode of action of local anaesthetics
memorise action potential graph + process
- action potential passes along nerve
- successive depolarisations and repolarisations of adjacent areas
topical anaesthetics reversibly block nerve conduction by blocking sodium channels, therefore action potential cannot be generated
what are local anaethetics made of
lipid soluble hydrophobic portion
and a readily ionised hydrophillic portion
they can swtich from charged and unchargedh
what does being hydrophobic and lipophillic allow them to to
rapidly diffuse across lipid membrane of the epithelial cells and bind to the intracellular portion of sodium channels
what are the different portions separated by
- intermediate alkyl change
which contains either an ester or amide linkage
chemical structure of anesthetics
ESTER LINK
- hydrolysed by cholinesterase
- short duration
- oxybuprocaine
- tetracaine
- proparacaine
chemical structure of local anaesthetics
AMIDE LINK
- resistant to hydrolysation
- longer duration
Lignocaine only
which structure are allergic reactions more common in
esters
which linkage bond is broke more easily
ester
what is the onset of all anaesthetics
1 min
15 mins duration
- oxybuprocaine
- proxymetacaine
20 mins duration
tetracaine
30 min duration
lidocaine
which anaesthetic is most potent
tetracaine hydrochlride (amethocaine)
stings most
- provides deepest anaesthesia
- foreign body removal
sensitivity is rare but occurs after repeated doses
- associated with punctate staining
contraindications/caution of tetracaine hcl
- prematue babies
-known allergy - sulphonomides
- prenancy/lactation
preparations of tetracaine hcl
0.5% and 1% in minims
- store below 25 and protect from light
- hydrolysed by light
- solutions >1% damage cornea
removal of foregin body after 1 drop
which is most commonly used by optoms
oxybuprocaine hydrochloride (benoxinate)
- less stinging and irritation than amethocaine
- bactericidal properties (disadvantage)
what are contraindications/cautions of oxybuprocaine
- known allergy
- premature babies
- pregnancy/lactation
- if px is on any other drops containing chlorohexidine acetate as a preservative are being used
preparations of oxybuprocaine hcl
- minims 0.4%
- store below 25 protect from light
opthalmology
- 3 drops over 5 min interval allows foreign body to be removed
which one stings least
Proxymetacaine HCL
- ideal for tonometry, minimal punctate corneal staining
- least antibacterial properties
contraindications/caution of proxymetacine hcl
- known allergy
- overactive thyroid
- heart disease
- premature babies
- pregnancy/lactation
preparations of proxymetacine hcl
minims 0.5%
stored 2-8C, fridge
can be used in cataract extraction as vert potent
Lidocaine HCL (lignocaine
- stings less than amethocaine
-amide link - used if px sensitive to ester link - longer duration
contraindications/caution
- pregnancy/ lactation
- premature babies
lidocaine hcl preparations
- minims 4% combined with 0.25% fluoroscien
side effects of lidocaine
- transient stinging/bluring
- conjunctical hyperaemia
- mild superficial epithelial damage
- ## punctate keratitis
repeated use ~ epithelial toxicity ~ serios keratopathy
uses + disadvantages of Fluoeoscien
- tonometry
- corneal abrasions
- CL fitting
- TBUT
- lacrimal drainage
psuedomonas aeruginosa
rose bengal uses + disadvantages
- staining od fead and devitalised cells
-aids dry eye diagnosis
irritates try eyes on instilation
stings
can stain healthy cells
uses and disadv of lissamne green
- stains lipid like structures
no disadvantages
why is fluoro not a true stain
just colours tear film.
epithelial damage means fluoro can gain access to deeper layers
contrainidications of fluoro
- known sensitivity
- soft CL lenses
cautions of fluoro in a multi dose bottle
-contamination problems in hospitals in 1950s
- fl used on damaged corneas
- psuedomonas has affinity for it
progesses rapidly
corneal perforation 48h
fluoro minims
1 and 2%
contains buffer to stabilise solution
slighty alkaline
