3.1.10 Uses diagnostic drugs to aid ocular examination. Flashcards
Mydriatics: Using different concentrations
- Darker irides require higher concentration as they have more melanin e.g. 1.% tropicamide. Lighter irides can get away with 0.5% or 1%. More melanin means the drug binds to it more & so less is absorbed, hence the need for higher concentration.
- Remember: more drops/concentration used may mean longer effect of drug of up to 18 hours for tropicamide.
Mydriatics: INDICATIONS
- Small pupils
- Dense cataracts
- Diabetic screening
- Retinal detachment symptoms/signs
- Unexplained vision loss/pain etc
Mydriatics: CONTRAINDICATIONS
-
Hypersensitivity to drug or any component of the preparation.
- Minims Contain: Each Minims unit contains approximately 0.5 ml eye drops solution of tropicamide 0.5% w/v (2.5 mg) or 1% w/v (5 mg). The other ingredients are sodium hydroxide and hydrochloric acid (for pH adjustment) and purified water.
- Mydriacyl Contains: tropicamide 0.5% or 1%. Preservative: benzalkonium chloride 0.01%. Inactives: sodium chloride, edetate disodium, hydrochloric acid and/or sodium hydroxide (to adjust pH), purified water; pH range 4.0-5.8.
- Specific medications - no listed medical contra-indications (C/I) specific for the use of tropicamide eye drops, other than a known allergy.
-
Suspected angle closure - probability of induced attack is 0.06-0.09%
- Narrow chamber angles (< grd 2) - more likely in age >60 & high hypermetropia
- Iris-mounted IOLs (regular lens IOLs AOK) - otherwise it can dislocate?
- Multidose preparations contain benzalkonium chloride and should not be used when soft contact lenses are worn as it discolours them. Contact lenses should be removed prior to application and the patient should wait at least 15 minutes before re-insertion
- Cautioned against pregnant women
- Px needs to drive/operate heavy machinery etc afterwards
Mydriatics: SIDE EFFECTS:
- transient stinging
- transient blurring - especially at near - slight effect on ciliary muscles
- photophobia
- raised intraocular pressure
- Following instillation - hyperaemia, oedema, conjunctivitis, dry mouth, CNS disturbances
Tropicamide Hydrochloride is a…
- Store below 25°C (Mydriacyl at 2–8°C).
- Protect from light.
- Antimuscarinic
LEGALITIES
- Access: POM: For use and supply by all optometrists.
- Use:
- Mydriacyl: eye drops, 1.0% tropicamide hydrochloride (Alcon Eye Care Ltd)
- Minims Tropicamide: eye drops, 1.0% tropicamide hydrochloride (Bausch & Lomb UK Ltd) (MOST COMMONLY USED). Also in 0.5%
- Mydriasert: ophthalmic insert for pre-operative mydriasis, 0.28mg tropicamide, 5.4mg phenylephrine (Thea Pharmaceuticals Ltd)
- Supply: Can be supplied by Optometrist with strict caution
- RARELY: “If you have uveitis that affects the front of your eye (anterior uveitis), you may be given mydriatic eyedrops as well as steroid medicine. These eyedrops enlarge (dilate) your pupils and relieve pain by relaxing the muscles in your eye. They can also reduce your risk of developing glaucoma, which affects vision.” - NHS
Pathway for Tropicamide: (Assessor may ask this)
- Antimuscarinic - Block (antagonise) the receptor
- Muscarinic receptors are part of parasympathetic nervous system - functions to conserves the body’s natural activity
- Tropicamide is a non-selective muscarinic antagonist that binds to all subtypes of muscarinic receptors, located at neuromuscular junctions (between motor neuron nerve & its muscle fibre). By binding to muscarinic receptors, tropicamide relaxes the pupillary sphincter muscle and causes pupil dilation. By blocking the muscarinic receptors of the ciliary body, tropicamide also prevents accommodation.
- Reversibly blocks the action of acetylcholine at the post synaptic receptor
Anaesthetic: INDICATIONS
- Diagnostic Procedures
- Contact tonometry
- Gonioscopy
- (Certain) Schirmer tests
- Superficial foreign body removal
- Impressions for scleral contact lenses
- RGP insertion
- Insertion of punctal plugs; lacrimal syringing
Anaesthetics: CONTRAINDICATIONS
- Known hypersensitivity (ester/amide)
- Avoid in premature infants because of the immaturity of the enzyme system that metabolises ester-type local anaesthetics.
- Proxymetacaine should be used cautiously and sparingly in patients with known allergies, cardiac disease or hyperthyroidism because of the increased risk of sensitivity reactions.
- Protect the eye from foreign bodies and rubbing during the period of anaesthesia (up to 30 minutes). Ideally the patient should not leave the practice until corneal sensation has returned.
- No well-controlled clinical trials have been conducted in pregnant or breast-feeding patients, therefore do not use unless considered essential.
Anaesthetics: Side effects
- Minor effects:
- Conjunctival hyperaemia
- Mild punctate keratitis - whitish spots in cornea/grey ground-glass appearance
- Transient blurred vision
- Stinging/burning sensation
- Decreased tear secretion - dryer eyes- Inhibition of blink reflex - eye more vulnerable to trauma
- Reaction at corneal epithelium - loss of epithelial cells, may drop VA to 6/60 but resolves spontaneously (lubricants can help)
- Severe reaction - melting cornea. Antibiotic prophylaxis needed
- Delayed wound healing
- IOP can be affected (lower) - must be measured after insertion
Know what stings the most & the least
- Least = Proxymetacaine
- Then Oxybuprocaine
- Then Lidocaine
- Worst is Tetracaine
Know different onset times
- Proxymetacaine quickest.
- Drugs last for around 30 minutes.
Proxymetacaine Hydrochloride 0.5%
- Onset within 30 seconds, lasts 15 mins
- Most commonly used
- Stored at 2-8 degrees
- Protect from light
- Ester-linked
- Least antibacterial action
Oxybuprocaine Hydrochloride 0.4%
- Onset around 1 minute
- Widely used for applanation
- Store below 25 degrees
- Ester-linked
Lidocaine Hydrochloride 4%
- Less chance of adverse corneal reaction
- Minims Lidocaine and Fluorescein: eye drops, 4% (40mg/ml) lidocaine hydrochloride, 0.25% fluorescein (Bausch & Lomb UK Ltd)
Tetracaine Hydrochloride (Amethocaine) 0.5% & 1%
- Not widely used in Optometry
- Minims Tetracaine: eye drops, 0.5% tetracaine hydrochloride (Bausch & Lomb UK Ltd)
- Minims Tetracaine: eye drops, 1% tetracaine hydrochloride (Bausch & Lomb UK Ltd)
LEGALITIES: Anaesthetics
- Access: POM (prescription only medication): For use by all optometrists.
- Use: Minims Proxymetacaine: eye drops, 0.5% proxymetacaine hydrochloride (Bausch & Lomb UK Ltd). Single use (preservative free)
- Supply: CANNOT be sold/supplied for outside use due to potential of misuse resulting in severe side effects like advanced keratopathy
Pathway for Anaesthetic (Assessor may ask this):
- Site of action is nerve cell membrane, preventing nerve impulses in the cornea, which otherwise feel pain & touch. The drug blocks influx of Na+ into the nerve cell membrane, stopping depolarisation which is key for action potentials to rise & hence the nerve to function.
- Since the corneal nerves are so small, the drug works much quicker & more effectively than other body parts, requiring stronger dosages.
- Neural blockade order: Pain —> Touch —> Temperature —> Pressure —> Motor (paralysis)
- All these receptors get blocked in this order
- The drug is either Amide or Ester linked. The only amide anaesthetic we might use is lidocaine.
- Ester is rapidly broken down, so short duration of action - 20-30 mins duration, onset 1 min
- Lidocaine resistant to break down, so longer action hence used in cataract surgery for example - 30-60 mins duration, onset 1 min
Tropicamide (POM) 0.5% or 1% minims?
College guidelines state MUST use 1% solution when investigating new onset flashes and floaters.
It is an anti-muscarinic drug which causes mydriasis by relaxing the iris sphincter muscle, creating a quick dilation reaction & a pupil which is resistant to bright lights.
Effects
Dilation should be achieved in 20 minutes (2-3 mm) and effects can be expected to last anything up to 4-8 hours.
Possible side effects include angle closure (check IOPs and AC angle before and after dilation).
Contraindications = known allergy to the drug, iris supported IOL, px needing to drive immediately after exam.
Phenylephrine (POM)
Sympathomimetic (alpha-1 adrenergic) drug which causes mydriasis by contracting the iris dilator muscle. This produces a slower reaction (30 mins) and the pupil is still light sensitive.
Effects last 12-24 hours, and the drug stings more on instillation.
2.5% is normally used routinely as 10% gives no more pupil dilation but increases the risk of cardio-vascular side effects.
Cyclopentolate (POM) 0.5% or 1%
Anti-muscarinic with a similar mechanism of action to tropicamide.
Always ensure the px knows how long the drug effects are expected to last, what activities not to do in that time, and emergency protocol in case of adverse reaction. Ideal to give px college information leaflet
Anaesthetics
3 of the 4 main topical ocular anaesthetics are esters, meaning that if you have a reaction to one you will likely have a reaction to all (oxybuprocaine, tetracaine, proxymetacaine).
In this case, lidocaine should be used as it has a completely different mechanism of action (benzoic acid amide).
Oxybuprocaine 0.4% is a p-aminobenzoic acid ester and does not require refrigeration.
Proxymetacaine 0.5% is an m-aminobenzoic acid ester, which should be kept refrigerated as it is unstable at room temperature
Lidocaine 4% is a benzoic acid amide and is available in a solution with fluorescein. It does not require refrigeration. It is much stingier than esters on instillation!
Lidocaine is hydrolysed and metabolised more easily, so it acts quicker, less chance of reaction (metabolise that caused the reaction)
All of the above are expected to cause adequate surface anaesthesia within 2 minutes, which lasts around 30 minutes. They are not a common cause of ADRs, and any allergy should resolve in an hour. Repeated instillations could be toxic and cause diffuse SPK and discomfort. Should resolve in 24 hours
Not rubbing eye – abrasion risk
Proxy stings the least
Desquamation – epithelium peels and melts
