3.1.10 Uses diagnostic drugs to aid ocular examination Flashcards
What is required to note down when instilling a drug?
- Drug
- Dosage
- Date
- Time
- Batch number
- Expiry date
- Disposal
What are mydriatics and what are the two types?
Drugs which dilate the pupil to facilitate the examination of the eye, principally the central and
peripheral fundus but also the lens and vitreous.
* Two Pharmacological Groups: Anti-muscarinic & Sympathomimetic
Describe anti-muscarinics to diate pupil?
- Act on the parasympathetic innervation of the ciliary body and sphincter pupillae (POM).
- Block the muscarinic receptor by preventing the binding of the ACh (post synaptic membrane) at
the ciliary body and sphincter and producing an action potential invoking a response. - Competitive antagonist for Ach, it doesn’t interact with ACh or affect its synthesis,
- Produces both Cycloplegia and Mydriasis
Anti-muscarinics are reversed with use of Pilocarpine (parasympathomimetics).
Describe sympathomimetic to dialte pupil?
Mydriasis: Sympathetic nervous system stimulation causes the radial muscles to contract.
* Receptor: Adrenergic (Alpha - 1)
* Neurotransmitter: Noradrenaline
What are the risks of using mydriatics?
Practical risk in driving and operating heavy machinery post dilation.
o Advise sunglasses due to glare.
o concern of inducing an ACG attack (1/5000) but often the risks of not dilating outweigh
risks of dilating (VH and IOP).
* ACG is most likely to occur during the recovery phase of dilation whereby the mid
dilated pupil in close apposition to anterior surface of the lens can impeded
aqueous outflow.
Advise on Symptoms of ACG:
§ Haloes around lights
§ painful red eye
§ nausea
What are examples of parasympathetic antimuscarinis and example of sympathomimetic?
Parasympathetic antimuscarinics:
* Tropicamide
* Cyclopentolate
Sympathomimetic:
* Phenylephrine
How do you minimise the risk of ACG after mydriasis? What advice should be given?
IOP Pre and Post-Dilation
* Carry out tonometry before and after mydriasis.
* An increase in pressure (>5mmHg) is considered significant or an asymmetric rise
in IOP. Monitor to see if pressures stabilise or decrease after some time.
* If persistent increase then refer to local HES (A&E).
Check Angles
* Mydriasis is contraindicated if anterior chamber angles are very narrow.
* Van Herricks Grade 2 and 1 consider at risk.
* Narrow angles should be investigated by specialist with gonioscopy.
Advice:
* Cannot Drive 4-6 hours after dilation
* Sx of AACG and action required
* Dilation leaflet
What are the features, ocular side effects, cautions and characteristics of tropicamide?
- Available as: 0.5 & 1%
- Time to full mydriasis: 20 – 30 minutes
- Duration: 6-7 hours
- Typical dose: 2 x 0.5% (5 mins apart)
- POM
Ocular Side Effects of Tropicamide - Transient stinging
- Less severe than cyclopentolate & atropine
- Elevation of IOP of eyes with Chronic Open Angle Glaucoma
- Safest agent for use in mydriasis in children & adults
- Photophobia
Þ Ask the patient to bring sunglasses - Blurred Vision
Þ Patient should not drive or operate machinery whilst dilated
Cautions of Using Tropicamide - Myasthenia gravis
- Angle closure glaucoma
Characteristics of Tropicamide - Reported non-selective to muscarinic receptors
- Although may be selective to M4 receptors
- Mostly unionised at physiologic pH (absorbs better)
- Unionised molecules readily penetrate the corneal epithelium
- Faster diffusibility may account for faster onset & shorter duration than other
anticholinergics
What are the cautions/contraindications of ALL mydriatics?
- Allergies/Known hypersensitivity
- Known angle closure/narrow angles (hyperopes)
- Iris mounted IOLs
- Neonates – can’t metabolise the drug
- Diabetes: Causes a reduced effect of the drug
- Thyroid eye disease: The eyes become more sensitive
- Keratoconics: Urrets-Zavalia Syndrome
Describe the features of cyclopentolate?
– available in 0.5% & 1% and widely used cycloplegic drug – POM drug
o Cyclopentolate is an antimuscarinic (competitive antagonist for muscarinic receptions)
o <3 months not recommended, 3 months – 12 years – 1 drop of 1%, 12 years to adult – 1 drop of 0.5%
o Allow 40 mins before carrying out refraction (allow 0.5D for ciliary tonus reduce cyclo rx by 0.5D)
o Maximum cycloplegia achieved at about 40mins last up to 24 hours focusing returns within 6-12 hours
o Maximum Mydriasis achieved at about 20mins last up to 24/48 hours
o Adverse reactions rare – hypersensitivity may
What are the features, clinical uses, ocular effects, side effects and systemic side effects of phenylephrine?
- Available as 2.5% & 10%
- Time to full mydriasis: 45-60 minutes
- Duration: 6-7 hours
- Dose: 2 x 2.5% (5 minutes apart)
- POM or P
Clinical Uses of Phenylephrine - Fundus examination testing for oculosympathetic lesions (Horner’s)
- Ocular surgery (LASIK)
- Relief of minor allergic reactions
Ocular Effects of Phenylephrine - Causes mydriasis
- Increased Palpebral aperture
- Vasoconstriction
- Increased aqueous outflow
Ocular Side Effects of Phenylephrine - Transient pain (but not as stingy as tropicamide)
- Lacrimation
- Keratitis
- Pigmented aqueous floaters
- Rebound miosis
- Rebound conjunctival congestion
- Conjunctival hypoxia
Systemic Side Effects of Phenylephrine - Systemic hypertension
- Occipital headache
- Subarachnoid haemorrhage
- Ventricular arrythmia
- Tachycardia
- Reflex bradycardia
- Blanching of skin
What are the indications, contraindications, cautions, medications to avoid concordant use with and characteristics of phenylephrine?
Indications
* Typically used in combination with tropicamide where pupil dilation is not sufficient when
tropicamide is used alone
* Synergistic Combination – use of both anti muscarinic and sympathomimetic to achieve
maximum dilation (0.5% tropicamide and 2.5% phenylephrine)
* Pupil reactions are retained hence not great effect during optometric examination
* Very mild cycloplegic effect – not clinically significant
Contraindications
* Children & over 65 as increased risk of systemic toxicity
* Neonates
* Hyperthyroidism
Cautions
* Asthma
* Diabetes
* Stroke
Medications to avoid when giving Phenylephrine
* Adrenergic agonists
* Monoamide oxidase inhibitors
* Oxytocin
* Doxapram
* MAOIs
Characteristics of Phenylephrine
* It is a synthetic sympathomimetic amine
* Acts primarily on alpha receptors & has little/no effect on beta receptors
* Has a minor role in releasing norepinephrine from adrenergic nerve terminals
* Clear/colourless or slightly yellow
* Oxidises on exposure to light or heat
* Can be reversed with pilocarpine, but this can cause pupil block
What are the types of anaesthetic used?
- Tetracaine – Stings the most
- Lidocaine
- Oxybuprocaine
- Proxymetacaine – Stings the least
