Mydriatics Flashcards
why would you use a mydriatic?
- enables a more thorough examination of the eye eg peripheral crystalline lens, vitreous, fundus
- facilitates a stereo fundus exam
- for treatment eg uveitis - stops iris sticking to the lens, preventing an increase in IOP
when would you use a mydriatic?
1) px at risk of ret detachment - high myopia (>5D), family, trauma
2) Symptoms - unexplained vision loss/ VF loss/ disturbance or floaters, flashes, veils, shadows
3) Screening - diabetics, hig myopia, prior to ocular surgery
4) Inadequate fundus view - lens/media opacities, miotic pupils (less than 2mm)
what to do prior to dilation
- good reason to use the drug
- explain procedure
- px consent
- issue written information
- adverse effects - glare, loss of stereo vision, driving, operating machinery
- minimise risk of adverse reaction
- check for contraindications
how to instil and what to record
having explained the procedure and obtained th epx consent
- ask the px to look up
- pull down lower lid
- instil one drop into lower conjunctival sac
- occlude puncta - avoids drug draining into the nasolacrimal duct thereby reducing the effectiveness of the drug in the eye and increasing th elikelihood of causing systemic signs and symptoms
- record drug, strengt, dosage, exp date, batch no, and time of instillation
general contraindication of mydriatics
- known hypersensitivity to the drug
- iris clip IOLS - not common
- narrow angles - check for vh
- px with symptoms suggestive of sub acute or chronic closed angle glauc
- px with diagnosed CAG
- px using pilocaarpine for glauc treatment (constricts pupil which opens up drainage channels) - wouldnt want to use it in these pxs
symptoms of closed angle glacoma
- blurred vision
-halos - headache
- painful
- vomiting/nausea
- photophobia
- closed angle
- fixed mid dilated pupil
- cloudy cornea
- conjunctival hyperaemia
- sudden increae in IOP (usually >40mmHg)
how to minimise risk of CAG
1) IOP - take pre and post dilation
- significant rise in IOP/ asymmetric rise
- monitor rise in IOP
- refer to eye casualty if continues to rise
2) Check anterior angles
- gonioscopy, van herrick, others
3) Existing symptoms
- ask if already has signs of angle closure eg halos around light, painful eye
4) Use of miotic drug
- not generally used in optometric practise
5) Any allergies to the drug/ previous reactions?
van herricks technique
- used to estimate ant chamber depth
- microscope normal to corneal apex
- illumination at 60 degrees to microscope
- narrow slit beam 1mm
- low mag (16x)
- compare width of ant chamber to width of corneal section
muscarinic antagonists/ antimuscarinic/ anticholinergic
tropicamide - most commonly used
cyclopentolate - rarely used as a mydriatic
atropine - only available to independent prescribers, unlikely to be used as mydriatic
name a drug that is a sympathomimetic/ alpha agonist
phenylepherine - used more in USA
ANS (parasympathetic)
Transmitter = acetylcholine
receptor = muscarinic
muscles = ciliary and sphincter
ANS (sympathetic)
transmitter = noradrenaline
receptor = alpha
muscle = dilator
inducing mydriasis
inner circular muscle = iris sphincter muscle = pupilary constrictor
- parasympathetic stimulation causes contraction of the iris sphincter muscle and constriction of the pupil - blocking Ach causes dilation = tropicamide
outer radial muscle = iris dilator muscle = pupilary dilator
- sympathetic stimulation of the adrenergic receptors causes the contraction (shortening) of the iris dilator muscle and subsequently dilation of the pupil - pretends to act as noradrenaline = phenylephrine
antimuscarinic action
- iris sphincter muscle is controlled by parasympathetic innervation
- paralysis of parasympatheitc nervous system inhibits the action of Ach
produces: mydriasis, cycloplegia, reduced tear secretion - px may complain eye feels dry after instillation
sympathomimetic action
- noradrenaline is the transmitter in the sympathetic system
- neurohumoral transmitter at most sympathetic postganglionic neuro effector junctions
exceptions - sweat glands and vasodilator fibres on skeletal muscle
alpha and beta receptors
- mainly alpha 1 receptors in dilator pupillae muscles
- aplha 1 excitatory, alpha 2 inhibitory
- beta 1 excitatory, beta 2 inhibitory
tropicamide duration
mydriasis - 15 mins
recovery - 8-9 hrs
light reflex absent
induces a mild cycloplegic effect
may cause rise in IOP but likely to be transitory
few contraindications
tropicamide availability
- pom for use and supply by all optoms
- single use - 0.5% and 1% tropicamide HCL minims (B&L), store below 25 degrees
- multi dose containers, again 0.5 and 1% (alcon), store 2-8 degrees, protect from light
- 1% sometimes used for darker irides but will also lead to an increased cycloplegic effect
- pregnancy - avoid if poss, but better than using phenylephrine
- women who are using tropicamide must not breast feed
tropicamide side effects
ocular:
- transient stinging
- transient blurring
- photophobia
-raised IOP
- prolonged administration may lead to irritation, hyperaemia, oedema, conjunctivits
general body:
- CNS effects - dry mouth, reprted in children (blue eyes and blond hair)
phenylephrine availabilty and its possible effects
- p medicine
- single use minims (B&L) - 2.5% and 10% phenylephrine HCL, store at 25 degrees, protect from light
- 10% is contraindicated in children and elderly (>65 yrs) because of the increased risk of systemic toxicity
- less effective on highly pigmented eyes
- may cause widening of palpebral aperture
- blanching of the conjuncitva - vasoconstriction of conj blood vessels
phenylephrine contraindications
- medication - cv problems eg anti hypertensives, tachycardia
- medication - depression eg monoamine oxidase inhibitors, tricyclic antidepressants
- thyrotoxicosis
- insulin dependent diabetes
- asthma
- pregnancy/ lactation - may cause transient fetal hypoxia
- use of pilocarpine - older px = pupil block, young px = accommodative spasm
side effects of phenylephrine
ocular
- transient stinging
- transient blurring
- photophobia
- lid retraction
- conjunctival allergic reaction
- punctate keratitis
general body
- palpitations
- tachycardia
- cardiac arrhythmias
- htn
- h/as
drug gains access to systemic blood supply
synergistic combinations
- use of two or more substances to provide an effect greater than the sum of their separate effects
- combinations of antimuscarinic and sympathomimetics can be considered (eg tropicamide 0.5 and phenylephrine 2.5)
- allows lower conc of antimuscarinic to be used = less cyclo effect
mydriasert
-pom
- insoluble opthalmic insert
- contains phenylephrine and tropicamide
- gradual release
- used pre operatively and diagnostically
- in adults - insert up to max 2 hrs before procedure, remove within 30 mins of mydriasis and within 2 hrs of application
other mydriatic drugs
cyclopentolate ( antimuscarinic) - used to be available in 0.1%, cycloplegic ffects
homatropine (anti muscarinic)
- mydriatic effect commences in 10-20 mins
- maximal mydriasis 30-40 mins
- both light and accommodative reflexes absent
- recovery can take up to 3 days
