Week 1.08 Mydriatic Drugs Flashcards
What is the purpose of a mydriatic
Optometric - better view of fundus - small pupil, central cataract or corneal opacity
Ophthalmological - theraputic benefit - anterior uveitis, breaking of posterior synechiae
What is posterior synechiae
adhesions between posterior surface of iris and anterior surface of crystalline lens
What are the methods of mydriasis
- Blocking the parasympathetic branch of the ANS
(Stopping pupil constrict)
- blocking muscarinic receptors (anti muscarinic)
- unopposed action of dilator muscle causes pupil to increase - Stimulate sympathetic systenm (sympathomimetic drugs)
- Combination of anti muscarinic and sympathomimetic action - using two drugs on the same eye - provides maximal mydriasis
Indications for mydriasis
Worrying symptoms - flash float
Px at risk of ocular disease - RD high myope, diabetes
Doubt cause of ocular dysfunction - unexpected reduction in VA or VF
Difficult to get view - lens opacity, small pupil
Stereoscopic view on fundus
Contraindications of mydriasis
- Prev allergic response - new drug that interacts with mydriatic
- Iris fixated IOL - tucked in behind after cataract
- Cautions needed in narrow angle - angle closure glaucoma but might miss RD so weigh up the risks
What is the 4D drug test
Drug, dose, date, disposal
What should you do before dilating px
Previous allergic response
4D test - batch no
Check for other contraindications
Measure openness of anterior chamber angle
Check IOP before and after
Check pupil responses
Discuss tasks px should avoid until effects of drug have worn off
Risks
Explain what to the px?
- why
- effects
- how long effects for
- side effects
- drive?
- adverse reaction what to do
Post dilation checks
BEFORE PX LEAVES PRACTICE
- measure iop
- measure VA
- measure van herick
- leaflet
- adverse reaction what to do
A post dilation of what mmHg causes suspicion
Greater than 5mmHG
Especially unilateral rise in IOP
When is the greatest risk of COAG when dilation
Greatest risk is when gap between iris and lens is smallest – usually when the pupil is mid-dilated
Most likely to occur during the recovery period (i.e when the drug is wearing off)
So greatest risk of angle closure occurs several hours after dilation
Mydriatics available to optoms
Tropicamide (POM)
- 0.5% and 1%
- minim
- multidose e.g. mydriacyl 1%
Phenylephrine hydrochloride (P)
2.5% and 10%
Tropicamide
- anti muscarinic - antagonist for muscarinic receptors
- blocks acetylcholine binding so prevents pupil constricting
- relaxed sphincter and unopposed dilator muscle brings about dilation
Has some cylcoplegic effect
Rapid onset
15-20mins
Recovery 6-8hrs
What conc of tropicamide do we usually use
0.5%
When would be use 1.0% conc tropicamide
Px with high level of pigmentation
BUT not the enhanced cycloplegic effect in young px
What are the side effects of tropicamide
Ocular: photophobia, eye redness, irritation, blurred vision
Systemic: dizziness, headache, dry mouth
Cyclopentolate
Potent anti muscarinic agent
Induces long lasting mydriasis
Significant cylcoplegia
Not a drug of choice for mydriasis - too powerful
Phenylephrine
- sympathomimetic
- dilates pupil by stimulating radial muscles
- acts directly on alpha 1 adrenoreceptor
- amplitude of accomodation decrease in young px by ~2D
Also widens palpebral aperture due to stimulation of mullers muscle
Blanching of conjunctiva
What is the inset and recovery for phenylephrine
Onset ~1hr
Recovery 3-4 hrs
Sector dilation
- Partial dilation of the pupil by application of phenylephrine to a sector of the iris
- Useful in px at risk of angle closure
Phenylephrine side effects
Ocular side effects:
- irritation, blurred vision, photophobia
- Conjunctival allergic reaction, punctuate keratitis
Systemic side effects:
- Palpitations, tachycardia, arrhythmias, hypertension, headaches
What are synergistic combinations
Antimuscarinic + sympathomimetic
Relaxation of the sphincter muscle + contraction of dilator muscle
Tropicamide and phenylephrine
- achieves widely dilated pupil
- can use a lower concentration of drug
