Dilating drops (Mydriatics and Cycloplegics)

Dilating drops generally have the dual function of mydriasis and cycloplegia, the latter being caused by paralysis of the ciliary muscle and so paralysis of accommodation.¹ They are used both for the examination of the fundus (more short acting agents), for cycloplegic refraction and as part of the treatment regimen in the management of acute anterior uveitis where the pupil is kept dilated to prevent the formation of adhesions between the posterior aspect of the iris and the lens (posterior synechiae). The strength of the drug and its duration of action dictates the choice of drug. The age of the patient also guides choice.

• These drugs cause transient blurring of vision: check with the patient that this is not going to be a problem (e.g. if they are driving or need to carry out tasks requiring good visual acuity) and document that they have been advised of this. Patients should refrain from driving for 1-2 hours.
• Some patients do not experience any blurring of vision until they try to accommodate (e.g. try to read). They may therefore not notice any drop in visual acuity until they get home - warn them of this, as it can be quite alarming.
• Choose the shortest acting agent that is practically possible.
• Darkly pigmented irides are more resistant to pupillary dilation: initially give them more time rather than more drops as overdosage is possible.
• Mydriasis can precipitate acute angle closure glaucoma in a very small number of susceptible individuals (previous episode and high hypermetropia - very long sighted).

• Example - phenylephrine (2.5%, 10%)
• Use - short duration mydriasis
• Action - sympathomimetic amine with predominantly direct alpha-adrenergic action
• Contraindications - angle closure glaucoma, severe hypertension, hyperthyroidism, partial heart-block, myocarditis, bradycardia or serious impairment of the coronary circulation³
• Caution - children and elderly (avoid 10% strength). May interact with systemically administered monoamine oxidase inhibitors.
• Administration - stat dose (2.5%) for fundal assessment. 6-12 hourly (2.5%) for anterior uveitis. Higher strength used in the context of surgery.
• Ocular side-effects - transient stinging, blurred vision, photophobia
• Systemic side-effects - arrhythmia, hypertension, coronary artery spasm

• Examples - atropine sulphate, homatropine hydrochloride, cyclopentolate hydrochloride, tropicamide
• Use - mydriasis and cycloplegia of short, medium and long term duration
• Action - block the effect of acetylcholine at muscarinic receptor sites³
• Caution - infants less than 3 months: risk of systemic effects with drop application
• Administration - stat dose for fundal assessment. 6-12 hourly dose for anterior uveitis (as directed by specialist team)
• Ocular side-effects - transient stinging, blurred vision, raised intraocular pressure, contact dermatitis and reactive conjunctivitis
• Systemic side-effects - (rare in topical administration unless very young): dry mouth, dry skin, arrhythmias, urinary retention and constipation

Choice is guided by need but in a primary care setting, it is generally best to choose fast and short acting drops.