7.2 Dilation & cycloplegia (agents, contraindications)

Dilation and Cycloplegia

Pupillary dilation (mydriasis) and cycloplegia (paralysis of accommodation) are among the most common technician-administered procedures. Dilation widens the pupil so the physician can examine the crystalline lens, vitreous, retina, and optic nerve. Cycloplegia relaxes the ciliary muscle so an accurate refraction can be obtained, especially in children and hyperopes whose accommodation masks their true refractive error.

Why cycloplegic refraction matters

Children have powerful accommodation that can hide latent hyperopia and produce inconsistent manifest refractions. By temporarily paralyzing the ciliary muscle, a cycloplegic agent reveals the eye's true, relaxed refractive state and is essential when evaluating accommodative esotropia, amblyopia, and pseudomyopia. This is why the physician often orders cyclopentolate or atropine for a pediatric exam rather than the shorter-acting tropicamide used for a routine adult dilated fundus check. The technician should understand that the choice of agent reflects both the depth of cycloplegia needed and how long the patient can tolerate blurred near vision afterward.

The agents

Two receptor mechanisms produce dilation. Sympathomimetics stimulate the iris dilator muscle; anticholinergics (parasympatholytics) block the iris sphincter and, for the stronger agents, the ciliary muscle.

• Tropicamide (0.5%, 1%) is a short-acting anticholinergic. It produces mydriasis with weak-to-moderate cycloplegia. Onset is 15-30 minutes and effects resolve in 4-8 hours, making it the workhorse for routine dilated fundus exams.
• Phenylephrine (2.5%, 10%) is a sympathomimetic that produces mydriasis with no cycloplegia. It is often combined with tropicamide for maximal dilation. The 10% concentration is avoided in infants, the elderly, and cardiovascular patients because it can raise blood pressure.
• Cyclopentolate (0.5%, 1%, 2%) is a stronger, longer anticholinergic used for cycloplegic refraction; onset is 30-60 minutes and duration up to 24 hours. It can cause transient CNS effects in children such as drowsiness and disorientation.
• Atropine (1%) is the strongest and longest cycloplegic, lasting one to two weeks. It is used for cycloplegic refraction in young children and to treat amblyopia and uveitis-related pain. Its long duration and systemic anticholinergic toxicity (dry mouth, flushing, tachycardia, fever) demand careful counseling.
• Homatropine and scopolamine are intermediate-duration alternatives.

Onset and duration at a glance

Contraindications and the angle-closure risk

The most important safety step before dilation is assessing the anterior chamber depth and drainage angle. Dilating a patient with a shallow anterior chamber or an occludable (narrow) angle can precipitate acute angle-closure glaucoma, an emergency in which the mid-dilated iris blocks aqueous outflow and IOP spikes. Before dilating, the technician should:

• Estimate anterior chamber depth using the Van Herick technique at the slit lamp or a penlight oblique-illumination (eclipse) test.
• Review history for prior angle-closure attacks, very shallow chambers, or an iris that appears bowed forward.
• Ask about a known allergy to the agent.

Other cautions include phenylephrine 10% in cardiovascular disease and infants; atropine and cyclopentolate in Down syndrome and in children prone to CNS effects; and any anticholinergic in a patient with a history of angle closure.

Reversal, consent, and driving precautions

There is no routine reversal agent that technicians administer; dilation is allowed to wear off. Historically dapiprazole was used to reverse mydriasis but is no longer marketed, and pilocarpine is not used casually because of its side effects.

Before instilling drops, obtain informed consent by explaining what dilation is, why it is needed, and its temporary effects: blurred near vision, difficulty reading, and light sensitivity (photophobia) lasting several hours, longer for cyclopentolate and days for atropine. Advise patients not to drive until vision returns to normal, and confirm they have sunglasses or a driver, because glare and blurred vision impair driving. Warn every patient, but especially those flagged with narrow angles, to seek immediate care if they develop severe eye pain, headache, nausea, halos around lights, or markedly blurred vision after dilation, as these are signs of angle closure. Documenting the drops given, concentrations, times, and the consent discussion completes the procedure and protects both patient and practice.

Instillation and pediatric considerations

For dilation the technician instills the drop into the inferior fornix, then applies punctal occlusion to limit systemic absorption; this is especially important with phenylephrine 10% and atropine, whose systemic effects can be significant in small children and frail adults. In infants and young children, a spray or diluted-strength combination is sometimes used to reduce the systemic dose, and the caregiver may gently restrain the child while the drop is placed in the medial canthus for the child to blink in. Always confirm the maximum pupil dilation before the physician's examination, and re-instill only per order if dilation is incomplete. Note the pre-dilation pupil size and reactivity in the chart, because the physician may need that baseline. If a patient reports a prior severe reaction to a dilating agent, flag it prominently. These precautions, combined with clear counseling on temporary blur and photophobia, make dilation a safe, routine, and well-tolerated procedure for nearly every patient.