Pediatric Ophthalmology
Edited by P. F. Gallin
Thieme Medical Publishers, Inc.
New York ©2000

9

Ocular Pharmacology in Children

KIM L. COOPER, KULDEV SINGH, AND THOM J. ZIMMERMAN

Adult medications considered innocuous may be potentially hazardous in children, especially neonates. Cycloplegic, mydriatic, antiaccommodative, antibiotic, antiinflammatory, and intraocular pressure-lowering medications all are commonly used in children. This chapter will address therapeutic issues pertaining to the use of these agents in children.

Pharmacological Considerations Unique to Infants and Children

Drugs that have been approved by the Food and Drug Administration for use in adults but not children should be used with caution. There is perhaps greater responsibility and vulnerability when a physician prescribes a drug not approved for use in children based on his or her own judgment. We must weigh potential benefits and risks of the medications. For this reason as well as the relative inability of children to describe side effects the ophthalmologist should be particularly careful in looking for untoward signs and symptoms of toxicity.

Multiple organs and organ systems may be adversely affected by topical ocular medications.¹ These effects may be allergic or dose related. Neonates, especially when premature, may be particularly vulnerable to dose-related side effects. The ophthalmologist should work in conjunction with the neonatologist or pediatrician to jointly assess the risk of ocular medications.

All topical ocular medications have the potential to be absorbed systemically through the nasolacrimal system. There is considerable variability in the drug levels found systematically in patients.¹ Nasolacrimal occlusion may be effective but is often difficult in uncooperative children.

Dilation

Cycloplegic Agents

This class of drugs plays an important role in the diagnosis and therapy of eye disorders in infants. Ocular cycloplegic agents block muscarinic receptors in the ciliary body, thereby paralyzing the ciliary muscle and relaxing accommodation. Because the constrictor muscles of the iris also are blocked, which allows the iris dilators to act unopposed, dilation is often another secondary effect of cycloplegic therapy. The antimuscarinic effect of cycloplegic agents is dose dependent.¹

Cycloplegic agents are used routinely to relax accommodation when performing retinoscopy in children. Pupil dilation is often augmented by an additional mydriatic agent, which allows better visualization of the retina and optic nerve. Darker pigmented irides dilate more slowly2 and often require a second dose of medication.

Cycloplegic agents also are commonly used in inflammatory eye conditions. In addition to decreasing the potential risk of posterior synechiae, these agents may relieve ocular discomfort by diminishing ciliary body spasm.

The most commonly used cycloplegic agents in pediatric ophthalmology are tropicamide (Mydriacyl), cyclopentolate (Cyclogel), atropine, homatropine, and scopolamine.

Tropicamide (0.5 and 1.0%)

Tropicamide is a weak cycloplegic agent with rapid onset of action. Used alone, it is less reliable than cyclopentolate in relaxing accommodation for cycloplegic retinoscopy and refraction³ and therefore is most often used in conjunction with cyclopentolate. Despite this, it continues to be commonly used in routine eye exams both to partially relax accommodation and to dilate the pupil. It is a relatively safe cycloplegic agent without reported serious adverse systemic side effects.

Cyclopentolate 0.5, 1, and 2%

Cyclopentolate remains the cycloplegic agent of choice in most routine pediatric eye exams, especially when cycloplegic refraction is necessary. It can be used in conjunction with tropicamide. The peak accommodative effect occurs in approximately 20 to 45 minutes in most eyes. Residual accommodative effects and pupil dilation may last from 24 to 36 hours, most often reversing between 1 ½ and 3 hours.

Because of the possibility of severe dose-dependent systemic side effects with this agent, the use of 2% cyclopentolate has become obsolete. Although local or systemic allergic reactions to the drug may occur, they are rare.⁴ Feeding intolerance and gastrointestinal discomfort are relatively common side effects.⁵ Hyperthermia, hyperactivity, hallucinations, seizures, and delirium have also been described.⁶

Atropine (0.5 and 1.0%)

Atropine is the slowest in onset, longest acting, and likely the most completely paralyzing commercially available antiaccommodative agent. Because the duration of action is often 1 week or greater, atropine is rarely used for routine ophthalmic examinations unless complete or prolonged ciliary muscle paralysis is desired. It is often used in amblyopia therapy, following glaucoma procedures, and as a treatment adjunct for intraocular inflammation.

Ocular side effects of atropine include follicular conjunctivitis and contact dermatitis.⁷ Hypotension, hyperthermia, respiratory depression, delirium, and death also have been reported. Other physicians, including intensivists and anesthesiologists, should be informed of the use of these medications, especially when administered only in one eye. Parents should be instructed that, in the event of head trauma or car accidents, medical personnel should be informed of the use of ocular dilating agents to prevent any misdiagnosis of compressive intracranial nerve injuries.

Homatropine (2 and 5%)

Homatropine has a shorter onset and duration of action but is otherwise quite similar to atropine. It is a useful alternative to atropine in inflammatory eye conditions when mild pupillary mobility is desired. It should not be used in patients who are allergic to atropine.

Scopolamine (0.25%)

Scopolamine is a rarely used cycloplegic agent that has the benefit of not being cross-reactive with atropine and thus can be used in atropine allergic patients.⁶

Mydriatic Agents

Although cycloplegic agents may dilate the pupil, and thus may be considered mydriatic agents, the mydriatic agents discussed in this section primarily dilate the pupil without significant antiaccommodative action.

All mydriatic agents have sympathomimetic activity in that they mimic the action of epinephrine and norepinephrine by affecting α- or β-catecholamine receptors. Both α and β receptors have two subtypes, α-1 and -2 and β-1 and -2.¹

Phenylephrine hydrochloride (1.0, 2.5, and 10.0%) is a commonly used mydriatic agent that often is used in conjunction with a cycloplegic drug. It acts directly on catecholamine receptors with primarily α-1 activity. It has a rapid onset (less than 15 minutes) and a duration of action of approximately 6 hours. Although 10.0% phenylephrine is sometimes used prior to cataract surgery in adults, it is rarely used in children because of the potential for untoward cardiovascular and systemic side effects. Increased blood pressure and bradycardia are the most commonly encountered problems. The 1.0 and 2.5% concentrations are associated with fewer cardiovascular side effects and are thus the preferred dilating agents.

Other uses of phenylephrine hydrochloride include vasoconstriction of conjunctival blood vessels at the time of strabismus surgery and temporary blanching of blood vessels in eyes with allergic conjunctivitis6–8 and episcleritis.

Both epinephrine and its prodrug dipivefrin are sympathomimetic drugs that lower intraocular pressure and secondarily dilate the pupil.

Apraclonidine and brimonidine are α-selective sympathomimetic drugs that lower intraocular pressure by decreasing aqueous humor production at the ciliary body but are not routinely used as mydriatics. The efficacy and side effect profiles of these drugs have not been well established in children.

Cocaine is a powerful topical anesthetic agent that is rarely used in children. Potential side effects, including tachycardia, hypertension, seizures, and arrhythmias, limit its use in pediatric ophthalmology.

Hydroxyamphetamine is a sympathomimetic agent used only to differentiate pre- and postganglionic lesions producing Horner’s syndrome. In preganglionic lesions, hydroxyamphetamine induces the release of norepinephrine at the neuromuscular junction resulting in pupil dilation, whereas pupil dilation is not seen in postganglionic lesions.

Medical Antiaccommodative Therapy

Accommodative esotropia is one of the most common forms of acquired strabismus. Excessive hyperopia and a high accommodative convergence-accommodative ratio are both etiologic factors. Numerous reports and reviews have established miotics as adjuncts to the optical and surgical treatments for accommodative esotropia.^9,10

Miotics constrict the pupil and act directly on the ciliary muscle. Cholinesterase inhibitors act indirectly by facilitating neuromuscular transmission, whereas parasympathomimetic agents directly cause accommodative spasm.^11,12 Because miotics effectively reduce accommodative effort, less accommodative convergence occurs. Conditions for the development of fusional amplitudes are encouraged.

Longer acting drugs such as echothiophate iodide [phospholine iodide (PI)] and demecarium bromide (humorsol) have largely replaced the shorter acting physostigmine and pilocarpine. Initially, low percentages of PI (0.3%) are used before bedtime. The dose is titrated upward on follow-up exams.^13,14

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