| Chapter 41 Cycloplegic Refraction LEONARD APT and WILLIAM L. GAFFNEY Table Of Contents |
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INDICATIONS UNDESIRABLE EFFECTS CYCLOPLEGIC PROTOCOL CURRENT CYCLOPLEGIC AGENTS REFERENCES |
| INDICATIONS |
| The refracting power of the eye results from the static power of the eye (the combined ability of the cornea and the lens to bend incoming
rays of light) and the accommodative power of the eye (the variable force of accommodation that alters the path of
light rays by causing the ciliary body to change the curvature of the
lens). The total increase in plus power that accommodation produces
is known as the amplitude of accommodation. Cycloplegia inhibits the accommodative
power of the eye by blocking the action of the ciliary muscle, allowing
the static or objective refractive error of the eye to
be measured. The best way to obtain paralysis of accommodation is to use
cycloplegic drugs. Cycloplegic drugs are called anticholinergic because
they block the muscarinic action of acetylcholine. This action inhibits
cholinergic stimulation of the iris sphincter and ciliary muscle, which
results in mydriasis and cycloplegia. The younger the patient, the greater the patient's amplitude of accommodation and the more difficult it is to inhibit it. Because of the powerful accommodation and the inability of young pediatric patients to respond with accurate subjective responses, cycloplegic refraction rather than manifest or subjective refraction usually is necessary. In older children and adults, noncycloplegic methods of inhibiting accommodation, such as fogging, become more practical clinically, but cycloplegics can be used selectively to help determine the refractive state of the eye. |
| INDICATIONS |
| Cycloplegia is necessary for controlling accommodation and obtaining an
accurate refraction in young children. No other technique, such as fogging, can
replace cycloplegia for preciseness in determining refractive
errors in early childhood because it does not depend on patient cooperation
or fixation distance. Cycloplegic examinations not only allow refractive error to be determined, they also dilate the pupil, preparing the patient for an ophthalmoscopic examination. All children require a thorough ophthalmoscopic examination, which enables the physician to look for opacities in the ocular media and abnormalities in the inner eye. In older children and young adults, cycloplegic refraction can confirm the diagnosis of accommodative spasm, which is a constant or intermittent, involuntary increase in ciliary contraction. Ciliary spasm may be caused by spasm of the near reflex or high ciliary tonus, or secondary to factors such as hyperopia or convergence insufficiency.1 Patients with low hyperopia may present as myopic during examination; this so-called pseudomyopia can be identified by cycloplegic evaluation. Although indicated for all patients with ocular motility disorders, cycloplegic refraction is indispensable to the clinician in diagnosing and managing accommodative vergence anomalies. The role of accommodation in esotropia is well recognized. A fully accommodative deviation exists when no tropia is present after accommodation is fully relaxed. Most esotropic vergence disorders are partly accommodative and are characterized by an abnormal accommodative-convergence ratio. Treatment includes blocking accommodation by the use of plus lenses and miotics. The entire hypermetropic refractive error is usually prescribed in the spectacle correction of children with esotropia who are less than 5 years of age. Complete blockade of the ciliary hypertonus is necessary to eliminate all accommodation-induced convergence. If adjustment to the full hypermetropic correction is not prompt, a short course of a cycloplegic drug such as atropine is useful. The key to determining the full hypermetropic correction is a proper cycloplegic refraction, repeated one or two times several months apart. In most cases of esotropia with hypermetropia in children less than 5 years of age, atropine or scopolamine preferably is used to ensure that no residual accommodation goes unrecognized. Several investigators have shown atropine to be more effective than cyclopentolate in blocking accommodation in young esotropic children.2,3 The indications for cycloplegic refraction are limited in adults. As amplitude of accommodation gradually decreases with age, a closer agreement between cycloplegic and manifest refraction findings takes place. The 17 diopters of accommodation of a 3-year-old child decreases to 14 diopters at 10 years of age, 10 diopters at 25 years of age, 6 diopters at 40 years of age, and 2 diopters or less at age 50. Cycloplegia may be necessary in handicapped or mentally disabled individuals because of their unresponsiveness to subjective refraction; it also may be used to objectively evaluate the suspected malingerer or hysteric. Young adults with asthenopic symptoms who use their accommodation to compensate for their hyperopic refractive error may require a cycloplegic examination when the manifest refraction reveals too little hyperopia to account for their symptoms. Blurred vision or headaches after sustained reading or changing focus from near to far may be caused by latent hyperopia. With the advent of modern laser refractive surgery, cycloplegic refraction has become a valuable preoperative test for accurately determining refractive error. Cycloplegia can be used in pharmacologic occlusion therapy when the nonamblyopic eye is sufficiently hypermetropic that effective blurring of vision can be obtained by instilling a cycloplegic drug in that eye alone. The success of this penalization therapy can be determined in the office by blurring the sound eye with a short-acting cycloplegic agent, removing the spectacle correction, and evaluating the fixation preference. If under test conditions the patient switches from using the good eye to using the amblyopic eye, chances are excellent that he or she will also do so during treatment and that penalization will force the amblyopic eye to be used. Table 1 summarizes the indications for cycloplegic refraction.
TABLE 1. Indications for Cycloplegic Refraction Accurate refraction in young children
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| UNDESIRABLE EFFECTS |
| Because it is so difficult to fully suppress ciliary body function, cycloplegic
findings are not always consistent or complete. Retinoscopy findings
are more uncertain because of the ocular aberrations caused by
the wide mydriasis that accompanies cycloplegia. Repeated refractions
often are necessary to achieve accurate results. Cycloplegic refraction after childhood may require a post-cycloplegic manifest refraction in those children found to have significant hypermetropia. Eyeglasses cannot be prescribed based on cycloplegic findings alone because visual acuity may be reduced when the eye returns to its normal state of accommodative tonus. In those patients without a motility problem, the amount of reduction in plus lens correction is determined by the difference in manifest and cycloplegic refractions and the age and visual demands of the child. A cycloplegic refraction is inconvenient because the loss of accommodation and mydriasis may last several hours to several days after the examination. Pilocarpine does not effectively reverse the cycloplegia or mydriasis produced by anticholinergic cycloplegic drugs such as atropine and cyclopentolate.4,5 For these reasons, and because the resultant miosis and ciliary spasm can cause significant discomfort, the use of miotics to counteract anticholinergic drops is no longer advised. All cycloplegic drugs have potentially serious systemic side effects, especially in infants and children. Both allergic and toxic reactions may occur with their use. Specific adverse effects are included in the comments section for each individual cycloplegic drug described later in this chapter. Several references in the literature detail these side effects.4,6–13 Proper techniques of drug instillation can greatly reduce the hazards of cycloplegics. One drop of each drug is sufficient, if instilled directly into the eye, because the eye normally holds only about one fifth of 1 drop. Overflow onto the skin should be blotted away quickly; gentle eyelid closure for several minutes after drug instillation should be attempted. Digital pressure should be applied at the periphery of the nasolacrimal system at the medial canthus for several minutes, if possible. A second set of drops may be indicated 5 minutes or so later in darkly pigmented irides. The lowest dose necessary to produce adequate cycloplegia should always be used. Cycloplegic drugs can precipitate an attack of acute angle closure glaucoma in predisposed patients. A slight transient rise in intraocular pressure of little clinical significance may occur in glaucoma patients with open angles. Patients with open-angle glaucoma receiving miotics, however, may experience a distinct rise in intraocular pressure after the instillation of a cycloplegic drug when the miotic effect is counteracted. Table 2 lists the undesirable effects of cycloplegic refraction.
TABLE 2. Undesirable Effects of Cycloplegic Refraction Findings can be inconsistent and incomplete.
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| CYCLOPLEGIC PROTOCOL | ||||||||||
| Based on the authors' review of the literature and clinical experience, Table 3 was developed to guide other clinicians in the proper selection of cycloplegic
agents for different age groups. Tropicamide 0.5% can be used
in infants up to 3 months of age, and 1% may be used thereafter to enhance
the cycloplegic effect when cyclopentolate is used.14 A topical anesthetic (0.5% proparacaine) may be instilled initially to
improve the absorption and effectiveness of the cycloplegic drop and
to avoid the stinging sensation caused by subsequent drops.15,16 Phenylephrine drops can be added to enhance mydriasis for ophthalmoscopy.
TABLE 3. Choice of Cycloplegic Agent for Infants and Children
*Not commercially available. See atropine sulfate section.
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| CURRENT CYCLOPLEGIC AGENTS |
ATROPINE SULFATE PREPARATIONS. Solution, 0.5%, 1%, and 2%; ointment, 1%; atropine in oil, 0.25% (not commercially available).* One of the authors (L.A.) prefers to use 0.25% atropine in sesame oil for infants. This drug is specially prepared at the UCLA Medical Center Pharmacy. This preparation is comparable in action to 1% aqueous solution (unpublished data). Less toxicity has been encountered with its use because of the lower concentration of available drug; the chance of systemic absorption is smaller because the base of the drug is an oil rather than water. DOSAGE FOR CYCLOPLEGIA. One drop of 0.25%, 0.5%, or 1% solution 2 or 3 times daily for 1 to 3 days before examination and in the morning of the examination. The ointment form (preferred in infants; 1/8-inch strip of ointment) should be used twice a day for 1 to 3 days before examination. ONSET AND DURATION OF ACTION. Full mydriasis occurs in about 30 minutes; cycloplegia occurs in 60 to 180 minutes. Maximal cycloplegia is reached within 36 hours (usually after the fourth dose) and lasts up to 1 to 2 weeks. The cycloplegic effect is more profound when more than one drop is instilled. Atropine is less effective in eyes with darkly pigmented irides. CONTRAINDICATIONS. Atropine is best avoided in lightly pigmented children, children with Down syndrome, or brain-damaged infants because of a possible increased sensitivity to the drug.6 The drug should not be used in patients with angle closure glaucoma or patients with a tendency toward increased intraocular pressure because of a narrowed iris angle. COMMENT. Systemic toxicity, which can lead to death, may occur from an idiosyncratic response after the instillation of only 1 or 2 drops in each eye or from overdosage after multiple instillations of the drug. Parents must be advised of the early signs of toxicity (fever, skin rash, rapid and irregular pulse, dry mouth and nose, and delirium) so that administration of atropine is not continued. Table 4 contains instructions that can be given to parents for use at home. In the event of systemic atropine toxicity, prompt treatment with physostigmine salicylate (Antilirium) reverses both central and peripheral anticholinergic effects. The dosage of physostigmine salicylate is 0.02 to 0.03 mg/kg up to 2 mg IV, IM, or SC; the dose is repeated in 30 minutes and then every 1 to 2 hours as needed. Generally, atropine should be reserved for esotropic children less than 5 years of age. Its potential for toxicity in infants and children make its use undesirable unless esotropia is present or cycloplegia is inadequate with other drugs.
TABLE 4. Traditional Instructions for Cycloplegic Refraction*
*The traditional dosage regimen of atropine solution instilled three times daily for 3 days before examination is usually not necessary to obtain maximum cycloplegia. Furthermore, the 3-day dosage routine may lead to toxicity in young pediatric patients. Maximum cycloplegia usually is reached within 36 hours after four divided doses of atropine have been given. Therefore, a more practical dosage regimen is 1 drop of atropine solution three times on the day before and once on the morning of the examination.
HOMATROPINE HYDROBROMIDE PREPARATIONS. Solution, 2% and 5%. DOSAGE FOR CYCLOPLEGIA. One drop of 2% solution in each eye, repeated once in 5 to 10 minutes. ONSET AND DURATION OF ACTION. Onset of cycloplegia occurs in 10 to 30 minutes, with peak cycloplegia occurring in 30 to 60 minutes. Cycloplegia lasts 1 to 3 days. CONTRAINDICATIONS. Similar to those for atropine. COMMENT. Homatropine is a weaker cycloplegic agent than either atropine or scopolamine. The drug is infrequently used because its cycloplegic action is less complete than that of atropine and lasts longer than that of cyclopentolate, which is at least as effective. Systemic toxic reactions are similar to those from atropine. Physostigmine salicylate reverses the systemic toxicity of homatropine (see the dosage recommended in the comment on atropine). SCOPOLAMINE HYDROBROMIDE PREPARATION. Solution, 0.25%. DOSAGE FOR CYCLOPLEGIA. Although one drop in each eye twice daily for 2 days before refraction is often prescribed, we prefer one drop in each eye the night before and 1 hour before examination. ONSET AND DURATION OF ACTION. Maximal cycloplegia occurs within 1 hour and lasts 3 to 7 days. CONTRAINDICATIONS. Similar to those for atropine. COMMENT. The cycloplegic strength of 0.25% scopolamine hydrobromide and 1% atropine sulfate solutions are similar, and therefore, scopolamine can be substituted when atropine allergy occurs or when contraindications to atropine are present. Central nervous system (CNS) toxicity perhaps is more common from scopolamine. The systemic signs and symptoms of scopolamine toxicity are the same as those for atropine. Systemic toxicity is treated with physostigmine salicylate (see the dosage recommended in the comment on atropine). CYCLOPENTOLATE HYDROCHLORIDE (CYCLOGYL) PREPARATIONS. Solution, 0.5%, 1%, and 2%. DOSAGE. One drop of 0.5% solution in small infants. In other children or darkly pigmented infants, 1 drop of 0.5% or 1% solution, followed in 5 to 10 minutes by a second drop. The drug causes a marked transient stinging sensation after instillation, which can be minimized if preceded with a drop of proparacaine. ONSET AND DURATION OF ACTION. Onset of cycloplegia occurs in 15 minutes, with maximum cycloplegia reached in 30 to 75 minutes. Because the period of maximum cycloplegia is brief, refraction must be performed within 1 hour after instillation of the drug. However, to be certain that refraction is performed at the time of maximum cycloplegia, one must test for residual accommodation (at least 2 diopters or less). CONTRAINDICATIONS. The 2% concentration should be avoided, especially in newborns and young infants, to prevent toxicity. If a darkly pigmented patient exhibits resistance to cyclopentolate, it is better to use another cycloplegic such as atropine or scopolamine than it is to instill the 2% concentration several times. Premature and small infants are particularly susceptible to CNS, cardiopulmonary, and gastrointestinal toxicity from all concentrations of cyclopentolate.17 As with atropine, systemic toxicity is seen more often in patients with brain damage, a history of seizures, Down syndrome, or light pigmentation. COMMENT. Cyclomydril is a commercially available combination of 0.2% cyclopentolate and 1% phenylephrine. Although the concentration of cyclopentolate in Cyclomydril is low, the drug has been used by some workers as an adequate cycloplegic agent in preterm infants and newborns because although some accommodation function is present, it is not consistently or fully used. After the age of 3 months, 0.5% or 1% cyclopentolate is used. Systemic toxicity induced by cyclopentolate eyedrops is similar to that produced by atropine except that visual and tactile hallucinations are a more striking feature. Toxic reactions are dose-dependent and more likely to occur with the 2% solution. Even multiple applications of the 1% concentration may cause adverse reactions, such as drowsiness, hyperexcitability, disorientation, incoherent speech, hallucinations, ataxia, and seizures. Adverse systemic reactions have rarely been seen with use of the 0.5% concentration in children. The treatment of systemic cyclopentolate poisoning is the same as for atropine poisoning (see the discussion of treatment in the comment on atropine). TROPICAMIDE (MYDRIACYL) PREPARATION. Solution, 0.5% and 1%. DOSAGE FOR CYCLOPLEGIA. One drop in each eye; repeat once in 5 minutes. ONSET AND DURATION OF ACTION. Minimal and transient cycloplegic action in infants and children make this drug useful only as a mydriatic. Maximal cycloplegia occurs within 20 to 35 minutes after instillation, with a duration of only 10 to 40 minutes. Cycloplegic refraction therefore must be performed within a short time frame. CONTRAINDICATIONS. Tropicamide is a safe drug; CNS disturbances are rarely encountered. The drug may be used safely at any age as a mydriatic agent. COMMENT. Tropicamide combined with phenylephrine (2.5%) eyedrops produces wide pupillary dilation for ophthalmoscopy in all ages, and in darkly pigmented as well as blue irides. Tropicamide may enhance the cycloplegic effect of cyclopentolate.14 It generally is not effective as a sole cycloplegic agent in patients less than 40 years of age. Dapiprazole (Rev-Eyes) helps to reverse the decreased amplitude of accommodation produced by tropicamide.18 |