Ординатура / Офтальмология / Английские материалы / Clinical Ocular Pharmacology 5th edition_Bartlett, Jaanus_2008

An understanding of the mechanics of pupillary dilation lends support to the various philosophies governing the dilation of eyes with narrow angles.

Mechanics of Pupillary Dilation and Angle Closure

Eyes with deep anterior chambers are essentially free of the risk of pupillary block and iris bombé. However, in eyes predisposed to angle-closure glaucoma, the lens is generally displaced anteriorly, which increases the pressure of the iris against the lens.This situation favors pupillary block and iris bombé with subsequent secondary angle closure.

When the iris rests on an anteriorly positioned lens, the forces of pupillary dilation (iris dilator muscle activity) can be resolved into two components: posterior and lateral. Likewise, the force of pupillary constriction (iris sphincter muscle activity) can be resolved into two components: medial and posterior (Figure 20-6A). The total sphincter pupillary blocking force varies according to size and position of the pupil. A miotic pupil is generally associated with a taut iris and small pupillary blocking force, a mid-dilated pupil is associated with a lax iris and large pupillary blocking force, and wide dilation is associated with a compressed iris and small pupillary blocking force. Thus, the position of greatest risk with respect to potential angle closure is mid-dilation. With a mid-dilated pupil, regardless of how it is obtained pharmacologically, the pupillary blocking force is maximum, and if predisposed to angle closure, some eyes undergo acute angle closure because the pupillary block has increased the pressure in the posterior chamber. The increased pressure in the posterior chamber produces iris bombé, which presses the iris against the cornea, blocking aqueous access to the drainage angle, and leads to secondary angle closure (Figure 20-7).

Narrow Angle After Surgical

Iridectomy or Laser Iridotomy

Peripheral iridectomy or iridotomy removes the risk of pupillary block by creating a channel between the

posterior and anterior chambers, reducing pressure in the posterior chamber and thus preventing iris bombé. Thus precipitation of angle closure must be primary rather than secondary to pupillary block and iris bombé, providing the peripheral iridectomy or iridotomy is patent. Eyes with plateau iris undergo angle closure by a mechanism involving crowding of the iris against the trabecular meshwork rather than by a mechanism involving pupillary block.Although it is possible to induce angle closure with mydriatics despite a patient iridotomy in a patient with plateau iris syndrome, it is extremely rare.Therefore once it is established that the peripheral iridectomy or iridotomy is indeed patent, the routine drug regimen may be used to dilate the patient’s pupils.

Routine Dilation of Narrow Angle Patients

A valid approach to the dilation of eyes with extremely narrow angles is to refer the patient for a peripheral iridotomy before dilation. However, if dilation must be performed, then use of routine drug regimens, such as a combination of tropicamide and phenylephrine, is recommended to avoid a mid-dilated state. If drug-induced angle closure occurs and is promptly recognized and treated, the patient ultimately benefits from the experience, because the angle-closure attack occurs under controlled conditions in which proper treatment is readily available.

Pupillary block

Angle closure secondary to iris bombé

Figure 20-7 Pupillary block causes increased pressure in the posterior chamber relative to the anterior chamber. This produces iris bombé, which obstructs aqueous outflow and causes secondary angle closure.

However, before proceeding with such an approach, the practitioner should obtain the patient’s informed consent (see Chapter 5), dilate only one eye at the initial visit, and postpone dilation of the fellow eye until the response of the initial dilation has been ascertained. Because most angle-closure attacks occur 4 to 8 hours after instillation of the mydriatics, the dilation should be performed earlier in the day, when appropriate emergency care is more readily available. If angle closure occurs, the IOP usually is brought readily to normal levels because angle closure after dilation is rarely complete. Before the patient is dismissed the angle should be evaluated, the IOP should be determined, and the patient should be informed of the symptoms of acute angle-closure glaucoma and be given specific instructions for emergency treatment should it become necessary. The use of cholinergic miotics after dilation is discouraged, because it is both unnecessary and may actually induce angle closure by increasing pupil block.

Sector Dilation

An alternative to full dilation of the pupil is sector dilation, first described in 1967. This procedure primarily dilates the inferior aspect of the pupil. A small, pearshaped, partially dilated pupil can be obtained by placing a cotton pledget moistened with 2.5% phenylephrine in the inferior conjunctival sac. The pledget should remain for only 2 to 3 minutes, because too much drug delivery can cause complete dilation of the pupil. Tropicamide cannot be used for sector dilation because it paralyzes the iris sphincter muscle, allowing the entire pupil to dilate, whereas phenylephrine causes the dilator to contract, pulling open just a sector of the pupil. A vertically oval pupil results (Figure 20-8). Alternatively, the tip of a thin strip of filter paper (Schirmer’s strip) can be moistened with 2.5% phenylephrine and placed in the inferior conjunctival sac. The paper should remain for only 1 minute, because longer contact may dilate the entire pupil. Another technique is applying a sterile cotton-tipped

Figure 20-8 Vertically oval pupil produced by sector dilation.

Figure 20-9 Sector dilation technique using cotton-tipped applicator held at inferior limbus. Phenylephrine-moistened swab is applied for approximately 20 seconds.

applicator moistened with 2.5% phenylephrine for approximately 20 seconds to the inferior limbus of the anesthetized eye (Figure 20-9).

Before sector dilation the eye should be anesthetized topically to reduce subsequent lacrimation, which might dilute and spread the mydriatic. The sectorially enlarged pupil, obtained from sector dilation, usually allows easy access to the posterior pole of the eye by enabling satisfactory binocular indirect ophthalmoscopy or other procedures requiring stereopsis. Although this technique may not necessarily prevent angle closure, it does seem to reduce the risk of angle closure because of the minimal and brief focal dilation.

Dilation After Cataract Surgery

Patients who have had cataract extraction with implantation of an intraocular lens (IOL) often have pupils that dilate less well than they did preoperatively. The poorer pupillary response probably relates to the amount of iris trauma occurring at surgery. The difference in mydriatic response may affect evaluating and treating peripheral retinal abnormalities in aphakic and pseudophakic eyes. However, even with maximally dilated pupils often the capsulotomy is the limiting factor.

Wide dilation is possible in pseudophakic eyes in which an anterior or posterior chamber lens has been implanted (Figure 20-10). Dilation can be safely accomplished even if the IOL appears to be slightly malpositioned. Dilation of the pupil does not change the position of these IOLs, unlike that of an iris-fixated IOL, which cannot be dilated without dislodging the IOL.

Figure 20-10 Wide pupillary dilation of eye with posterior chamber intraocular lens.Arrows denote edge of lens.

Although rare, an important complication of mydriasis in pseudophakia is pupillary capture. Here, the IOL becomes entrapped within the pupillary aperture and the pupil cannot return to its normal size after dilation (Figure 20-11). Several conditions can predispose the eye to pupillary capture, including damage to the crystalline lens zonules or to the capsular bag during surgery, IOL fixation into the ciliary sulcus, and the presence of nonangulated IOL haptics.

If pupillary capture persists, secondary complications can occur, including pupillary block glaucoma, iris chafing, iris sphincter erosion, and disruption of the blood–aqueous barrier with secondary inflammation

Figure 20-11 Posterior chamber intraocular lens entrapped within the pupillary aperture after dilation. (Courtesy Hernan Benavides, O.D.)

Figure 20-12 Plateau iris. Dilation of the pupil causes the iris to obstruct aqueous outflow, thus causing acute angle-closure glaucoma.

leading to corneal decompensation, cystoid macular edema, or hemorrhage. Because pupillary capture rarely leads to vision loss, noninvasive corrective procedures should be used initially to reposition the IOL; pupillary dilation and patient positioning alone may correct the problem. New IOL designs minimize these risks.

Plateau Iris

In 1960 the concept of plateau iris was first proposed and described. Although the prevalence of plateau iris configuration is unknown, it is believed to be quite rare.

Plateau iris configuration can result in angle closure by a mechanism independent of pupillary block. Because the anterior chamber has normal depth and the iris plane is flat, little or no pupillary block occurs. Instead, dilation of the pupil causes a peripheral iris roll to approximate and close the angle, thus precipitating an attack of acute angle-closure glaucoma (Figure 20-12). In eyes with plateau iris syndrome, ultrasonographic biomicroscopy demonstrates anteriorly positioned ciliary processes. These processes provide structural support beneath the peripheral iris, thus preventing the iris root from falling away from the trabecular meshwork after iridectomy or iridotomy. In most cases the diagnosis is made only after an apparently open angle has sustained angle closure after pupillary dilation. Once the diagnosis is established, the practitioner should exercise caution with future dilation.These eyes can sometimes be managed with peripheral laser iridoplasty.

POSTDILATION PROCEDURES

The routine measurement of IOP after dilation of the pupil is probably unnecessary. In nonglaucomatous patients with open angles, dilation with adrenergic mydriatics, such as phenylephrine, would not be expected to elevate the IOP, whereas dilation with relatively weak anticholinergic agents, such as tropicamide, would be

expected to slightly elevate the IOP in approximately 2% of patients. Thus patients with open angles can be dismissed after dilation, without regard to the IOP.

In contrast, monitoring the IOP after dilation of eyes with narrow angles is reasonable and prudent.The patient should be advised of the symptoms of angle closure and instructed to return to or telephone the practitioner’s office in the event of such an attack.

Use of Miotics

The instillation of pilocarpine to counteract the effects of the mydriatic is contraindicated. When pilocarpine is used after dilation with a regimen that includes phenylephrine, the relative pupillary block is likely to increase due to stimulation of the iris sphincter. In addition, pilocarpine increases aqueous outflow through the trabecular meshwork, which, in the presence of pupillary block, might create a greater differential pressure between the anterior and posterior chambers and lead to iris bombé with secondary angle closure. Pilocarpine can also reduce the depth of the anterior chamber, which exacerbates the factors causing angle closure. These changes may predispose the eye to angle closure, even in eyes in which closure seems unlikely.

The use of α-adrenergic antagonists is an effective and safe alternative to cholinergic miotics. Dapiprazole 0.5% (Rev-Eyes) can reverse mydriasis induced by 2.5% phenylephrine or 0.5% to 1.0% tropicamide. Unlike miosis induced by pilocarpine, the α-receptor blockade produced by dapiprazole does not shift the lens–iris diaphragm forward; the anterior chamber depth remains constant, and accommodation is not stimulated.The most significant side effects of dapiprazole are transient stinging or burning on instillation and conjunctival hyperemia lasting several hours in many patients.

COMPLICATIONS

Blurred Vision

Patients generally encounter some degree of blurred vision after dilation because of glare induced by light, spherical aberration associated with the large pupillary aperture, and accommodative paresis after use of an anticholinergic agent. In the latter instance, patients likely to encounter blurred distance vision are limited to those with uncorrected hyperopia. In addition, patients who have had photorefractive keratectomy may have greater coma-like and spherical aberration after pupillary dilation.

Most other patients should not encounter significant difficulty with distance vision associated with pupillary dilation. However, it is prudent to caution all patients who will be driving that poorer performance could ensue until the pupils return to normal size.

For reading and other near visual activities after dilation, myopic patients can remove their spectacles and

presbyopic patients can wear their reading lenses. Thus, with proper instructions to the patient, debilitating blurred vision after dilation is relatively uncommon. When tropicamide has been used for dilation, most patients recover reading ability within 1 to 3 hours, and virtually all patients completely recover accommodation within 4 to 6 hours. In many instances patients never lose the ability to read. Patients can therefore be reassured that any postdilation blurred vision will be transient and relatively mild.

Light Sensitivity

Mydriatic-induced light sensitivity can be problematic for many patients, especially those with cataracts or other opacities of the ocular media. Troublesome glare and reduced contrast sensitivity can limit visual activities after pupillary dilation. To help reduce sensitivity to light, the patient should have some form of protection from bright sunlight and other brightly illuminated environments. Commercially available mydriatic spectacles are designed specifically for this purpose.

Acute Angle-Closure Glaucoma

Although the prevalence of significantly narrow angles in the general population ranges from 2% to 6%, the risks of angle-closure glaucoma from the use of mydriatics have been estimated at only 1 in 183,000 for the general population and only 1 in 45,000 for the population older than 30 years. In the Baltimore Eye Survey none of the 4,870 subjects, aged 40 and older, whose eyes were dilated with 2.5% phenylephrine and 0.5% tropicamide developed acute angle closure.

When the benefit-to-risk ratio approach is applied to potential angle closure after pupillary dilation, the low risk of angle closure should not prevent the practitioner from using mydriatics when indicated. It was suggested that the greater danger derives from overlooking significant retinal disease by failure to dilate rather than from inducing angle closure by dilating. The discovery of peripheral retinal breaks in 6% of 250 patients without symptoms supports this statement. Also, dilation is especially important in the pediatric population. A study indicated that 25% of a group of pediatric patients had one or more posterior pole anomalies not detected by nondilated examination. By evaluating the anterior angle with slit lamp or gonioscopy, eyes predisposed to angle closure are readily identified, and appropriate precautions taken according to the guidelines were discussed previously.

Chapter 34 discusses the signs and symptoms and the definitive management of acute angle-closure glaucoma.

Systemic Complications

Although adverse systemic reactions to topically administered mydriatics can occur, dilation of the pupil is safe

340 CHAPTER 20 Dilation of the Pupil

and without adverse sequelae in the vast majority of patients. The risk of adverse reactions is greater in patients with certain systemic illnesses or in those using certain systemic medications. There have been few reports of adverse systemic reactions associated with the use of 2.5% phenylephrine in recommended dosages.The potential for adverse reactions associated with the use of 10% phenylephrine increases in patients with cardiac disease, systemic hypertension, type 1 diabetes mellitus, and idiopathic orthostatic hypotension and should be avoided (see Chapter 8).

In patients who are predisposed to adverse cardiovascular events, the use of tropicamide either alone or in combination with 2.5% phenylephrine provides satisfactory mydriasis while minimizing the risks of systemic complications. In addition, the use of low concentrations of drug, single applications, eyelid closure, and nasolacrimal occlusion minimizes adverse reactions in susceptible patients. Thus the combination solution made by mixing equal amounts of 1% tropicamide and 2.5% phenylephrine as previously described may have the added benefit of reducing the chances of an adverse reaction even further.

CONCLUSION

Pupil dilation is a safe and effective means of examining the internal health of the eye. Even instruments that are capable of being used with an undilated pupil often perform better when the pupil is dilated, especially in the presence of media opacities. Contraindications and serious complications are rare and, in the case of phobophobia and blurred vision, transient. The standard of care is such that a funduscopic examination, through a dilated pupil, should be advised for each patient at least once, or more frequently depending on their individual condition.

SELECTED BIBLIOGRAPHY

Amos JF, Semes LP, Swanson MW, et al. Pupillary dilation for aphakic patients, pseudophakic patients, and patients with cataract. Optom Clin 1991;1:188–194.

Anderson DR, Jin JC,Wright MM.The physiologic characteristics of relative papillary block. Am J Ophthalmol 1991; 111:344–350.

Benavides JO, Satchell ER, Frantz KA. Efficacy of a mydriatic spray in the pediatric population. Optom Vis Sci 1997; 74:160–163.

Bolt B, Benz B, Korner F, et al.A mydriatic eyedrop combination without systemic effects for premature infants: a prospective double-blind study. J Pediatr Ophthalmol Strabismus 1992; 29:157–162.

Classé JG. Pupillary dilation: an eye opening problem. J Am Optom Assoc 1992;63:733–741.

Gilmartin B,Amer AC, Ingleby S. Reversal of tropicamide mydriasis with single instillations of pilocarpine can induce

substantial pseudo-myopia in young adults. Ophthal Physiol Opt 1995;15:475–479.

Halpern JL. Routine screening of the retinal periphery. Am J Ophthalmol 1966;62:99–102.

Hatch SW. Clinicolegal aspects of practice guidelines for pediatric eye and vision examination. J Am Optom Assoc 1995; 66:501–509.

Hogan TS, McDaniel DD, Bartlett JD, et al. Dose-response study of dapiprazole HCl in the reversal of mydriasis induced by 2.5% phenylephrine. J Ocul Pharmacol Ther 1997;13:297–302.

Ismail EE,Rouse MW,DeLand PN. A comparison of drop instillation and spray application of 1% cyclopentolate hydrochloride. Optom Vis Sci 1994;71:235–241.

Keller JT. The risk of angle closure from the use of mydriatics. J Am Optom Assoc 1975;46:19–21.

Kudrna GR, Stanley MA, Remington LA. Pupillary dilation and its effects on automated perimetry results. J Am Optom Assoc 1995;66:675–680.

Locke LC, Meetz R. Sector pupillary dilation: an alternative technique. Optom Vis Sci 1990;67:291–296.

Loewenstein A, Bolocinic S, Goldstein M, et al.Application of eye drops to the medial canthus.Graefes Arch Clin Exp Ophthalmol 1994;232:680–682.

Martinez CE, Applegate RA, Klyce SD, et al. Effect of pupillary dilation on corneal optical aberrations after photorefractive keratectomy. Arch Ophthalmol 1998;116:1053–1062.

Newell FW, Ernest JT. Ophthalmology: principles and concepts. St. Louis: CV Mosby, 1974;3:150.

Nyman N, Keats EU. Effects of dapiprazole on the reversal of pharmacologically induced mydriasis. Optom Vis Sci 1990; 67:705–709.

Olsen CL, Gerber TM, Kassoff A. Care of diabetic patients by optometrists in New York state. Diabetes Care 1991;14:34–41.

Panton RW, Sulewski ME, Parker JS, et al. Surgical management of subluxed posterior-chamber intraocular lenses. Arch Ophthalmol 1993;111:919–926.

Parisi ML, Scheiman M, Coulter RS. Comparison of the effectiveness of a nondilated versus dilated fundus examination in the pediatric population. J Am Optom Assoc 1996; 67:266–272.

Patel KH, Javitt JC, Tielsch JM, et al. Incidence of acute angle-

in plateau iris syndrome. Am J Ophthalmol 1992;113: 390–395.

Pollack AL, Brodie SE. Diagnostic yield of the routine dilated fundus examination. Ophthalmology 1998;105:382–386.

Rebolleda G, Munoz FJ, Fernandez Victorio JM, et al. Effects of pupillary dilation on automated perimetry in glaucoma patients receiving pilocarpine. Ophthalmology 1992;99:418–423.

Ritch R, Lowe RF. Angle-closure glaucoma: therapeutic overview. In: Ritch R, Shields MB, Krupin T, eds. The glaucomas, ed. 2. St. Louis: CV Mosby, 1996: 1521–1531.

Rollins L. Repositioning of subluxated intraocular lenses. South J Optom 1993;11:19–20.

Sebag J. Seeing the invisible: the challenge of imaging vitreous. J Biomed Opt 2004;9:38–46.

Shaffer RN. Gonioscopy, ophthalmoscopy, and perimetry. Trans Am Acad Ophthalmol Otol 1960;64:113–127.

Shaffer RN. Problems in the use of autonomic drugs in ophthalmology. In: Leopold IH, ed. Ocular therapy: complications and management. St. Louis: CV Mosby, 1967;2:18–23.

Straub RH, Jeron A, Kerp L. The pupillary light reflex. 2. Prevalence of pupillary autonomic neuropathy in diabetics using age-dependent and age-independent pupillary parameters. Ophthalmology 1992;204:143–148.

van Herick W, Shaffer RN, Schwartz A. Estimation of width of angle of anterior chamber. Incidence and significance of the narrow angle.Am J Ophthalmol 1969;68:626–629.

Wesson MD, Bartlett JD, Swiatocha J, et al. Mydriatic efficacy of a cycloplegic spray in the pediatric population. J Am Optom Assoc 1993;64:637–640.

Wolfs RC, Hofman A, de Jong PT. Risk of acute angle-closure glaucoma after diagnostic mydriasis in nonselected subjects: the Rotterdam Study. Invest Ophthalmol Vis Sci 1997;38: 2683–2687.

Zangwill LM, Berry CC, Weinreb RN. Optic disc topographic measurements after pupil dilation. Ophthalmology 1999; 106:1751–1755.

Cycloplegic refraction remains a time-tested, reliable, and valid procedure for obtaining an accurate refraction.

Without cycloplegic drugs,determining the true refractive status of some patients would be fraught with error. Cycloplegia is essential for the proper diagnosis of refractive error in patients with refractive or accommodative esotropia, pseudomyopia, latent hyperopia, anisometropia, and amblyopia. Additionally, cycloplegic refraction is important in determining the refractive error in patients who are uncooperative, noncommunicative, inconsistent, or those presenting with functional visual deficits.

This chapter considers the indications, precautions, and contraindications associated with the use of cycloplegics in refraction.The chapter also discusses such clinical topics as selecting the appropriate cycloplegic agent, administration techniques, procedures for refraction, and general considerations for spectacle prescribing.

INDICATIONS AND ADVANTAGES

Cycloplegia plays a very important role in the refractive evaluation of young patients and thus should be performed during all first-time pediatric comprehensive eye examinations. In numerous clinical situations, cycloplegia can supply the practitioner with information that could not otherwise be obtained.

It is wise to perform a cycloplegic examination in infants, toddlers, and preschoolers because these children often have variable fixation with accommodative fluctuations. Clearly, as an objective method for determining refractive error in infants and young children, cycloplegic techniques are superior to those that are noncycloplegic. Not only is cycloplegic retinoscopy of infants and young children more accurate, it is also more easily performed because the examination does not depend on the patient’s fixation distance.

Cycloplegic examination is recommended for patients who are mentally impaired and for patients who are unresponsive or inconsistent in their responses to subjective refraction. Indeed, this may be the only way the clinician can determine the degree of refractive error, if any. In a

similar category are patients suspected of ocular malingering or hysteria. The clinician can avoid the unreliable patient’s subjective responses and arrive at objective refractive data through the use of cycloplegics.

In young patients with esotropia, determining the full amount of hyperopia is vital to prescribe plus-power lenses to relieve the effort placed on the accommodativeconvergence system and,in turn,bring the eyes into alignment. Although the full correction may or may not be prescribed, the value derived from the cycloplegic examination serves as a starting point that is then modified based on clinical judgment and experience.

In a more general sense, cycloplegic refraction is also indicated in young patients who demonstrate any type of strabismus. Not only does cycloplegia allow the clinician to diagnose correctly any accompanying refractive error, it also prepares the patient for a dilated fundus examination. All strabismic patients should have a thorough ocular health evaluation, especially when initially examined. This evaluation can exclude a pathologic etiology of the strabismus and can conveniently be incorporated into the examination after the cycloplegic refraction.

Nonstrabismic children with latent hyperopia are perhaps less obvious in their presentation, but this is another instance in which information gained by cycloplegic examination is essential to the ultimate management plan. In considering the amount of total hyperopia in conjunction with the patient’s signs and symptoms, a successful spectacle prescription can be determined more accurately.

The clinician may consider using cycloplegics in children who exhibit myopia for the first time. This approach allows the practitioner to rule out accommodative spasm (pseudomyopia) as the etiology.With the diagnosis of myopia established, future cycloplegic examinations need not be performed for a cooperative child. Similarly, prepresbyopic patients who have suffered a traumatic brain injury may manifest traumatic myopia, a form of pseudomyopia. Cycloplegic refraction aids the clinician in both the diagnosis and management of such patients.

344 CHAPTER 21 Cycloplegic Refraction

Box 21-1 Indications for Cycloplegic Refraction

Infants, toddlers, preschoolers Noncommunicative patients Uncooperative patients

Suspected malingering or hysterical amblyopia Patients with variable and inconsistent subjective

responses during manifest refraction Strabismic patients (particularly esotropes) Suspected latent hyperopia

Suspected pseudomyopia/traumatic myopia Amblyopia

Visual acuity not corrected to a predicted level Patients whose symptoms seem unrelated to the

nature or degree of the manifest refractive error

Cycloplegic refraction is also indicated for patients with active accommodative systems whose best corrected visual acuity in each eye is less than 20/20 and for whom there is no apparent reason for the decreased vision. It allows the clinician to determine whether uncorrected refractive error is responsible for the reduced acuity. This data may be particularly helpful in young patients with uncorrected antimetropia, latent hyperopia, or hyperopic anisometropia.

Amblyopic patients tend to have inaccurate responses during subjective refraction, thus necessitating cycloplegic evaluation. Cycloplegic retinoscopy reveals the true refractive error from which the clinician can base the patient’s refractive correction.

Finally, patients whose visual signs or symptoms do not correlate with the nature and degree of their manifest refraction may benefit from cycloplegic evaluation. A cycloplegic refraction aids in the differential diagnosis by helping to ensure that the patient’s problem is not refractive in nature.The clinician can then concentrate on other aspects of the visual system. Box 21-1 summarizes the indications for cycloplegic refraction.

DISADVANTAGES

Despite the previously mentioned advantages of cycloplegic refraction, it does have some disadvantages. Wide dilation of the pupil can create excessive spherical aberration in the ocular media, resulting in difficult retinoscopy and refraction. This situation is especially true when synergistic agents, such as phenylephrine, are used to permit fundus examination after retinoscopy. In addition, an allowance for ciliary tonus is usually necessary, and the clinician must consider this allowance when determining the appropriate refractive correction. Furthermore, because all cycloplegic drugs have potential side effects, caution must be exercised in their use.

Cycloplegics may blur vision for several days, and sunlight

or any bright light can be annoying, even with the use of sunglasses.

PRECAUTIONS AND

CONTRAINDICATIONS

Before administering a cycloplegic agent, the clinician should perform a preinstillation ocular evaluation. This evaluation not only protects the clinician legally but also provides valuable information regarding contraindications to the drug. Moreover, it furnishes certain baseline clinical information that may be unobtainable after cycloplegia.The following information and procedures, usually obtained as part of the comprehensive eye examination, constitute the minimum examination recommended before instilling a cycloplegic drug:

•Medical and ocular history, with particular emphasis on present medications, allergies, drug reactions, and previous eye examinations

•Visual acuity at distance and near

•Pupillary examination

•Evaluation of eye alignment

•Manifest (“dry”) retinoscopy/refraction

•Accommodative function, if desired

•Sensory-motor fusion, if desired

•Slit-lamp evaluation, with particular attention to the cornea, anterior chamber depth, and an estimation of the anterior chamber angle by shadow test or van Herick’s classification

•Tonometry, if possible

•Gonioscopy, if a shallow anterior chamber is observed or suspected

Often, some of these tests are not practical or possible

with infants or uncooperative children. Penlight estimation (shadow test) of the anterior chamber depth (see Chapter 20) can give the practitioner a reasonable idea regarding the safety of pupillary dilation without the necessity of a comprehensive slit-lamp evaluation.

Caution must be exercised when using cycloplegic agents in infants, because they are more susceptible to systemic complications due to their immature metabolism and excretion systems and their low body weight. The clinician should use the lowest concentration of drug that yields the desired cycloplegia.

Cycloplegia is contraindicated in patients with a history of angle-closure glaucoma.Atropine, in particular, should be used judiciously in patients with Down syndrome and in patients receiving systemic anticholinergic drugs because of potential adverse central nervous system side effects. Any known sensitivity to a specific cycloplegic agent can often be avoided by substituting another cycloplegic. In addition, obtaining patient or parental consent before administering cycloplegic agents is recommended. Finally, the patient and/or parent should be advised regarding the expected duration of dilated pupils, increased sensitivity to light, and blurred vision.

SELECTION AND USE OF

CYCLOPLEGIC AGENTS

All cycloplegics exhibit anticholinergic properties by blocking the response to acetylcholine at muscarinic receptor sites on the iris sphincter muscle and ciliary body. Clinically, this anticholinergic response manifests as some degree of pupillary dilation and cycloplegia.

To be clinically useful, cycloplegics should ideally possess the following properties:

•Rapid onset of cycloplegia

•Complete paralysis of accommodation

•Adequate duration of maximum cycloplegia

•Rapid recovery of accommodation

•Absence of side effects

Although no cycloplegic agent meets all these criteria,

some agents satisfactorily achieve the desired clinical purpose with a minimum of disadvantages. Table 21-1 lists the clinical characteristics of common cycloplegic agents in current use. The pharmacologic properties of cycloplegic agents are discussed in greater detail in Chapter 9.

Generally, when selecting cycloplegic agents for use in infants (12 months of age and younger), in patients with Down syndrome, and in patients with other central nervous system disorders, the lowest concentration of the appropriate drug is recommended. More specifically, when using tropicamide and/or cyclopentolate,the 0.5% concentration should be used rather than the 1% concentration for these patient populations.

COMPARISON OF CYCLOPLEGICS

The residual accommodation of various cycloplegics relative to 1% atropine was compared.The cycloplegic drugs were considered to be efficacious if the residual accommodation was less than 2.50D at the time of cycloplegic retinoscopy. It was found that two drops of 1% tropicamide was effective in 79% of whites and in 69% of African-Americans, as long as retinoscopy was performed within 20 to 35 minutes after instillation. If retinoscopy was performed after 35 minutes, the effectiveness of cycloplegia quickly became inadequate. One drop of 1% cyclopentolate was effective in 83% of cases with

examination between 20 and 40 minutes; however, when the examination time was extended to 60 minutes, the efficacy increased to 91%.When two drops of 4% homatropine and 1% hydroxyamphetamine were used, the cycloplegic efficacy was 40% within 40 minutes of instillation and increased to 59% if examination was performed 40 to 60 minutes after drug instillation. It was concluded that tropicamide was an effective cycloplegic agent as long as refractive error was assessed within 20 to 35 minutes of drug instillation. Cyclopentolate was found to be more effective than tropicamide and yielded a longer examination period before the cycloplegia becomes ineffective. The 4% homatropine was the least effective cycloplegic agent.

In another report, no statistically significant difference was found in refractive error between 1% cyclopentolate instilled three times within 15 minutes as compared with the traditional instillation of 1% atropine three times per day for 3 days. On the contrary, several other studies found significant differences in the mean cycloplegic refractive error when comparing 1% cyclopentolate to 1% atropine. One study found on average 0.66D more hyperopia in children younger than 6 years and 0.77D more hyperopia in children older than 7 years when using atropine versus cyclopentolate. Similarly, another study compared the cycloplegic effectiveness of 1% atropine versus a combination of 1% cyclopentolate and 1% tropicamide and found approximately 0.66D more hyperopia in the atropine group.Yet another study found that 1% atropine yielded on average 0.40D more hyperopia than 1% cyclopentolate in a population-based comparison of 1-year-old children.

The mean refractive difference in esotropic children between 3 months and 6 years of age was 0.34D more hyperopia when 1% atropine was used versus 1% cyclopentolate. This study implies that, clinically, cyclopentolate is sufficient for cycloplegic retinoscopy. However, in a subgroup of 22% of children, atropine uncovered an additional +1.00D or more of hyperopia. Almost all children in this subgroup demonstrated +2.00D or more on their initial cyclopentolate retinoscopy. Therefore the use of atropine may prove more important in children who have moderate hyperopia and esotropia.

346 CHAPTER 21 Cycloplegic Refraction

In recent years several studies investigated the effectiveness of cyclopentolate versus tropicamide in determining the refractive error of children and adults. One study found no statistically or clinically significant difference in refractive error measurements between 1% tropicamide and 1% cyclopentolate in healthy nonstrabismic infants between 4 and 7 months of age. Another study compared cyclopentolate versus tropicamide cycloplegia in children 6 to 12 years of age who were nonamblyopic and nonstrabismic and had low to moderate hyperopia (+0.25D up to +4.50D). There was no statistically significant difference between cyclopentolate and tropicamide refractive error values. The residual accommodation was also evaluated in these patients comparing subjective amplitude of accommodation to objective autorefractor measurements. Although accommodation was more effectively inhibited with cyclopentolate, the difference in residual accommodation was less than previous literature implied. Residual accommodation with tropicamide was 0.39 to 0.56D more than with cyclopentolate.These findings are in agreement with others that found objective measurement of residual accommodation after cycloplegia with cyclopentolate to be 0.57D in adults and 0.59D in children.The effects of cyclopentolate and tropicamide were evaluated on myopic children and found that the drugs revealed clinically equivalent refractive error results. Similarly, it was demonstrated that cyclopentolate and tropicamide showed no statistical difference in the cycloplegic refractive error of myopic adult refractive surgery patients.Thus tropicamide is clinically useful and effective for cycloplegic refraction of nonamblyopic, nonstrabismic, myopic, or low hyperopic children and adults.

CLINICAL PROCEDURE

Administration of Cycloplegic Agents

Many clinicians prefer to use a topical anesthetic before instilling a cycloplegic. The anesthetic diminishes the local stinging, irritation, and lacrimation that often accompany cycloplegic drops. Several authors have reported increased corneal drug penetration and therefore increased effectiveness of phenylephrine after topical anesthesia. Increased duration and effectiveness of cycloplegics may also occur after topical anesthesia.

The cycloplegic can be administered alone or as a combination cycloplegic–mydriatic solution to permit adequate binocular indirect ophthalmoscopy in neonates, infants, and young children after cycloplegic retinoscopy.

The combination drugs can be administered individually or as a combination solution.

The most widely accepted cycloplegic refraction regimen includes instillation of one drop of topical anesthetic followed by one drop of 1% cyclopentolate and one drop of either 2.5% phenylephrine or 1% tropicamide to facilitate dilation. After waiting 5 minutes, instillation of one

more drop of 1% cyclopentolate is recommended. If the patient is under 12 months of age the concentration of cyclopentolate and tropicamide should be reduced to 0.5%. Based on research, cycloplegic refraction may be performed after as little as 10 to 15 minutes in individuals with light irides and after 30 to 40 minutes in individuals with dark irides.

The cycloplegic, or combination cycloplegic–mydriatic solution, can be administered to the eye as a drop, spray, or ointment (atropine). As a drop, the chosen solution can be instilled in the traditional manner into the lower cul- de-sac with the eyelids open. However, in patients resistant to eyedrop instillation, the drop(s) can be applied to the medial canthus of closed eyes after which the patient is asked to open the eyes, allowing the solution to diffuse into the eyes. Using the medial canthus drop instillation method,one study evaluated the mydriatic effect of tropicamide in adults, whereas another study evaluated the mydriatic and cycloplegic effects of cyclopentolate in children. Both studies found that mydriasis and/or cycloplegia was equal using the traditional open-eyedrop instillation versus the medial canthus instillation. When children were asked to evaluate the comfort between these two drop-instillation techniques, 92% of the children surveyed reported better comfort with the medial canthus drop instillation.

Similar to the medial canthus technique, some clinicians found that sprays are particularly effective in treating children who are resistant to drop instillation in the usual manner. Several studies compared the efficacy of administering cycloplegic agents in a spray compared with the conventional eyedrop. Cycloplegic agents were instilled in four matched groups of children between 6 months and 12 years of age. Sixty-eight percent of the eyes were brown,24% of the eyes were blue,and 8% were classified as “other.” Eyedrops were instilled in eyes that were opened or closed and a cycloplegic spray was administered to opened or closed eyes. Residual accommodation was measured using dynamic retinoscopy or the push-up method at various times after administration of the medications. No statistical differences were reported in cycloplegic effect among the four groups. Another study found no statistically significant difference between a cycloplegic eyedrop instilled in opened eyes and spray administered to closed eyes based on objective refractive measurements in children between 18 months and 6 years of age, with 62% of the subjects having light eyes and 38% having dark eyes.This study also compared ease of administration of the two formulations and found the spray significantly better.

The practitioner must observe the recommended dosages for cycloplegic refraction.To overmedicate when maximum cycloplegia has been reached increases the probability of systemic drug absorption and the risk of side effects.The clinician using the spray method of instillation also needs to be diligent in preventing extraneous drug spray from getting into the patient’s mouth and/or