Ординатура / Офтальмология / Английские материалы / Ophthalmic Drugs Diagnostic and Therapeutic Uses 5th edition_Hopkins, Pearson_2007

pentolate in both eyes. Anisocycloplegia (a term originated by Beach (1942), who found it a phenomenon of fairly frequent occurrence) is the difference that might occur in the residual accommodation between the two eyes of the same patient to the same dose of a cycloplegic (often it amounts to about 0.5D, but exceptionally as much as 10.0D).

Rosenfield & Linfield (1986) proposed the use of what they termed ‘a distance accommodation ability’ measurement, in which negative spherical lenses are introduced until the patient is no longer able to clearly read a line of Snellen letters, as a measure of the degree of cycloplegia. They considered it an easier test to perform than apparent near point, especially on young children. It is interesting that the average minimum near and distance accommodation were not significantly different for 1% cyclopentolate as compared with 0.5%. Invariably, the residual accommodation was again found to be less in these eyes than the homatropine recordings, whereas anisocycloplegia might well occur in either eye.

Stolzar (1953) – in a further series (this time of 80 patients) – using two drops of a 0.5% solution of the original American proprietary brand of cyclopentolate hydrochloride (Cyclogyl), found an average residual accommodation after 1 hour of 1.03D. His results (with average residual accommodation measured after correction of any distance refractive error) were as shown in Table 6.2. Further analysis of this range of residual accommodation is also interesting (Table 6.3).

Table 6.3 Residual accommodation

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the conjunctival sac produce a full mydriasis in about 15 min, the pupil returning to normal in 8–9 h if no miotic is used to counteract the pupillary dilatation.

To produce cycloplegia, two drops of the 1% solution are instilled into the eye, allowing a 5-min interval between each drop. The full cycloplegic effect is achieved in about 30 min, when the retinoscopy is performed. If the examination has to be delayed beyond 35 min, because of the very brief maximal effect of the cycloplegia, a further (third) drop of the 1% solution should be used. Complete recovery of the accommodation usually occurs within 6 h and reading is generally possible after 2–4 h from the time of the initial instillations.

Excellent cycloplegia (with residual accommodation below 2.00D) is usually obtained, according to Gettes & Belmont (1961), following the procedures outlined above. However, due to the very brief duration of maximum effect, a third drop is not infrequently necessitated in routine practice. In a series of 193 patients, Gettes & Belmont (1961) were able to examine only 60% of these during the 20to 35-min interval when cycloplegia was maximal, and 40% had to receive the third drop. However, as Havener (1978) emphasizes, the great advantage of tropicamide is its rapid action and short duration, the patient having fully recovered from cycloplegia in 2–6 h, and these very qualities also make it a most useful mydriatic in its weaker concentration of 0.5% (Smith 1971). The speed of onset allowed Harding (1970) to see more patients in his working day and the short duration of action allowed patients to return to work within 2 h.

However, Milder (1961) did not find using two drops of the 1% solution to be as satisfactory a cycloplegic as the same number of drops of a 1% cyclopentolate or a 5% homatropine solution. He instilled tropicamide in one eye and cyclopentolate or homatropine in the other. In a series of 50 consecutive cases (100 eyes) he found better cycloplegia produced by the cyclopentolate in 23 out of the 25 cases and homatropine in 20 out of 25 cases in comparison to the tropicamide instilled in the second eye in each case. Thus, in only seven (five with homatropine in the other eye and two with cyclopentolate in the other eye) of the 100 eyes was tropicamide superior in its cycloplegic effect to these other drugs. In children in particular, Milder’s results indicated a poor paralysis of the ciliary muscle; in the six cases in this series up to the age of 9 years an average of 6.25D of residual accommodation was present after 30 min, and in 20 cases from 10 to 14 years this reading was still averaging 3.65D. Tropicamide would therefore appear to be a relatively inadequate cycloplegic for use with children. This was confirmed by Hiatt & Jenkin (1983), who found that tropicamide was less effective as a cycloplegic for preschool esotropia.

In some countries, a mixture of tropicamide and phenylephrine is marketed as a fast-acting cycloplegic and mydriatic. Lovasik & Kergoat (1990) compared this mixture with tropicamide alone and found that although a deeper cycloplegia was obtained with the mixture, the residual accommodation present after 20 min was too much for most refractive purposes.

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is particularly important to assess the effect of the proposed correction on the patient’s binocular status. Each prescription issued will be determined by the individual circumstances of the case, and it is therefore only possible to offer general guidelines on prescribing. In the case of esophoria accompanied by hyperopia, the aim would be to prescribe the minimum plus which would allow this heterophoria to become compensated.

In esotropia accompanied by hyperopia, the ideal is to prescribe that plus power that permits binocular fixation as demonstrated by the cover test. Both esophoria and esotropia might be of the convergence excess type and, as the degree of plus power required at near is greater than that for distance, it is likely to impair distance visual acuity. In such cases, bifocal or multifocal spectacles lenses might be appropriate.

It is unlikely that cycloplegia would be considered necessary in patients with exophoria or exotropia. Generally, the aim in these cases is to prescribe the minimum plus correction or a full minus correction. In some younger patients, a minus overcorrection might allow the compensation of the heterophoria or the attainment of binocular fixation in exotropia.

In every case, consideration must be given as to whether the patient will be able to tolerate the proposed prescription when it is compared to the present correction, if any.

USE OF CYCLOPLEGICS IN MYOPIA

Estimates suggest that the prevalence of myopia in young adolescents has increased in recent decades and is now in the region of 10–25% in industrialized Western societies and significantly higher – 60–80% – in Asian populations (Gilmartin 2004). These findings have stimulated various attempts to reduce the rate of progression of myopia in children including the use of topical ocular pharmaceutical agents. The rôle of other approaches, such as varifocal (progressive addition) spectacle lenses and rigid contact lenses, lies beyond the scope of this text.

The view that myopia develops as the consequence of prolonged exposure to nearpoint activities has prompted the regular application, over an extended period, of muscarinic antagonists. Many investigations have used animal models and, in 1965, Young studied the effect of atropine on the development of myopia in monkeys. Subsequently, the daily administration of atropine sulphate 1% in children was reported to reduce the rate of myopic progression (Bedrossian 1979, Dyer 1979). In a study in which atropine and cyclopentolate were compared, the latter was less effective in slowing the progress of myopia (Yen et al 1989).

The use of atropine in myopia induces the symptom of photophobia and the cycloplegia necessitates the use of spectacles, usually supplied as bifocals or varifocals, for close work. Because such problems can result in poor compliance, Shih et al (1999) evaluated the effect of 1.0%, 0.5% and 0.25% concentrations of atropine in controlling myopia, and concluded that 0.5% was the most effective.

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and salivary glands – a dry mouth is one of the earliest signs of atropine poisoning. The inhibition of sweat glands deprives the body of one of its methods of losing heat and, to compensate for this, there is a dilation of skin blood vessels, giving the patient the appearance of being ‘as red as a beetroot’. When CNS effects occur patients become as ‘mad as a hatter’.

CNS effects have also been reported following the use of cyclopentolate. In the majority of cases these effects followed the administration of a higher than recommended dose or a combination with other drugs CNS effects manifest themselves as confusion, difficulty in speaking hallucinations and ataxia. Fortunately there have been no fatal reports following these effects of cyclopentolate, and the patient is back to normal in a matter of hours.

These effects would appear to be dose related, as Cher (1959) used two drops of 0.5% with a 10-min interval between applications on 159 patients without producing CNS problems. Beswick (1962) used 2% cyclopentolate (not available in the UK) and noted hallucinations in a 9-year-old child. Binkhorst et al (1963) found that 2% cyclopentolate elicited reactions in four patients out of 40. One case has been reported in which CNS effects were seen after the use of 0.2% cyclopentolate (Carpenter 1967) but the patient had a history of chronic dementia.

From the above, it would appear that 0.5% cyclopentolate should be used whenever possible and cyclopentolate 1% should be used sparingly.

Problems in the gastrointestinal tract following the use of cyclopentolate in premature babies have been reported (Isenberg et al 1985). It was found that cyclopentolate 0.5% decreased gastric acid secretion while 0.25% did not. Bauer et al (1973) had earlier reported necrotizing enterocolitis following the use of cyclopentolate.

Homatropine, although less toxic than atropine, has produced problems in the past. Hoefnagel (1961) reported CNS effects such as ataxia and hallucinations in four children who had received six drops of homatropine 2% at 10-min intervals. Such a dose must be considered excessive and it is not surprising that problems arose.

In comparison with other cycloplegics, tropicamide is relatively free from adverse reactions. Wahl (1969) reported unconsciousness and pallor following one drop of 0.5%. As there have been no similar reports it would appear that the reaction is probably not drug related.

Allergic reactions can occur to many compounds. Atropine is probably the most notorious for producing reactions but cyclopentolate has also been implicated.

It might appear that the use of cycloplegics is potentially hazardous. If the precautions mentioned in this chapter are observed by the practitioner, then the risk of an adverse effect is minimized and will be a very rare occurrence. Optometrists who have maintained knowledge of and practice in the application of current first-aid procedures are clearly better equipped to recognize and deal with adverse reactions.

An unusual acute psychotic reaction following the instillation of two drops of cyclopentolate 1% in a 56-year-old woman has been reported (Mirshahi & Kohnen 2003). Immediately after the second instillation, the