Prior Topical Anesthesia Reduces Time to Full Cycloplegia in Chinese
Introduction
Accommodation is known to confound the types of refractive anomalies, such as latent hyperopia1 and pseudomyopia.2, 3 Whenever accommodation is suspected to play a role in causing visual problems, a cycloplegic refraction is mandatory.4
Cycloplegia is normally accomplished by topical administration of a diagnostic ophthalmic agent that paralyzes the ciliary muscle. The most commonly used agents are 0.5% and 1% cyclopentolate, and 1% tropicamide.5 Comparing the efficacy of these diagnostic agents for cycloplegic refraction, 1% cyclopentolate led to a lower amount of residual accommodation than 1% tropicamide.6, 7 However, these authors claimed that the differences were not clinically significant.
Cyclopentolate hydrochloride is a muscarinic antagonist that paralyzes the actions of the ciliary muscle.8 The drug is administered to the eye as a topical ophthalmic agent and it penetrates to the receptor sites through the cornea. When it is absorbed by the eye, it binds to the postganglionic muscarinic receptors of the parasympathetic nervous system. After this, the action of ciliary muscles is reversibly inhibited by the competitive binding of the drug to the muscarinic receptors. A latent period (the time between drug application and full cycloplegia) exists, and the inhibitory effect is commensurate with the availability of the drug.9 The latency is important information for clinicians, as it defines the time when measurement can begin. The accuracy of cycloplegic refraction is affected by the time of measurement. It is of utmost importance to understand the time course of cycloplegia to ensure a valid finding.
Topical anesthesia is sometimes used together with cyclopentolate, either to alleviate the unpleasant drug sensation of cyclopentolate10 or to shorten the waiting time before the measurement is conducted.11 It is believed that topical anesthesia shortens the time12 to maximum cycloplegia. While prior anesthesia has been widely practiced before cycloplegic refraction,11, 12 its effect on cycloplegia has not been documented.
Cycloplegic refraction is normally conducted when the amplitude of accommodation has ceased to decrease or when a full-sized pupil is observed.13 When the second criterion is adopted, practitioners should be aware that a full-sized pupil does not necessarily warrant complete cycloplegia.14, 15 If refraction is conducted on patients with active accommodation before cycloplegia is completed, the accuracy of the refraction might be questioned.
It has been reported that the time required to achieve full cycloplegia was longer in subjects with deeply pigmented irides.16, 17 Lovasik16 compared the accommodative loss in subjects with light-blue and brown irides under cycloplegia. The results showed that the brown irides group lost accommodation slower than the blue irides group. Chan and Edwards17 showed that people with heavily pigmented irides required more time to achieve full cycloplegia. In the literature, the recommended waiting time varies considerably between 20 and 45 minutes.5, 18 Whereas these data describe the clinical performance in Caucasians, these studies16, 17 also indicated a possible difference in cycloplegic performance among ethnic groups.
How long should the wait be before the measurements are made for the Chinese? To what extent does prior anesthesia affect the performance of cycloplegic refraction? The answers to these questions remain unclear. More information is required to understand the effects of prior anesthesia on cycloplegia.
The purpose of this study was to investigate the pharmacological response of the accommodative system to cycloplegics in a Chinese population when a prior topical anesthetic is administered. Our aim was to determine the minimum waiting time for cycloplegic refraction, with and without prior anesthesia of the cornea. The rate of accommodative loss, with and without a prior local anesthesia, was also compared.
Section snippets
Materials and Methods
Twenty-eight subjects were invited to participate in this study. They were all Chinese with dark brown irides and were recruited from the student community of the Hong Kong Polytechnic University; and their ages varied between 19 and 25 (mean = 21.14, SD = 1.98) years. Their spectacle refractions, with a back vertex distance of 12 mm, were determined before the commencement of the experiment. Subjects with high refractive errors (greater than −6.00 DS or −1.50 DC), and those having manifest
Baseline Amplitude of Accommodation
The baseline amplitudes of accommodation measured on the first and second visits were compared. The mean baseline amplitude of accommodation was 10.89 ± 1.47 D (mean ± 1 SD) and 10.93 ± 1.53 D for the first and second visit, respectively. The slightly higher mean amplitude of accommodation on the second visit was not significant (paired t-test, P = .78).
Effects of Local Anesthetics on Cycloplegia
After the drug administration, the accommodation clearly decreased with time and the results are represented in Figure 1. The diagram depicts
Discussion
Our data showed that the mean baseline amplitude of accommodation was 10.90 D in this young Chinese population. Edwards et al19 reported a lower but comparable value of 10.64 D for a similar age group. The slight difference could be attributed to the different experimental procedures: our mean chart luminance was set at 120 cd/m2 and their luminance was between 50 and 120 cd/m2. It is well known that a higher luminance level would enhance the visual performance,20, 21, 22 which might lead to a
Acknowledgements
The authors would like to thank Mr. J. Pang and Dr. C. P. Yu for their helpful advice on the instrumental set-up.
References (28)
- et al.
Spasm of the near reflexa spectrum of anomalies
Surv Ophthalmol
(1996) - et al.
Cycloplegic refraction in esotropic children. Cyclopentolate versus atropine
Ophthalmology
(1981) Accommodation without pupillary constriction
Vision Res
(1991)- et al.
Influence of topical anesthesia on tear dynamics and ocular drug bioavailability in albino rabbits
J Pharm Sci
(1975) - et al.
Refraction as a means of predicting squint or amblyopia in preschool siblings of children known to have these defects
Br J Ophthalmol
(1979) - et al.
A comparison of the effects of cycloplegics on accommodation ability for distance vision and on the apparent near point
Ophthalmic Physiol Opt
(1986) Pediatric refraction
- et al.
Comparison of cyclopentolate versus tropicamide cycloplegia in children
Optom Vis Sci
(1993) - et al.
The effect of cycloplegia on measurement of the ocular components
Invest Ophthalmol Vis Sci
(1994) - et al.
Cholinergic agents
General pharmacological principles
Topical and regional anesthesia
The ocular health examination
Diagnostic evaluation of strabismus
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