Our results indicated that the values of SE and sphere component were significantly different before and after cycloplegia in both the tropicamide group and the cyclopentolate group. This suggests that it is necessary to perform cycloplegia refraction for Chinese young adults to obtain accurate refractive errors. No significant difference was found between autorefraction and subjective refraction with cycloplegia (p > 0.05). No significant difference was found in the changes of SE and sphere component between the cyclopentolate group and the tropicamide group (p > 0.05). This suggests that the cycloplegic effects of the two cycloplegic agents is comparable. The value of cylinder component before and after cycloplegia was not significantly different in our study.
Our results indicated that cycloplegic refractions were generally more positive or less negative than non-cycloplegic refractions in the cyclopentolate group and the tropicamide group. Our results were consistent with the previous studies10–12, 24. Mimouni et al10 reported 700 soldiers aged 18 to 21 years using 1% cyclopentolate and found the difference in SE was 0.46 D in myopes and 1.30 D in hyperopes. They concluded that it was necessary to perform cycloplegia in this age group (18–21 years). The Tehran Eye study12 analyzed participants with a wide age range from 5–95 years and showed that the mean difference in SE after using 1% cyclopentolate was around 0.4D in the 16–20 age group. In the study of Krantz, they used 1% tropicamide as cycloplegic agent and showed the difference in SE for participants (aged 22–39 years) was 0.44D. 11 Another study of 7793 healthy young adults (mean aged 20.2 ± 1.5 years) was conducted to compare autorefractions before and after cycloplegia9. The difference in SE with a mean of 0.83 ± 0.81D (median 0.63D) is larger than our findings 9. First, the distribution of cycloplegic refractions in population was different between their study and ours. Second, their study was based on a cycloplegic regimen of two drops of 1% cyclopentolate followed by one drop of 0.5% tropicamide. Only cyclopentolate or tropicamide was used in our study. Those two factors may explain the different findings.
We also found that more positive or less negative cycloplegic refraction was associated with the higher difference in SE, which was consistent with previous studies in children or young adults8, 10, 12, 13. Hypermetropes showed a larger difference in refraction before and after cycloplegia than myopes (1.08 ± 0.70D vs 0.35 ± 0.31 D in cyclopentolate group and 1.17 ± 0.73D vs 0.32 ± 0.26D in tropicamide group, p < 0.05 for all). It was speculated that accommodation capacity was stronger in hypermetropes than in myometropes. In the study of Sanfilippo, they reported that hypermetropes aged 13 to 26 years tend to exhibit greater differences in refraction after cycloplegia than myopes. 13 The Tehran Eye Study12 reported that in the < 25 years age group, the difference in SE between cycloplegic and noncycloplegic refractive errors was higher for cycloplegic hyperopes (0.65D), than for cycloplegic emmetropes (0.30D), and cycloplegic myopes (0.17D) (p < 0.001). The smallest difference in SE was for eyes with high myopia. The difference of SE value before and after cycloplegia was statistically significant in high myopes, with a mean value of 0.21D in cyclopentolate group and 0.22D in tropicamide group, which was of no clinical significance.
The findings of our study showed that there was no significant difference between autorefraction and subjective refraction with cycloplegia. In the cyclopentolate group, the mean difference in SE between autorefraction and subjective refraction after cycloplegia was 0.03D (p > 0.05). In the tropicamide group, the mean difference in SE between autorefraction and subjective refraction after cycloplegia was 0.06D (p > 0.05). Choong et al25 found that there was a tendency of over minus correction when the autorefractors were used under noncycloplegic conditions. No significant difference was found in mean SE between autorefraction and subjective refraction after cycloplegia. The Tehran Eye Study26 reported that mean difference between cycloplegic autorefraction and subjective refraction was 0.62 ± 0.54 D (p < 0.001) for participants with a mean age of 31.7 years (range 5–95 years) and inter-method differences significantly decreased with age (p < 0.001). There are two factors that could explain the differences in results with our study. First, their study was conducted on participants with age range of 5–95 years, which has a wider age range than ours. Second, subjective refraction was measured under noncycloplegic condition which contributes to more negative or less positive than cycloplegic refraction. We suggested that autorefraction provides an alternative method used in place of subjective refraction in Chinese young adults under cycloplegic conditions in epidemiological studies of refractive errors.
Our study proved that cyclopentolate had no statistically significant superiority in cycloplegia efficacy compared with tropicamide. This result is consistent with several studies that compare cyclopentolate to tropicamide on the basis of refraction results.20–22 In the study of 28 myopic adult refractive surgery patients (mean aged 35.4 years) in California21, they reported that there is no statistically significant difference between tropicamide and cyclopentolate cycloplegic refractions. The study published in 196122, demonstrated that cyclopentolate and tropicamide reduced accommodation to a similar level, but accommodation recovered much more quickly with tropicamide. Ihekaire et al20 found that the cycloplegic effect of cyclopentolate was stronger than tropicamide in 25 Black young adults aged 17 to 29 years with dark irises. The epidemiological refraction examination of young adults requires a rapid, safe, effective method of obtaining accurate refractive errors. In our study, no significant side effects of tropicamide and cyclopentolate were observed. The cycloplegic effects of two cycloplegic agents were similar for Chinese young adults with dark irises. Because of rapid onset cycloplegic effect and shorter duration of peak effect, we suggested that tropicamide can be considered as a viable substitute for cyclopentolate in refraction study of Chinese young adults.
Our research had several limitations. We performed cycloplegic refraction until the pupils are fully dilated in our study. However, there are some studies that found that the time of maximum cycloplegia was earlier than that of maximum mydriasis.27, 28 Thus, the time of the cycloplegic refraction performed may also vary from study to study.