Editor
We appreciate the letter by Galvis et al. (2016) regarding our recent publication investigating age cut-offs for cycloplegic refraction in teenagers and young adults. Indeed, we recognize that the use of two different cycloplegic agents introduces an inconsistency into our methodology in measuring cycloplegic effect. However, the decision to use tropicamide in older individuals was made after considering both the available evidence and pragmatic factors affecting our study population.
Many of our older subjects graciously gave off their time to participate in the study during work periods, and in these cases, we felt the period of cycloplegic recovery (up to 24 hours) was inordinate. In the authors’ previous experience in similar studies, this slow recovery has resulted in high rates of loss to follow-up. The more desirable pharmacokinetic properties (and safer profile) of tropicamide make this an easier agent to use with the working individual.
A review of the literature regarding the cycloplegic potential of cyclopentolate vs tropicamide will yield data finding statistical favour with the effectiveness of the former agent. However, what is much less clear is whether these differences translate to meaningful clinical effects – a reflection of the importance of interpreting effect size in statistical analysis. Accordingly, there are several studies that would suggest tropicamide is a useful cycloplegic agent in many circumstances (Egashira et al. 1993; Mutti et al. 1994; Owens et al. 1998; Manny et al. 2001; Nawrot et al. 2012). It is interesting to note that the largest genomewide association study of myopia utilized a participant reported rather than clinically based phenotype (Kiefer et al. 2013). Numerous novel (and replicated) genetic associations were identified using refractive data from customers of 23 and Me obtained without the assistance of tropicamide or cyclopentolate. It would appear that there is still some work to be carried out in determining the relative utility of both agents.
References
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