In the present study, we described the characteristics of monochromatic aberrations at 5.0-mm pupil size in 404 rural Chinese adults and investigated the relation between refraction, age, and HOAs. To the best of our knowledge, this is the first population-based study on monochromatic aberrations in a large sample of rural Chinese adults. It was found that coma, trefoil, SA, and third- and fourth-order aberrations were dominant among HOAs. Root mean square values of total HOAs, coma, trefoil, and SA significantly increased with age. However, there were no significant differences in HOAs among emmetropic, hyperopic, and myopic eyes after adjusting for age.
The present results showed that monochromatic aberrations varied widely among rural Chinese adults (0.077 to 1.254 μm), which was in agreement with previous studies.4 Mean RMS values of total HOAs were 0.296 ± 0.147 μm for all participants and 0.300 ± 0.017 μm for myopic participants in our study, which was smaller than that of younger myopic Chinese adults in Singapore (0.49 ± 0.16 μm).17 One important reason for the difference is that we measured aberrations at a smaller pupil size (5.0 mm) than they did (6.0 mm).17 It is well known that pupil size decreases with increasing age, thus reducing aberration magnitudes.35 The magnitudes of HOAs in our study were slightly higher than that reported by Wang et al.36 (0.229 μm, third- to sixth-order aberration at 5.0-mm pupil) on young myopic adults in Tianjin. Considering that aberrations increased with age6,7 and that our sample is composed of much older adults (49.9 years) than those of Wang et al.36 (21.9 years), our values of HOAs are consistent with theirs.
We found that RMS of total HOAs, coma, trefoil, SA, and third- to seventh-order aberrations significantly increased with age (Table 4), which is consistent with most previous studies.6,35,37,39–41 Atchison et al.42 only found a moderate effect of age on RMS of HOAs, which might be caused by a small refractive error range. Atchison and Markwell42 found that only the coefficient of horizontal coma demonstrated a negative correlation with age. In the present study, the coefficient of vertical coma (C3−1) and secondary astigmatism (C42) showed a significant negative correlation with age. However, only 2.7 and 3.7% of the variation are explained by vertical coma (C3−1) and secondary astigmatism (C42). The coefficient of spherical aberration (C40) showed a borderline correlation with age, which was in agreement with previous studies.6,35,37,41 Wei et al.17 found that only SA and vertical coma slightly increased with age. This may be accounted for by the fact that all their subjects were myopic (−5.23 ± 1.79 D, −0.75 to approximately −9.75 D) and had a relatively small age range (21.5 to approximately 52.8 years).
Interestingly, we found no significant differences in RMS of total HOAs, SA, coma, and trefoil between hyperopic, emmetropic, and myopic eyes after adjusting for age. This was consistent with some previous studies.43–45 Li et al.44 reported that ocular HOAs were similar among Chinese schoolchildren with different refractive errors (∼0.19 μm). Although these two studies focused on different Chinese populations, it seems that HOAs may play a weak role in the development of refractive error. However, some studies8,46,47 have reported higher HOAs in myopes than in emmetropes or higher HOAs in hyperopes than in emmetropes.48 We found that coefficients of SA were higher in hyperopic eyes than in emmetropic and myopic eyes (0.076 μm vs. 0.056 μm and 0.028 μm), which was in agreement with the findings of Hartwig and Atchison.48 The discrepancies among these studies may be explained by different subject groups, measurement techniques, and data analysis. In addition, it is not clear whether higher HOAs in these studies were merely the consequence of refractive error development. Therefore, longitudinal prospective studies on the same populations are necessary to investigate the effect of HOAs on refractive error development.
Strengths of the present study include a population-based survey among a large sample of rural Chinese adults. In addition, all participants grew up in villages and did farm work during their lives, which form an ideal condition to evaluate the effect of rural environments on refractive error. However, there are some limitations for this study. First, it is a cross-sectional analysis from which it is hard to establish a causative relation between monochromatic aberrations and refractive development. Second, other confounding variables such as time spent in outdoor activities and near work were not available for adjustment.
In conclusion, the current results demonstrated that ocular refraction in rural Chinese adults significantly increased with age. Higher-order aberrations in rural Chinese adults showed considerable variability and significantly increased with age. However, there was no difference in HOAs among myopic, emmetropic, and hyperopic adults. These findings suggest that HOAs may play a weak role in the development of refractive error.
No. 1 Dongjiaominxiang, Dongcheng District
This work was supported by the Major State Basic Research Development Program of China (973 Program, 2011CB504601), the Major International (Regional) Joint Research Project of the National Natural Science Foundation of China (81120108807), and the Beijing Nova Program (Z121107002512055). We thank Dr. Michel Millodot (School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK) for his help in revising this manuscript.
The authors declare that they have no competing financial interests.
Received November 2, 2012; accepted September 17, 2013.
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