URE is known to be associated with decreased quality of life and visual function difficulty. This association has been demonstrated in a variety of populations, using a variety of function assessment tools, including the NEI VFQ-25.7-10
However, to our knowledge, this is the first study to assess the association between correction of myopia, hyperopia, and astigmatism and difficulty with specific subgroups of visual function (near vision and distance vision, as measured by the NEI VFQ-25). As expected, we found that persons with corrected myopia reported better distance vision than uncorrected myopia, and persons with corrected hyperopia reported better near vision than uncorrected hyperopia. Unexpectedly, we also found that any type of RE, either corrected or uncorrected, was associated with significantly worse distance vision function compared to those without RE.
A previous study examining the association of correction, myopia, and hyperopia with quality of life found that only uncorrected myopia was independently associated with a decrease in overall visual function score as well as several independent visually dependent activities.7
In this study, using a different questionnaire that allowed us to score the subgroups of near visual function and distance visual function, we, too, found that subjects with uncorrected myopia have significantly more distance vision difficulty than subjects with corrected myopia or subjects with no refractive error. In contrast to the previous study, we also found that subjects with uncorrected hyperopia had significantly more near vision difficulty compared to those with corrected hyperopia, and that subjects with uncorrected astigmatism or uncorrected hyperopia had more near vision difficulty than subjects with no RE.
Quality of life improvement with correction of refractive error has previously been demonstrated.9,10
However, we found that both corrected and uncorrected RE of any type was associated with distance vision difficulty compared to subjects without RE, although URE was associated with stronger odds of distance vision difficulty than corrected RE of the same type. However, corrected RE remained significantly associated with distance vision difficulty compared to subjects without RE. This finding indicates that correction, at least as found in this study, may not be sufficient to restore distance vision function to the level of those without RE. It is not likely that this effect was due to under correction of RE, since, by definition, everyone with corrected RE had a visual acuity of 20/25 or better. It is possible that there is some aspect of distance visual function that is not completely characterized through visual acuity testing. If this is the case, the distance vision subscore of the NEI VFQ-25 may be able to capture some functional decrement that is not restored with correction, and that might otherwise be missed.
We found that subjects with corrected myopia report less near vision difficulty compared to those without RE (OR 0.78, 95%CI 0.68-0.93). We suspect this phenomenon may be caused by unmeasured near vision impairment in those without RE due to the development of presbyopia with age. People with no RE, and people with myopic RE, would likely both develop presbyopia as they grow older. However, people in this population of Latinos without RE may be less likely to seek eye care for deteriorating near vision alone. They may not be aware of the possibility of presbyopia correction with the purchase and use of reading glasses. On the other hand, when older persons with corrected myopia receive correction of their distance vision impairment, they are likely routinely evaluated for and prescribed additional correction for their developing presbyopia. This hypothesized disparity in the correction of presbyopia may explain the finding of significantly less near vision difficulty in corrected myopia compared to those without RE. Another possible explanation is that those with myopia may have good near vision with simply removing their spectacles, and may consider this as having no or little difficulty with near vision, compared to emmetropes who must still correct their presbyopia and consider the need for correction as indicating more difficulty with near vision. Although the association is not significant, this protective effect is also observed for corrected hyperopia.
We have previously shown that NEI VFQ-25 scores are influenced by demographic factors, including age, gender, level of acculturation, income, education level, as well as comorbidities such as diabetes and hypertension.13
In our analysis, we continue to confirm that these factors are independently associated with near and distance vision function regardless of RE type. Although the NEI VFQ was designed to be vision specific, it is clearly sensitive to other variables, including cultural factors. Thus, it is important to adjust for these, and likely, additional factors when predicting vision difficulty.
We acknowledge some limitations of this study, including the possibility of residual confounding. For example, there is a known association between depression and self-reported functional status, but information on depression status was not collected in our study.15
The absence of near visual acuity testing may be another limitation of our study. The no RE group likely included some subjects with presbyopia, which is consistent with the finding that those with corrected RE tended to have less near vision difficulty than subjects with no RE. If presbyopia had been taken into account, the protective effect of corrected myopia on near vision function may have been nullified. This study was carried out in a population that has limited access to eye care services, and may not be aware of the value even of reading glasses. This issue deserves further follow up.
Another limitation, not unique to our study, concerns the use of NEI VFQ in population-based studies. The distribution of vision function scores was highly skewed with a large ceiling effect. For this reason, we were unable to treat function score as a continuous variable, and decided to create three ordinal score categories by choosing two cutoff values a priori. As a result, people with subtly different levels of vision difficulty may be grouped in the same score category. Additionally, the near and distance vision subscores were based on just three questions, but the validity of these three item domains within our population has previously been examined.
We chose to use spherical error rather than spherical equivalent in this study, although the use of spherical equivalent is more common in studies of RE. In fact, the use of spherical error confers a unique strength to the classification of refractive error in our study. For example, an individual with myopia, but a large positive cylinder, might be classified as emmetropic by spherical equivalent. However, this individual’s myopia would be captured by the use of spherical error, leading to a more appropriate classification in this case. We also recognize that by not using cycloplegic refraction in those under age 50 years we may have underestimated hyperopia. This misclassification would have attenuated our finding of differences between those with hyperopia and those who were classified as emmetropia, thus suggesting that if anything, the differences we did find were even stronger.
Finally, the lack of a standardized definition for myopia, hyperopia, and astigmatism presented a challenge in the classification of subjects in this study. We chose cutoff values based on prior studies as well as expert advice. Certainly, different cutoff values may have produced different results. However, because we chose relatively conservative definitions for inclusion into a refractive error category, any bias in our results would likely be towards the null.
In conclusion, we found that all three types of RE in this study were associated with distance vision difficulty, but only uncorrected astigmatism and uncorrected hyperopia were associated with near vision difficulty. Importantly, we found that, in our population, correction of any type of refractive error is not entirely sufficient to restore distance vision function to the level of those without refractive error. This finding argues for more research investigating the underlying cause for ongoing dissatisfaction in distance visual function after correction of RE.
Uncorrected refractive error is a significant contributor to visual impairment in the United States. The burden of URE within the Latino populations, currently estimated at more than 48 million people, deserves particular attention.16
This study underscores the need for, and the potential positive impact of, programs aiming to reduce the prevalence of uncorrected refractive error in underserved populations such as in the Latino community.