Our results revealed the optimal cutoff value of DCNVA for the assessment of early presbyopia. The diagnostic performance of NVA was high (AUROC > 0.70) with an optimal cutoff value of 0.00 logMAR for DCNVA. When classifying presbyopia using this cutoff value, subjective symptoms (awareness of presbyopia, high NAVQ score) and objective parameters (decreased accommodation) related to presbyopia were significantly correlated with the presbyopia status. These findings are clinically beneficial because the commonly used cutoff values of 20/40 and 20/50 at 40 cm may be insufficient to meet patients’ functional demands in the real world [10]. Considering comprehensive data on subjective symptoms and objective findings, we propose that an NVA of 0.00 logMAR (20/20) can be a good and clinically relevant cutoff value for defining early presbyopia.

This study indicates that a cutoff value of 0.00 logMAR for DCNVA corresponds to the conventionally proposed presbyopic status (defined as an accommodative amplitude of < 2.5 D). Remarkably, this cutoff value of 20/20 is much higher than indicated in previous studies [10]. For instance, the World Health Organization defines uncorrected presbyopia as the inability to read either N6 or N8 binocularly (corresponding to 20/40 or 20/50) at 40 cm [10]. Conversely, our current findings are generally consistent with those of a previous survey suggesting that presbyopia was recognized in over 80% of individuals when NVA was decreased to 20/20 [22]. McDonald et al. recently used a DCNVA of 20/25 as the cutoff value for mild presbyopia and non-presbyopia [11]. In this study, a cutoff value of 0.00 logMAR correlated well with presbyopia subjective symptoms; presbyopia awareness was 90.3% in those with > 0.00 logMAR but dropped to 26.2% in those with ≤ 0.00 logMAR. Similarly, the lowest quartile distribution of NAVQ scores (representing no difficulty in near-vision tasks) significantly decreased from 64+ % in those with ≤ 0.00 logMAR to 22% in those with 0.00–0.10 logMAR. Our data further support that an NVA of at least 20/20 is required to perform near-vision tasks comfortably.

Near pupillary diameter was significantly greater in the presbyopic group compared with those with non-presbyopia, suggesting that it could be a potential predictor of presbyopia at an early stage. A close correlation between accommodative amplitude and changes in pupil size was reported among ophthalmologically healthy subjects aged 26–52 years [23]. Additionally, the positive relationship between accommodative amplitude and changes in pupillary diameter (the difference of near and distance pupillary diameters) remains consistent, regardless of age [24]. However, as measuring pupillary diameter requires advanced ophthalmic instruments and our primary goal was to explore a simple, accessible method for detecting early presbyopia, we focused on NVA as an alternative indicator of accommodative amplitude in this study. Future studies should investigate the utility of near pupillary diameter in detecting early stages of presbyopia.

The discrepancy between subjective symptoms and objective findings related to presbyopia is being increasingly recognized. These differences are likely in people with low-to-moderate myopia since they can focus on objects without needing accommodation effortlessly than those with emmetropia or hyperopia [25]. Other factors, including contrast sensitivity, the presence of a cataract, and/or stability of the ocular surface, can also result in such gaps, accounting for the complexity of managing presbyopia [2]. When we defined presbyopia using DCNVA, the presbyopia group had a significantly lower accommodative amplitude than the non-presbyopia group, regardless of presbyopia awareness. Our results suggest that 20/20 DCNVA can independently detect early presbyopia. In exploratory analyses, the ROC curve was stratified by the awareness of presbyopia and found that the optimal cutoff values were consistent for both DCNVA (0.00 logMAR), regardless of presbyopia awareness. Thus, it is likely that a DCNVA of less than the optimal cutoff value can be an independent determinant of presbyopia, irrespective of subjective symptoms.

Epidemiological studies are likely to differentiate presbyopia-based symptoms. Holden et al. divided presbyopia into “functional presbyopia” (needing an optical correction added to the presenting distance refractive correction to see either N6 or N8 optotype at 40 cm) and “objective presbyopia” (needing a significant optical correction [ ≥ + 1.00 D] added to the best distance optical correction to see either N6 or N8 optotype at 40 cm) [26]. Nonetheless, these definitions were generally empirically driven, and an NVA of 20/40 (or 20/50) might be too low for the endpoint of presbyopia correction, given our current lifestyle [22]. Based on our recent findings, we propose an accommodative amplitude < 2.5 D (or DCNVA less than 20/20 as a substitute for accommodative amplitude) as a cutoff value of early presbyopia. Although further studies are necessary to replicate our findings in different regions and among wider age groups, our definitions should be more practical, at least in developed countries.

A close connection between good health and the workforce has been proposed [26] and correcting near vision is expected to substantially improve global work productivity [5]. Although several barriers exist, including limited access to healthcare services, insufficient medical expenditure, and poor-quality glasses [27, 28], lack of disease awareness is a major cause of untreated presbyopia, especially among young individuals [29]. A recent report from rural China shows that one-third of participants (28.8%) did not receive near correction because their presbyopic condition was unrecognized [29]. This is consistent with the fact that approximately 20% of participants aged ≥ 45 years in developed countries were unaware of their presbyopia, despite having difficulty in near-vision tasks [22]. Therefore, making a clear threshold for intervention for presbyopia and education on the disease state are urgent public health concerns even in developed countries, considering that wearing glasses can successfully correct presbyopia, thereby retaining the workforce in the previous trials [30].

This study has certain limitations. First, selection bias may have affected our results because we recruited healthy participants with excellent access to affordable treatment. Also, this study included younger individuals than in previous near-vision-related studies [26]. Nonetheless, our results are less likely to be affected by various confounding factors such as the presence of cataracts, decreased contrast sensitivity, aberrations, increased light scattering, dry eye, or other vascular and inflammatory-related diseases commonly seen in older populations. To minimize being confounded by non-nuclear cataracts (i.e., waterclefts or retrodots) that may affect the CDVA, we performed sensitivity analyses among participants with CDVA ≥ 20/20 and confirmed the optimal cutoff value of 0.00 logMAR for DCNVA for detecting early presbyopia (69.44% sensitivity, 85.37% specificity, with AUROC curves of 0.839 [95% CI, 0.771–0.907]). Although further studies are warranted to achieve generalizability, the current findings from relatively young populations would provide clinically relevant treatments for addressing productivity loss due to uncorrected presbyopia. Second, only a few participants presented advanced presbyopia. Accordingly, a larger study with a different degree of accommodation is required to determine the finer categorizations of presbyopia. Third, we did not collect several important parameters relevant to presbyopia, such as the near point distance, deviation of the habitual refraction from the best subjective refraction, contrast sensitivity, or habitual reading distance. Nonetheless, the DCNVA and accommodative amplitude are most commonly used in the literature [10]. Finally, our study did not include pseudophakic eyes. Thus, our optimal NVA cutoff value is only suitable for diagnosing phakic presbyopia; additional studies are required for those who have undergone cataract surgery.

In conclusion, we propose a new cutoff value for the assessment of early presbyopia: DCNVA < 20/20. Considering the significant socioeconomic loss resulting from uncorrected presbyopia, a simple, accurate, and easily accessible method for assessing early presbyopia is urgently required. Although further studies are required to replicate our findings, the vision threshold reflecting the functional demands of daily life should be much higher than that commonly used in near-vision research (20/40) [10], at least in developed countries.