Abstract
This study aimed to characterize the impact of age on visual performance by analyzing monocular defocus curves across a wide age range in healthy phakic eyes. This observational cross-sectional study included 105 subjects, evenly distributed into seven age groups (20-65 years). Monocular visual acuity (VA) was measured at defocus levels from -3.00 D to +1.00 D in 0.50 D steps. Defocus curves were analyzed using four key metrics: baseline VA at zero defocus, curve slope, area under the curve (AUC), and the negative defocus cut-off point at 0.2 logMAR VA. A linear mixed-effects model assessed group differences in defocus curve shape, while non-parametric and parametric tests evaluated differences in AUC and cut-off points. We found that defocus curves remained stable up to 44 years of age, with a significant decline in baseline VA, curve steepness, and overall visual performance beginning at 45 years. AUC values significantly decreased with age, with a clear demarcation between younger (G1-G3; 20-44 years) and older groups (G4-G7; 45-65 years). The 0.2 logMAR cut-off point could not be reached in most younger subjects, indicating preserved accommodative capacity. In contrast, older subjects showed a progressive reduction in depth of focus, with statistically significant differences particularly between groups G4 (45-50 years) and G7 (61-65 years). Overall, these results indicate that defocus curve analysis reveals a functional inflection point in visual performance beginning at 45 years of age. This transition reflects early presbyopic changes, marked by reduced tolerance to defocus and diminished depth of focus. These findings support the use of defocus curves as a valuable tool to assess age-related visual changes beyond conventional distance and near VA tests.