Fast and Slow Response of the Accommodation System in Young and Incipient-Presbyope Adults During Sustained Reading...

Objectives: To investigate the dynamics of accommodation during and immediately after a sustained reading task on a digital device across various age groups under monocular and binocular conditions. Methods: Seventeen subjects were selected and divided into three age groups: young adults (n = 4, age: 21.3 ± 3.2 years), adults (n = 4, age: 34 ± 3.56 years), and incipient presbyopes (n = 9, age: 45 ± 3.61 years). Dynamic accommodation and disaccommodation were objectively measured using the WAM-5500 open-view autorefractor during 2 min of distance fixation (Maltese cross at 6 m), 5 min of sustained near reading on a teleprompter app at the nearest readable distance, and 2 min of distance vision. Six sequential temporal landmarks were identified. Quantitative metrics for accommodation lag (AL), slope of slow accommodation (SSA), slope of slow disaccommodation (SSD), peak velocity of accommodation (PVA) and peak velocity of disaccommodation (PVD) were obtained as absolute values of spherical equivalent refractive (SER) change. Results: SSA, SSD, and AL were significantly and positively correlated with age (ρ = 0.75, 0.73, 0.51, respectively; p ≤ 0.038). For subjects under 45 years of age SSA and SSD increased quadratically with age, while for those above 45 years, both SSA and SSD decreased linearly. Linear regression of PVA and PVD with age indicated that the disaccommodation mechanism is faster than accommodation (slope = -0.15 and -0.23, respectively). PVA was significantly faster under monocular than binocular conditions (p = 0.124). Conclusions: Incipient presbyopes demonstrate a complex response in both accommodation and disaccommodation. The accommodation system responds quickly, but there is also a slower response that can provide up to an additional 1D of accommodative response during sustained near reading tasks. It is hypothesized that the crystalline lens exhibits hysteresis in returning to its unaccommodated state, due to its viscoelastic properties, which means it takes time to relax.