Effect of Binocularity and Depth on Static and Dynamic Accommodation Responses in Young Children

The purpose of this study was to determine how binocular viewing and real depth influence accommodation in childhood, and whether these effects vary with refractive error (M), axial length (AXL), or future myopia.

Children with emmetropia (N = 92, 7.42 years, range = 6.58-8.33; cycloplegic M = +1.01 D, range = 0.62-1.42) completed accommodation testing every 6 months (3 years, 7 visits). In visits (V) 1 to 3, accommodation was assessed only under monocular conditions (flat stimulus). Beginning at V4, two conditions were added: flat binocular and 3D-depth binocular. This analysis includes V4 to V7, enabling longitudinal within-child comparisons across conditions. Static (40 cm) and dynamic (1-4 D sinusoidal) accommodation was recorded with an open-field autorefractor. Linear mixed-effects models compared responses among viewing conditions, testing moderation by age, M, AXL, and myopia outcome.

Binocular viewing increased dynamic amplitude (Amp; Δ ≈ 0.45 D, P < 0.01) and lengthened dynamic phase (Δ ≈ 0.12 seconds, P < 0.01) relative to monocular. It also modestly increased static accommodation response (AR) and reduced lag (both Δ ≈ 0.10 D, P < 0.01). Depth cues had no effect on dynamic accommodation (P > 0.25), but improved static responses with lower lag (Δ ≈ 0.09 D, P < 0.01) and higher AR (Δ ≈ 0.09 D, P < 0.01) under 3D viewing. M significantly moderated several binocular and depth effects (P ≤ 0.01), but AXL did not. Myopia outcome groups did not differ overall (P > 0.16), but showed significant depth × outcome interactions were found for lag (P = 0.02) and AR (P = 0.03).

Binocular and depth cues enhance accommodative performance in children and these effects vary with M (more hyperopic children show greater benefit from binocular and depth cues). Children who later became myopic demonstrated reduced benefit from depth cues, suggesting altered cue utilization may precede myopia onset.