When a 3D eye model appears stiff during posing, it’s usually due to insufficient rigging (limited bone controls for subtle movements) or a lack of blend shapes (morph targets) for natural eye/lid adjustments.
Rigging that only handles basic rotation—without accounting for pupil alignment or eyelid tension—makes eyes look rigid instead of lifelike. Real eyes move with tiny shifts, not just big turns. Similarly, missing blend shapes for smooth expression transitions (like squints or gaze changes) prevent natural movement.
To fix this, add blend shapes for lid creases, gazes, or squints, or refine the rig with finer bone controls. Small tweaks here make eyes feel far more natural.