How does an object moving away from an observer change its retinal image?

When an object moves directly away from an observer, it provides fewer visual cues of movement compared to an object moving across the field of view. However, the movement is perceived through changes in the size of the retinal image, specifically as the image shrinks.1

In addition to this change in retinal-image size, the human visual system utilizes other cues to perceive movement in depth, including:

• Changes in the convergence angle of the two eyes.1
• Adjustments in the eye's focusing mechanism.1
• Changes in the perceived haziness and brightness of the object.1

These cues collectively allow the brain to interpret the recession of an object even when it is not moving laterally across the visual field.1