Why can depth not be directly represented on the retina?

Depth cannot be directly represented on the retina because the retina is a flat, two-dimensional surface. The images formed on the retina are two-dimensional projections of the three-dimensional world around us. This means that while the retina can capture height and width information, it cannot inherently convey depth information.

Depth perception arises from various visual cues and mechanisms, such as binocular disparity (the slight difference in images seen by each eye due to their horizontal separation), monocular cues (like perspective, motion parallax, and occlusion), and the brain's processing of signals from both eyes. However, the physical characteristics of the retina itself, being flat, limit its capacity to convey depth. Thus, the correct answer highlights the intrinsic limitation of the retinal structure in representing depth information.