Comment by philipswood

Most mammals are born with eyes that don't have a depth (and hence optical focus) set correctly for sharp focus on the retina.

The eyes need to use auto focus mechanisms to tune growth rates to correct for this. If something goes wrong you end up with vision problems.

The brain isn't born able to process visual images and needs training data. If the input from one eye is much inferior during learning image fusion it's input is just discarded and you end up with a lazy eye.