How does the focal length of the human eyeball change?

Answer 1

The "eyeball" doesn't have a focal length, any more than the body of a camera or the tube of

a telescope have. It's the lenses (or mirrors) in the eye, camera, and telescope that have focal

lengths.

In the eye, the focal length of the lens changes when the shape of the lens changes ... becoming

flatter or thicker in the center. That change is accomplished by muscles around the circular edge

of the lens. They stretch the lens to flatten it, and relax to thicken it, when you shift your focus

to longer or shorter distances.

Answer 2

The focal length of the human eyeball remains relatively constant at around 17mm, as the shape of the lens adjusts to focus on objects at varying distances. This is achieved through the process of accommodation, where the ciliary muscles contract or relax to change the shape of the lens.