For a human eye, where u is the distance of an object from the eye, f is the focal length of the lens and v is the distance of image from the eye, which is the correct schematic graph ?

In the human eye, the distance between the lens and the retina (v) is fixed. To focus clearly on objects at varying distances (u), the eye performs a process called accommodation.

• According to the lens formula, 1/f = 1/v - 1/u. Since the image distance (v) is a constant physical dimension of the eyeball, the focal length (f) must change whenever the object distance (u) changes.
• The ciliary muscles adjust the curvature of the crystalline lens to modify f. When viewing distant objects, the lens becomes thinner (increasing f), and for near objects, it becomes thicker (decreasing f).
• Because v is constant and f is the variable that adjusts based on u, the schematic graph representing f versus u (Option C) correctly illustrates the eye's optical mechanism.