Question

Which of the following statements is incorrect?

• A. The lens is held in place by ligaments attached to the ciliary body.
• B. Human eye adjusts the amount of light entering the eye by contracting the muscles of the iris.
  
• C. Human eye focuses light by moving the lens closer to or farther from the retina.
• D. The cornea participates in focussing of light.

Answer 1

The correct option is C Human eye focuses light by moving the lens closer to or farther from the retina.

Human eye focuses light by changing the focal length of the lens. Ciliary muscles around the lens hold it in place. When we try to observe a far away object, the muscles relax. This results in a pull causing the lens to flatten. To see closer objects, the ciliary muscles contract resulting in thickening of the lens. Human eye does not move the lens closer or farther from the retina.
The human eye adjusts the amount of light that enters by changing the diameter of the pupil. This is accomplished by the contraction or relaxation of the iris muscles.
65-75% of the focussing of light is done by the cornea, while the rest of the focussing happens when the light passes through the aqueous humor, the lens, and the vitreous humor.