(i) The amount of light entering the eye is controlled by the involuntary muscles of the iris which regulate the size of the pupil.
Dim light
The radial muscles of the iris contract.
The circular muscles of the iris relax.
The pupil enlarges to increase the amount of light entering the eye.
Bright light
The radial muscles of the iris relax.
The circular muscles of the iris contract.
The pupil gets smaller to decrease the amount of light entering the eye.
(ii) The book is close to the eye so the lens must be made more convex to focus the diverging light rays on to the retina. The cilary muscle contracts. The suspensory ligaments are no longer under tension.
The lens become thicker and more convex focussing the light rays on to the retina.
(iii) The object is being viewed by both eyes at the same time. Each eye views the object from a slightly different angle, thus producing different images. The brain combines these images giving the perception that the object is three dimensional.