Pupil reflex is a reflex action, carried out by the iris, which controls the amount of light that enters the eye. This involuntary response happens because too much light can damage the retina.
The iris is a coloured ring of muscle with a hole in the middle, which is called the pupil. To get to the lens, light must pass through the pupil.
The size of the pupil will change depending on the two sets of muscles in the iris: radial muscles and circular muscles.
|Radial muscles||Circular muscles||Size of the pupil||Amount of light entering the eye|
Accommodation is the process of changing the shape of the lens to focus on near or distant objects. This occurs through the contraction or relaxation of a circular ring of muscle called the ciliary muscle, which is connected to suspensory ligaments.
To focus on near objects, the ciliary muscles contract, so they become smaller in diameter. Also, the suspensory ligaments loosen so they don’t pull on the lens.
To focus on distant objects, the ciliary muscles relax, so they become bigger in diameter. Also, the suspensory ligaments are pulled tight so they pull on the lens.
|Distance of object||Ciliary muscles||Suspensory ligaments||Lens shape||Refraction|
|Near||Contract||Loosen||Bigger/spherical||Light is refracted strongly onto the retina|
|Distant||Relax||Tighten||Flatter||Light is refracted slightly onto the retina|