2.87 Eyes’ response to Stimuli

2.87 understand the function of the eye in focusing near and distant objects, and in responding to changes in light intensity

Focusing
Most of the bending of light is done by the Cornea
The Lens bends rays slightly to make an image clear and sharp

To focus on far objects the rays entering the eyes are almost parallel so less bending is required. The ciliary muscles relax tightening the suspensory ligaments so the lens is thin to focus the object on the retina

To focus on near objects, the rays are highly diverged so the cilary muscles contract, slackening the suspensory ligaments causing the lens to fatten focusing the light onto the retina

Light Intensity

The amount of light that enters the eye is controlled by the Iris this is done by changing the pupil size. The iris contains circular and radial muscles
In bright light

Circular muscles contract, radial muscles relax. Making the pupil smaller so less light can enter the eye. (Too much light can damage)
In Dim light

Circular muscles relax, Radial muscles contract. Making the pupil bigger to let more light into the eye.