How does the eye respond to light?

When the eye is exposed to light, the primary response is for the pupils to constrict, a process known as the pupillary light reflex. This reflex helps to regulate the amount of light entering the eye, providing protection to the retina from excessive brightness. The constriction of the pupils also enhances visual acuity by allowing the eye to focus better under brighter conditions.

The constriction is controlled by the muscles of the iris, which respond to the intensity of light detected by photoreceptors in the retina. During this process, the brain processes visual signals indicating the presence of light and sends commands to the iris muscles to constrict, thereby reducing the size of the pupil.

In situations where the light intensity decreases, the pupils will dilate to allow more light in, which is the opposite reaction and is not applicable in this context. The thickening of the lens primarily focuses on adjusting for distance and does not directly relate to the eye's response to varying light conditions. Therefore, the correct answer reflects the specific physiological response of pupils to light exposure.