Final answer:
The cornea's function is to refract light to help focus the image on the retina. It is the eye's outermost transparent layer and works with the lens to bend light properly, contributing significantly to vision.
Step-by-step explanation:
The function of the cornea is to refract light as it enters the eye, aiding in focusing the image on the retina. The cornea is a transparent structure forming the front part of the eye's outer covering. Contrary to options a, b, and c mentioned in the question, which refer to the iris, the shape of the lens, and the transmission of nerve impulses by the rods and cones, the cornea's primary function is related to the refraction of light, acting alongside the lens.
Light first encounters the cornea when entering the eye. Due to its curved shape and the refractive index of the materials it is made of, the cornea bends the light and thus contributes significantly to the eye's total optical power. After passing through the cornea, the light continues through the pupil (the opening within the iris) and then through the lens, which further fine-tunes the focus before the light ultimately reaches the retina. The retina contains photoreceptor cells (rods and cones) which convert the light into nerve impulses. These impulses are sent to the brain via the optic nerve, resulting in visual perception.