The sclera is the white of the eye and is made of dense, fibrous tissue that helps provide protection for the eye. The cornea is a clear extension of the sclera that covers the iris and helps to focus light by bending or refracting it.
The lens is the part of your eye that helps to focus incoming light. As light enters in through your eye, it actually enters through your pupil, which is right in front of the lens. The light will then hit the lens. Then, that light will be refracted (bent) towards the back of the eye.
The space between the lens and the cornea is filled with aqueous humor. Aqueous humor is a gel-like substance that helps maintain pressure, and also helps to transmit light to the lens. The outermost layer of the eye is the conjunctiva; it consists of mucus and blood vessels that protect the outside of the eye.
The pupil is the opening in the iris (the colored part of the eye that makes us "blue-eyed", "green-eyed", "gray-eyed", "hazel-eyed" or "brown-eyed"). The pupil can constrict or dilate to control the amount of light that enters the eye. If it's really bright outside and you're out, the pupil actually constricts to allow a less light in. Or if you're in a really dim room, your pupils will dilate to try and let more light in, so that you can see a little bit more clearly.
Within the eye, you can find the vitreous humor that helps to maintain pressure, support the eye, and helps the eye maintain its shape. The vitreous humor is similar to the aqueous humor, but it's found behind the lens and there's much more of it.
The retina is within the back of the eye; the lens focuses incoming light so that it shines on the retina. The retina contains rods and cones, which are photoreceptors that help to process this incoming light and allow you to see images and colors.
The fovea is an area in the retina where vision is the sharpest and is densely packed with all of these different types of photoreceptors. The optic nerve is the part of the eye that will then send information up to the brain for interpretation.
In the first step of vision, light enters as a wave through the pupil and the lens will focus it onto the retina. Then, rods and cones will convert the light signal into an electrical impulse conducted by the optical nerve to the brain.
Rods and cones, which are photoreceptors found within the retina, are connected to the neurons that send visual information to the visual cortex. The axons from neurons within the retina converge to form the optic nerves that carry visual information to the cortex to be processed within the brain.
Rods get their name because they have a rod shape to them. Rods are what allow us to see in dim light and allow for a more coarse perception.
Cones, on the other hand, contain a different visual pigment and they allow for daytime vision and for you to be able to see in bright light. There are actually three different types of cones: red, green, and blue.
If you think back to our rods, the reason that we can't see colors in the dark is that we can only see coarse images in the dark in black and white. In a dark environment, there isn't enough light to activate cones so we have a more difficult time processing colors.
Rods and cones contain visual pigments, which change their shape when different wavelengths of light are absorbed. Each color of light relates to a different wavelength of light. The wavelengths of red, blue, green, purple, or yellow are all different from one another. These visual pigments change shape, depending on the type of wavelength that's absorbed. Visual pigments contain a version of the protein opsin, plus retinal, which is derived from vitamin A.
Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND