Our eyes are responsible for us seeing the world the way we do. They are what makes us see colors, shapes, patterns, and anything else in the universe; but how do our eyes work? What enables them to function the way they do? Why can some people see better than others?

The Cornea

When light enters the eye, it first passes through the cornea. The cornea is a clear covering that protects the outer part of the eye from unwanted or harmful particles. The cornea is made up of five different layers: Epithelium, Bowman’s layer, Stroma, Descemet’s Membrane, and Endothelium. The epithelium is the outermost layer of the cornea, and consists of cells that grow fast and easily regenerate. The next layer, the Bowman’s Membrane, has the job of protecting the stroma. The stroma, the middle and thickest layer of the cornea, consists of special cells that maintain the clarity and curved shape of the cornea. The descemet’s membrane is the outer part, or the shell, of the endothelium. The endothelium maintains fluids between the components of the stroma, keeping the cornea transparent.

The Pupil and the Iris

The pupil is the black circle at the center of the eye. The pupil is a hole that light enters the eye through. The iris is the colorful covering that surrounds the pupil. The iris expands and contracts based on the amount of light entering the eye. This makes the pupil larger or smaller. When there is a lot of light entering the pupil, the iris shrinks to make the pupil smaller so that too much light does not enter the eye. When there is little light entering the pupil, the iris expands to make the pupil bigger so that more light can enter the eye. This helps our eyes adjust to brightness or darkness.

The Lens

After light enters the eye, it passes through a natural lens in the eye. The lens is made up of transparent, flexible tissues. The lens’s job is to focus all light rays onto the retina, which is an area in the eye where the light rays get transferred to the brain. The lens changes its curved shape to focus on objects that are nearby or far away. By doing this, light rays are still focused on the retina.

The Retina and the Optic Nerve

The retina is made up of light-sensitive tissues that cover part of the eye. The retina converts light rays into electrical impulses. These impulses are carried to the brain by the optic nerve, which is a type of chord that connects the eye to your brain. The brain finally interprets these impulses as an image.

Rods and Cones

Rods and cones are the two types of photoreceptor cells located in the retina. These are the cells responsible for converting light rays into electrical impulses.

Rods are the specialized cells that provide peripheral vision(side vision), darkness adaptation, and are sensitive to motion or movement. Rods also help you see in low light condition.

Cones are specialized cells that provide the detail and sharpness in the images you see. Cones are also responsible for you seeing colors, and they specialize in central vision. Cones help you see in daylight conditions when there is a lot of light.

The Vitreous

The vitreous is a transparent, jelly-like substance that fills the eye and keeps it in its round shape.

 

How do People Become Nearsighted and Farsighted?

People who are nearsighted have trouble seeing things that are far away. People who are farsighted have trouble seeing things that are close or near, like reading a book.

When at least one eye of someone’s is longer or shorter than normal, they become nearsighted or farsighted. When an eye is longer than usual, light rays become focused in front of the retina. This causes the brain to have trouble interpreting images that are far away. Someone with an eye or with eyes longer than usual is nearsighted, and has trouble seeing far away. When someone’s eye or eyes are shorter than normal, light rays become focused behind the retina. The brain has trouble interpreting images that are close up because of this, and people with eyes shorter than normal are farsighted. They have trouble seeing things close up.

We solve nearsightedness and farsightedness problems by adding another lens to bend light rays even more; only this one is man-made. Glasses with concave lenses make light rays focus at a farther point, and are used for nearsighted people(people who have longer eyes) Glasses with convex lenses make light rays focus at a closer point, and are used for people who are farsighted(people who have shorter eyes). Based on the length of one’s eye, the lenses of one’s glasses are more or less curved.