Our eyes are one of the most remarkable parts of our body. They help us take in the world around us by detecting light and sending information to the brain through the optic nerve. The brain then pieces these signals together to create the images we see every day.
The bones that form the eye socket, or orbit, are quite intricate. They include seven different bones: the maxilla, zygomatic bone, frontal bone, ethmoid bone, lacrimal bone, sphenoid bone, and palatine bone.
Our eyelids, which are made of soft tissue, act as protective covers for the eye. The white part we see is called the sclera, and it’s lined by a thin, clear layer called the conjunctiva. The cornea is the clear outer layer at the front of the eye. It stays smooth and moist thanks to tears produced by the lacrimal gland. Right behind the cornea is a small space called the anterior chamber, which is filled with a fluid known as aqueous humor.
The colored part of the eye is called the iris, and it determines whether someone’s eyes look brown, blue, green, or hazel. Inside the iris are muscles that control the size of the pupil—the dark circle at the center. The pupil adjusts its size automatically to let in the right amount of light. When it’s bright, the pupil gets smaller so we aren’t overwhelmed by light. In a dark room, it widens to help us see better. These changes happen because of tiny muscles called the sphincter pupillae and the dilator pupillae, which work without us having to think about them.
When light enters the eye, it first passes through the cornea and the aqueous humor. Then, it goes through the lens, which focuses the light, and into a gel-like substance called the vitreous humor. This jelly helps the eye keep its round shape. After passing through all these layers, light finally reaches the retina, which is a special layer full of cells that react to light and turn it into signals for the brain.
In the retina, there are two main kinds of light-sensitive cells: rods and cones. Rod cells help us see in low light and are mostly found around the edges of the retina, giving us peripheral vision. Cone cells, which are concentrated in the center area called the macula, let us see colors like red, green, and blue. There are about 120 million rods and 6 million cones in each eye!
These photoreceptor cells turn light into tiny electrical messages. These messages travel along the optic nerve to the brain. There is one spot on the retina, called the optic disc, where the optic nerve leaves the eye—this spot doesn’t have any light-detecting cells, so it creates a small blind spot in our vision.
Here’s a simple way to find your own blind spot:
Close your left eye.
Hold your left arm straight out and point your left thumb up.
Hold your right thumb up next to your left thumb.
Focus your right eye on your left thumb.
Keeping your gaze on your left thumb, slowly move your right thumb to the right. When your thumbs are about six inches apart, your right thumb will disappear. You’ve just found your blind spot!
