The Human Eye

Parts of the eye, how it works, structure

The Human Eye

The human eye is an organ, which reacts to light and has several purposes. As a sense organ, the human eye allows vision. Rod and cone cells which are in the retina allow light perception and vision including colour differentiation and the perception of depth.

Retina and the Optic Nerve

The retina is a light-sensitive layer at the back of the eye. It covers about 65 percent of its interior surface. Photosensitive (it is an unusually high sensitivity to sunlight) cells called rods and cones (learn about rods and cones at the bottom of the page) in the retina convert incident light energy into signals that are carried to the brain by the optic nerve.

The optic nerve is the cable of nerve fibers, that carries the electrical signals from the retina to the brain for processing. The point of departure of that optic nerve through the retina does not have any rods or cones, and thus produces a "blind spot".

The Lens, Aqueous humor, Vitreous humor

The lens is composed of transparent, flexible tissue and is located directly behind the iris and the pupil. It is the second part of your eye, after the cornea, that helps to focus light and images on your retina.

Aqueous humor is a clear, watery fluid contained in a chamber behind the cornea that helps bring nutrients to the ocular tissue. It is made behind the lens and flows to all the way to the front of the eye, where it is drained by a tissue called the trabecular meshwork. Problems with the flow of this fluid can lead to problems with the pressure inside the eye.

The vitreous humor is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. It is often referred to as the vitreous body or simply "the vitreous".

Rods and Cones

There are two types of photoreceptors in the human retina, rods and cones. Rods are responsible for vision at low light levels (scotopic vision). They do not mediate color vision, and have a low spatial acuity. Cones are active at higher light levels (photopic vision), are capable of color vision and are responsible for high spatial acuity. The central fovea is populated exclusively by cones. There are 3 types of cones which we will refer to as the short-wavelength sensitive cones, the middle-wavelength sensitive cones and the long-wavelength sensitive cones or S-cone, M-cones, and L-cones for short.

By Myles Rattigan 😜