We use our eyes every day—from the moment we wake up to the moment we close our eyes to sleep, we use them to navigate the world around us. You probably never think about your eyes unless you start to get a headache or misplace your glasses. But have you ever stopped a moment to think about how your eyes work?
Pupil You've seen your pupil—it's the black circular disk at the centre of your eye. The pupil is actually an opening that allows light to enter the interior of your eye and allows you to see straight forward. It dilates open and shut according to the amount of light available. This dilation maximizes your eye's ability to see during periods of low light and minimizes damage during periods with bright light. Iris The pigmented circle that surrounds the pupil is called the iris. This is the part of the eye that determines your eye colour. It's actually a membrane that lies between the cornea and the lens (more on those in a minute). The iris acts as a diaphragm for your pupil. It does the expanding and contracting to expand or shrink your pupil. Cornea This clear dome that covers the iris protects the iris and pupil from elements that might damage your eye. The cornea has multiple layers, which combine to create a strong barrier. The layers also regenerate quickly, so they can heal if any damage does occur. In addition to protecting the interior of the eye, the cornea also helps focus light more effectively. Lens Behind the cornea, in the interior of the sphere of the eye, lies the lens. The lens is a nearly spherical body that focuses light rays. Nearby ciliary muscles hold the lens in place and allow it to change shape in response to light. That way the lens can properly focus the light and deliver a clear image to the brain. Aqueous Humour Between the cornea and iris, a clear fluid called the aqueous humour fills the gap. It provides nourishment to the cornea and lens. It is split into two chambers: the anterior chamber in front of the iris, and the posterior chamber directly behind it. The two chambers provide structure to the eye so it maintains it shape. Periodically, the liquid drains from the eye and is replaced with new liquid. Sclera Surrounding the iris, pupil, and cornea, the outer surface of the eye is white. This is called the sclera. Although the sclera appears white on the outside, it's brown and grooved on the inside. The grooves properly attach the eye to its tendons. The sclera primarily serves to provide structure and protection for the eye, but it's flexible enough that the eye can move. Choroid The choroid is a series of blood vessels situated between the retina and the sclera. The blood vessels supply nutrients to various parts of the eye. Conjunctiva These form a thin layer of mucous membrane that covers the inner surface of the eyelids and the visible part of the eye, but not the cornea. The membrane keeps the eye moist, keeping it free from infection and damage. If the glands of the conjunctiva become infected, the eye could develop a condition called pink eye. Lacrimal Glands These glands lie on the outer corners of the eye. They are responsible for producing tears. Tears function to moisten the eye, flush out particles, and help the eye focus properly. Retina This sensory membrane lines the inner surface of the eye. The retina receives images the lens forms and converts them to signals that the optic nerve can transmit to the brain. The retina is made of rods and cones, which are photoreceptors that detect light. Macula At the back of the retina, opposite the lens, is a portion of cells called the macula. The macula absorbs light and helps the eye distinguish colours. The macula also controls central vision, which is necessary for most activities that require detail distinction. Fovea This area of the retina lies at the centre of the macula. It contains only cones and provides acute eyesight. Ciliary Body The ciliary body is a ring-shaped tissue that controls the eye lens's movement, holds it in place, and helps it maintain its shape. The ciliary body also helps produce aqueous humour, which keeps vision sharp and prevents glaucoma. Vitreous Humour This is the largest portion of the eye; it fills up the majority of the sphere of the eye. Vitreous humour is a clear jelly that helps the eye maintain its shape. It takes nutrients from the retinal vessels and ciliary humour. If any debris ends up in the aqueous humour, it can cause the eye to see "floaters" or light spots. Want to Learn More? The eye is a fascinating part of the human body. For more information about your eyes, eyewear, and more, check out our blog for regular updates.