The eye and how it works: The first step in understanding glaucoma is to know some of the basics of the eye and how it works. Only if you have this knowledge can you discuss the condition and treatment of your eye with your eye doctor. Only by participating together can you and your eye doctor work as a team to protect your vision. Think of your eyes as a camera. Like a camera, the eye captures information about shape, color and movement and sends it to the brain in the form of impulses. The brain then converts this information into the images we see. Let’s take a look at the components of the camera that is the eye. The outermost layer of the eye is called the sclera. It is the white part of the eye and, although thin, is the eye’s strong protective shell. The part in front of the shell is called the cornea. The cornea is transparent and allows light to enter the eye through it. The cornea is much like the lens of a camera and provides most of the eye’s ability to focus light. The part of the eye that has color is called the iris. It not only determines whether your eyes look blue or brown, but also acts like the aperture of a camera. The iris contains muscles that control the size of the pupil and regulate the amount of light that enters the eye. The lens, located behind the iris, adjusts its shape and thickness so that the image seen can be focused on the retina. The retina then transmits the image as a nerve signal through the optic nerve to the brain, which processes these signals to form an image or visual image. The inside of the eye is filled with fluid. The gel-like substance called the vitreous humor occupies most of the space inside the eye. This space is called the vitreous chamber. The anterior chamber is bounded by the cornea, iris, pupil and lens. It is filled with an aqueous-like fluid called atrial fluid. The atrial fluid nourishes the cornea and lens, providing them with oxygen and vital nutrients, and also provides the pressure needed to maintain the shape of the eye. We call this pressure the intraocular pressure (IOP). As will be described in the following sections, maintaining proper pressure in the eye is very important to protect your vision. Measuring intraocular pressure is one of the methods ophthalmologists use to screen for glaucoma.