The first step in understanding diabetic retinopathy, glaucoma and low vision is to know how the eye works.

The eye is a complex organ that is very similar to a camera in the way that it captures and focuses light. The outer, white layer of the eyeball is the sclera, a tough, protective shell. The front, transparent portion of the shell is the cornea, through which light enters the eye. The cornea provides the eye with much of its light focusing power. The iris is the coloured part of your eye and is embedded with tiny muscles that dilate (widen) and constrict (narrow) the pupil to control the amount of light that enters the eye. The pupil is the opening in the centre of the iris.

Light rays are further focused through the lens, which adjusts its shape and thickness to focus the image onto the retina, a nerve tissue layer that lines the back of the eye. The retina contains millions of photoreceptors that capture light rays and convert them into electrical impulses. These impulses travel along the optic nerve to the brain where they are turned into images.

The inside of the front part of the eye is filled with a clear fluid called the aqueous. The fluid nourishes the lens, iris and cornea. In the center of the eye is a clear, jelly-like substance called the vitreous. This substance gives the eye form and shape.