How Vision Works

The formation of visual images is a complex process, in which there are several critical steps. Each of these steps is equally important to the process; if any one does not function properly, vision will not be clear. The degree to which vision is blurry is dependent on the level of abnormal function. It is helpful to understand the steps involved in the production of vision, so one can better understand where and how vision can be affected.

The process of vision begins when an object is viewed. That object absorbs and reflects light in a particular manner that is unique to it. The light rays that are reflected from the object travel back to your eye and enter through the cornea. The cornea bends these light rays toward one another to help focus the light.

That light then moves toward the back of the eye. As it does so, it travels through the lens. Here, the light rays are again bent toward each other, which allows them to become further focused.

Ultimately, the light reaches the back of the eye, where the retina is located. Highly specialized cells in the retina, called photoreceptors, receive the light rays that have been focused by the cornea and the lens. These cells then produce a series of cell communications that culminate in the generation of a nerve impulse that travels from the retina to the optic nerve and, finally, to the brain, where the object being viewed is perceived and recognized by the brain. This is where the visual image is generated.

In order to have normal vision, light must be focused directly on the retina. Your central vision, which allows you to perceive fine detail, results from light being focused on the macula, the center of the retina. Although the cornea and lens are tremendous focusing structures, they do not always adequately focus light on the retina. They sometimes focus light in front of or behind it. In these cases, glasses or contact lenses are required in order to see clearly. Glasses and contact lenses, like the cornea and the lens, refract light in a certain way. They may bend light rays toward or away from one another, depending on the type of lens.

If an eye focuses light on the retina without the assistance of glasses or contact lenses, it is said to be emmetropic. In this case, one sees clearly without the assistance of glasses or contact lenses.

Illustration showing emmetropia where light rays are focused directly on the retina for clear vision.

Picture simulating clear vision at distance and near in an emmetropic eye.

© Vision Information Services, LLC, Mooresville, NC 2012