Research on Peripheral Vision

                Peripheral vision is the ability to see objects and motion to either side while looking straight ahead.  It is the blurry vision that’s outside the clear image of your focused, or conical, vision. If you’ve ever seen a shadow or movement to the side of your head, you’ve used your peripheral vision.  We will be explaining how the eye works, why you see peripherally, what’s going on in the retina, and what some of the problems with peripheral vision are.

            The human eye is a remarkable creation of God. It accommodates to changing lighting conditions and focuses light rays that are coming from various distances from the eye. When all of the components of the eye are functioning properly, light is converted to impulses and conveyed to the brain where an image is perceived.  Light rays enter the eye through a transparent layer of tissue known as the cornea. As the eye's main focusing element, the cornea takes widely ranging rays of light and bends them through the pupil.

          The lens of the eye is located immediately behind the pupil. It makes the delicate adjustments in the path of the light rays in order to bring the light into a focus upon the retina, the membrane containing photoreceptor nerve cells which lines the inside back wall of the eye.  The retina is the “seeing portion of the eye.”  It functions almost like a camera because it captures an image and turns the image into an electrical signal which is sent to the brain for interpretation.  The retina has two parts: the peripheral retina and the macula.  A good comparison of the retina would be to a circle with a bull’s-eye at the center representing the macula, which is very small. The large area, which surrounds the macula, is known as the peripheral retina and makes up 95% of the retina.

              The peripheral retina gives us side vision, which is called peripheral vision. When we see something out of the corner of our eye, we use the peripheral vision. This side vision does not allow us to see detail so it can’t be used to read effectively or perform tasks which require good vision.  However, peripheral vision is constantly used in everyday tasks such as driving a car.  

                The retina is more than just a macula and peripheral retina through, it also contains rods and cones.  These are the two types of photoreceptors in the retina. The rods are more numerous, some 120 million, and are more sensitive than the cones. However, they are not sensitive to color.

Rods are very sensitive (except to color), using a special photopigment called rhodopsin. They are responsible for our vision in the dark and are very efficient photoreceptors, at more than one thousand times as sensitive as the cones.  The optimum darkness adapted vision is obtained only after a considerable period of darkness, usually 30 minutes or longer, because the rod adaptation process is much slower than that of the cones.  While the visual resolution is much better with the cones, the rods are better motion sensors.  Since the rods predominate in the peripheral vision, it is more light sensitive, enabling you to see dimmer objects to the sides of your focus.  If you see a dim star in your peripheral vision, it can disappear when you look at it directly since you are seeing it through the fovea centralis, which is rich in cones, but less light sensitive. You can also detect motion better with your peripheral vision, but  the rods inside are good at that too. 

                Of course we know that nothing is perfect.  So what are some problems of peripheral vision?  Many times, people lose their peripheral vision.  A very common cause of peripheral vision is glaucoma.  Glaucoma is caused when too much pressure builds up on the back of the eye, which causes the eye to flatten out.  Other common causes of peripheral vision loss include, stroke, branch retinal vein or artery occlusions, ischemic optic neuropathy, and migraine.  Uncommon, or even rare, causes of peripheral vision loss include retinitis pigmentosa, choroideremia, gyrate atrophy, pituitary tumors, optic disc drusen, brain tumors and aneurysms, and tilted optic discs. Many other possibilities exist, but are even rarer.  Individuals with loss of vision on the periphery, or tunnel vision, retain clear central vision.  In some cases small areas of peripheral vision remain present, making it possible to detect movement and objects to help a person’s orientation. Typically, an individual with loss of side vision will not realize their lack of peripheral vision right away because the areas where there is no retinal cell activity are neither light nor dark. This can be compared with trying to see what takes place in a room behind your back. 

Treating peripheral vision loss can be difficult because of the wide range of causes, some of which cannot be treated at all.  However, glaucoma, one of the most common reasons for this vision loss can be treated in a few ways. Treatment usually starts with eye drops to help lower the pressure in the eye. Some eye drops do this by decreasing the production of fluid within the eye. Some eye drops try to open the drainage canal inside the eye to let more fluid out. There are many different eye drops that can be used. Sometimes, pills are used to decrease the production of fluid. Then, laser surgery is completed in a 5 minute procedure to try to open the drainage canal inside the eye. This procedure has no pain and is successful about 80% of the time. Some types of glaucoma respond better than others. Finally, glaucoma surgery can be performed which involves surgically placing a microscopic size hole in the eye to create a new drainage canal inside the eye. 

Most often, these procedures will be successful in restoring vision, including peripheral vision.  This only applies to glaucoma though, obviously there are many other reasons for peripheral vision loss that can’t be treated – gauging your eye out for example. 

Living without peripheral vision can be very difficult.  The lack of it can lead to accidents in cars, or even just walking around and running into people or things that you didn’t see coming.  Peripheral vision is directly linked to one’s reflexes.  For example, when a person sees an object coming toward them from the side they are using their peripheral vision.  That peripheral vision then causes their reflexes to kick in and to make the person duck or move out of the way.  Peripheral vision is indeed a wonderful blessing from God that should not be taken for granted or overlooked.  While peripheral vision is definitely cool, it is almost a necessity and its importance should not be underestimated. 

            While peripheral vision is not necessarily vital to one’s life, it certainly holds a great deal of relevance.  Now we can know for the most part how it works and hopefully no longer take it for granted.  As simple as seeing unclear objects to the right or left might be, the process our eyes go through is very complex, and we should all thank God that we are blessed with this ability, because some people obviously aren’t.  Peripheral vision is an interesting aspect of the human eye through how we use it, its development in the retina, and the defects that we sometimes encounter with it.

For more information on peripheral vision see these sources:

            http://www.retina-international.org/losspvis.htm.  Loss of Peripheral Vision.  Apr. 2001. Retina International. Feb. 2005

            http://www.exploratorium.edu/snacks/peripheral_vision.html.  Peripheral Vision, Exploratorium.edu.

            http://webexhibits.org/colorart/ag.html.  Peripheral Vision, Fauves Whitfeild, Web Exhibits.org.

            http://www.eyemdlink.com/Condition.asp?ConditionID=342.  Peripheral Vision Loss, Eyemdlink.com.