The eye is one of the five sense organs of the human body, which allows us to view objects and sceneries around us. All other sense organs are important in their own way, but the eye takes precendence because we intake more than 80% of information from our eyes. The eye, like many other organs of the human body, is composed of various components, each critical to our vision. The article explores the basics of vision, its main types and some of the diseases that affect these different types.
What is Vision?
Vision is the ability of the eye to see and includes all the visual abilities and skills, such as contrast sensitivity, focus, accuracy, color vision, depth perception and more. Our vision is of different types and there are many factors that contribute to a perfect vision. A few of those include the field of view; movement, eye health, size of the eye, visual acuity, color perception, pigmentation, and even the number of rods and cones present in the eye. Even the slightest change may bring upon a huge defect in the vision. So lets explore the different types of vision and understand their importance.
Different Types of Vision
The two main types of vision include:
Central vision or Foveal vision
Peripheral Vision or Side vision
What is Central Vision?
The central vision of the eye is the vision that is formed at the center of the eye. This vision is the responsibility of the posterior of the retina, known as the macula. The macula is the photosensitive layer of the retina, which features high concentrations of photoreceptor cells that detect light and can send signals to the brain. The brain, along with other visual information, interprets these signals into images.
The central vision is our ability to see things straight ahead and with sharp detail, allowing a person to view shapes, colors, and details that are right in front of them. An example scenario would be the front view you have while driving, or seeing people’s faces while interacting. Central Vision is also dubbed as the Foveal Vision, as images are formed on the center of the field of vision.
What is Peripheral Vision?
The peripheral vision or indirect vision is the side vision of the eye that allows an individual to view the objects around them, without the need to turn their head or move their eyes. Peripheral vision helps view objects and scenes that lie outside of the central vision. This type of vision is the result of different nerve cells and rods located outside of the macula. As compared to animals, humans have a limited peripheral view. A normal visual field for a person covers 170 degrees around, while peripheral vision covers 100 degrees of this field.
Different photoreceptor cells are present in the eye, which are sensitive to light. In the human eye, these photoreceptor cells are most dense in the retina and least dense at the edges.
Fun fact: The peripheral visual field for humans extends 100° horizontally, 60° medially, 60° upward, and 75° downward.
Peripheral vision is further divided into three categories:
Far-Peripheral Vision: Beyond 60° till 100° to 110° of the visual field
Mid-Peripheral Vision: Beyond 30° but limited to 60° of the visual field
Near-Peripheral Vision: Beyond 18° till 30° of the visual field
Why is Peripheral Vision Important?
Peripheral vision is a vital component of the visual field. Other than allowing us to see thigns on our sides, it gives a sense of visual perception in crowded areas such as in traffic. Peripheral vision can help people view objects from the corner of their eye, including objects and movement outside of the gaze of the central vision. As compared to central vision, the peripheral vision plays a more effective role in viewing objects in the dark, due to a large number of rods in the peripheral retina.
Loss of Peripheral Vision
Peripheral vision loss is a common vision problem that can happen due to different injuries and eye diseases. Some of the leading causes of peripheral vision loss include:
Eye strokes and more
Optic Nerve Atrophy (ONA)
Compressed Optic Nerve Head
Glaucoma is the most common cause of peripheral vision loss. Glaucoma is not a single disease, but rather a group of eye diseases that cause damage to the optic nerve, due to the buildup of intraocular pressure.
Retinitis Pigmentosa (RP) is another group of rare genetic disorders that cause loss of night vision and peripheral vision. Retinitis Pigmentosa causes the cells in the retina to the breakdown, leading to significant damage and eventual loss of sight, if not treated.
Optic Neuritis is an inflammation of the optic nerve, which causes damage to the protective sheath of the nerve, and can cause blurring and the appearance of blind spots. Optic Neuritis is a common occurrence with infections and immune-related diseases.
Retinal detachment is the condition in which the retina splits from the layer underneath, forcing the fluid in the eye to collect behind the retina. Causes of retinal detachment include posterior vitreous detachment, injury to the eye, inflammation of the retina, choroidal tumors or some eye surgeries.
Optic Nerve Atrophy (ONA) is damage to the optic nerve or the degeneration of the nerve that can be caused by trauma, a decrease in oxygen, infection or other reasons. Optic Nerve Atrophy can affect the central vision, peripheral vision, or the color vision of an individual.
Optic Nerve Compressions occur when a mass such as a tumor or the build-up of puss or other fluid presses on the optic nerve. This pressure results in the loss of vision and may lead to eventual blindness.
Papilledema is swelling of the optic disc, due to intracranial pressure build up. Papilledema can cause blind spots, blurring of vision, and other types of visual impairment. If left untreated, papilledema can result in complete vision loss.
Head injuries, strokes, or any other kind of damage to the brain may cause pressure to build upon the optic nerve. This buildup of pressure may lead to the loss of peripheral vision or other complication. Injuries may also result in damaging parts of the brain that process images, leading to blind spots.
Eye strokes, also known as Retinal Artery Occlusion, are a result of clotting or the constriction of blood vessels in the eye. The restriction in blood flow causes a limited supply of blood in the eye, which may cause damage. Eye strokes can cause vision loss in the entire eye or affect some parts of the eye and vision.
Now that we know a few things that could damage our peripheral vision, lets talk about how to test your peripheral vision, at home. However, if you feel any discomfort in seeing things clearly or experience any kind of visual impairment, visit an eye doctor immediately.
Peripheral Vision Test
An easy way to test your peripheral vision is to create a DIY visual field exam, within the comfort of your home. All you need is a piece of cardboard or stiff foam board with the dimensions 24 inches by 12 inches or 60 centimeters by 30 centimeters. Place the board longitudinally closest to you. Determine the middle of the long side and place a pushpin into the center. Tie one end of a string to the pin and the other to a pencil. Extend this pencil tightly to the opposite edge of the board. Use this extended string to outline the bigger circle. Cut the board into the shape of a rainbow.
Trace a smaller circle onto the board using the same technique, to use as the cut out for the nose. Tape a cup to the bottom of the cardboard to use as a handle. Remove the string and the pencil. Secure the pushpin into its original position. The pushpin will serve as a focal point for the tester.
Cut out a few rectangular strips from stiff cardboard or paper, preferably colored, e.g., red, green and yellow, of 10 cm x 2 cm dimension. To add a little twist to the strips, cut out shapes on the strips, and note these shapes when testing out your peripheral vision.
Place the board on a flat surface with the nose cutout towards you. The board and the pin should be at eye level. Get a friend or a partner to hold the colored strips. Focus on the pushpin and ask your friend or family member to move the colored strips from one end of the rainbow to the other.
Note down or mark the points at which you can view the strip. Repeat the test at least three times for both sides, with varying strips. The test can help analyze your peripheral vision and allow you to note different colors, shapes, and details in your peripheral view.
Peripheral vision is just as important as central vision. Some might argue otherwise, but for the person who loses peripheral vision would never. Its like the old saying goes, “Prevention is better than cure”. So, instead of you waiting to get hit by some vision stealing condition (because eye damage is not reversible in some cases) and then start taking precautionary measures, it will serve you best if you adopt a generally healthy routine and try to avoid any scenario where any part of your vision is compromised, be it peripheral or central vision.
If you have additional questions about what peripheral vision is, here is an exhaustive piece of information on frequently asked questions about peripheral vision loss.