WHAT IS A VISUAL FIELD?Find important information on what a visual field is, including its components and interesting features. As you read this text on your computer, you also are able to see other things around you: the computer keyboard, parts of the desk or table where your computer is located, perhaps a glass of juice or snack food off to the side, and possibly a nearby chair or other object in your visual field. In technical terms, our field of vision is the sum total of our line of sight at any given moment (also known as foveal vision) and our peripheral vision.
Simply stated, our line of sight is the only place in our visual field where we can see distinctly and clearly. It is what permits us to read, to watch television and movies, drive, and, yes, to work on the computer. The renaissance genius Leonardo da Vinci is credited with the discovery of line of sight. The expansive area of our visual field to the right and left of our line of sight is known as peripheral vision. But we pay a price for having a broad peripheral field. Objects within it are seen with less sharpness and detail. In fact, our ability to distinguish detail in our peripheral field of vision decreases as the angle distance from our line of sight increases. Animals have different fields of view, depending on the location of their eyes. For example, humans have their eyes located forward in the head. This gives us slightly more than a 180° horizontal visual field. Your line of sight is forward when you are driving a car. (Hopefully!) As you focus forward, your peripheral vision enables you to see what is happening to your left and your right, as well as up and down. But in order to see what is happening behind you, it is necessary to look in the rear view or side mirrors. On the other hand, most birds, along with mammals such as deer, rabbits, and squirrels, have their eyes located more to the side of their head, which gives them a 360° visual field, or one that is very close to it, and two separate lines of sight.
The way humans see is influenced by the fact that we have binocular vision. Most people find this concept confusing. The word binocular conjures up an image of the hand-held, dual-eyepiece telescope that is used for birdwatching and at sports competitions to see the action up close. Binocular vision, however, refers to a particular perspective or way of seeing the world. In binocular vision, the eyes are used together to produce a view that is stereoscopic or three dimensional (3-D). This means that we can see things in terms of their length, width, and depth. We share this feature with other animals, such as monkeys, hawks, cats and dogs.
The figure shows the area of visual overlap defined by fuchsia-colored lines. Within this region of overlap, three-dimensional vision (stereopisis) is possible. Outside of the region of overlap, it is not. The figure also shows the line of sight out to the focal point, defined by red lines. In technical terms, we call this fused (our brain combines both images into one), simultaneous (separate views of the same image are obtained simultaneously) binocular vision (both eyes are used). Binocular vision has three primary advantages over monocular vision, or vision in which only one eye is used.
The eyes must be pointed correctly and move in a coordinated manner in order to maintain stereopsis and singleness of vision. To achieve this, the position of each eye in its socket is controlled by six muscles called extraocular muscles. Small differences in the length of the extraocular muscles in the two eyes, their strength, or their points of connection can cause one eye to move to a different position in its socket relative to the other. This is known as phoria. A number of visitors have written to me asking for recommendations pertaining to eye-care products and books for obtaining more information. I have joined with Amazon.com to create a dependable resource for books and products. You can find these materials at the Eye-Care Store.
A scotoma is an area or island of reduced visual acuity surrounded by a field of normal vision. It also is called a blind spot. I have a scotoma. You have a scotoma. And so does every other person on the planet. This is because there is a location on the eye where the optic nerve connects to the retina where there are no photoreceptors. A photoreceptor is a specialized type of nerve cell found in the retina of the eye that is sensitive to light. The point of attachment is called the optic disc. We normally do not notice the scotoma in our visual field. Our binocular vision works in such a way that when both eyes are open, visual signals that are absent in the blind spot of one eye are provided from the other eye. This is because the optic discs are in slightly different locations on each eye.
Sure. Here's how to do it.
Cover your left eye and focus your right eye on the red square. Move your face slowly toward the computer screen, while still focusing on the red square with your right eye. At some point, the blue circle will completely disappear. (If you move even closer, it will reappear.) Now cover your right eye and focus your left eye on the blue circle. Repeat the process of moving closer to the computer and you will notice that the red square disappears. This test not only reveals your blind spot, it also demonstrates that neither the type of figure (square vs. circle) nor color (red vs. blue) matters. The eye simply cannot see in the area defined by the blind spot in our visual field.
Return from Visual Field to Glaucoma Diagnosis
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Technically speaking it is an imaginary optical line that stretches from a point of focus in the environment to the fovea inside our eye (highlighted in the diagram). Anything inside this line of sight can be seen with strong visual acuity. 
Our eyes are located forward in the head and some distance apart, with the nose serving as a divider in between. This attribute enables us to obtain two distinct views of the same object, each seen from a slightly different angle or parallax. Our brain combines these images to create a stereoscopic, three-dimensional reference in our visual field.
Can you show me how to find my blind spot (scotoma)?
