14 Apr Discovering the Gap in Your Vision
By Ace Meltzer
Close your right eye and stare at the small white square below. Move your device around a foot away from you. Without moving your eye, slowly move your device towards you. At some point, the large blue circle should fall behind your blind spot and disappear completely from view! Indeed, the circle should become part of the yellow background, a visual process known as filling in. Neat, right? You’ve just found your elusive blind spot, an area devoid of light receptors smack dab in the middle of your vision field.
To understand your blind spot, you must first understand how you see. The process starts with light passing into your pupil, the black dot in the center of your eye. As light passes through, the clear layer at the outermost part of your eye, the cornea, focuses the light so you can see clearly. The colored ring around it, the iris, has muscles that expand and contract to control the amount of light that enters the pupil, which helps you see even more clearly. Once light has entered your pupil, it passes through the lens of the eye, which focuses the light completely. After passing through the lens, light will hit the retina, the “wall” at the back of your eye. Photoreceptors, a specific kind of cell, absorb the light and transform it into electrical signals. These signals travel through the optic nerve and into your brain. Your brain then translates these signals into the images you see.
Do you see the little spot of lighter color in the eye diagram, right between the optic nerve and the vitreous? That is your blind spot, where your eye needs to have a clearing for the nerve to pass through. As such, there are no receptors there, which means these light-detecting cells will not send signals to your brain—and no image is formed!