Also known as scotoma, a blind spot is a specific section in the eye/retina which does not have receptors that react to light. In lay man’s terms, a blind spot can be referred to as a tiny section in the eye without vision. Every human has a physiological or natural blind spot in the vision.
The blind spot was first observed and documented in mid-1600 in France by Edme Mariotte. During this period, doctors were of the opinion that the entry point of the optic nerve into the human eye was the retina’s most sensitive section. Edme’s discovery disproved this belief.
The blind spot is situated inside the eye at the upper end of the optic nerve. This nerve carries several nerve fibers from the brain to the eyeball. It enters into the eye through the back and scatters nerve fibers across the back, thus creating the retina in the process. The retina is a layer composed of light-detecting cells. The tiny circular entry spot of the optic nerve located at the back of the eye is known as the optic disc or optic nerve head. It does not have any light-detecting cells. Thus, each eye has a visual field with a small ‘blind’ gap.
The blind spot is situated 1.5 degrees under the horizontal and around 12 to 15 degrees temporal. Its width is approximately 5.5 degrees while the height is 7.5 degrees.
Most species of vertebrates have a blind spot in vision. However, in cephalopod eyes, which are somewhat identical to the human eye, the optic nerve accesses the receptors from the rear. Subsequently, no break is created in the retina, thereby preventing the development of a blind spot.
The visual field of each eye overlaps each other so as to overcome the effects of the blind spot. The brain efficiently uses different kinds of spatial data and information from the second eye to fill up any missing visual data. The process of guessing the missing information is continuously carried out by the brain. Because of all these reasons, we typically do not notice our blind spots.
Blind spots in vision: A study in detail
The human eye usually gives almost all the visual information to the brain to get a correct picture of the world. Human vision however comes with certain limitations. Certain creatures can detect infrared, while a lot of insects and birds can see UV. The human eye can however detect only visible light. As a result, humans have a limited view of the world; they cannot see the vibrant colors of certain flowers which appear plain in normal light but flash all its colors under UV light. Humans also cannot see the trails of urine scattered around by certain mammals. Additionally, unlike some birds and cephalopods, the human eye does not have the ability to differentiate between non-polarized and polarized light.
We usually assume that the things we see are the only things that are present. However, that is not true. Each human eye consists of a blind spot, but it does not prevent humans from successfully navigating across the world. The loss of vision is compensated by the brain which fills up the blind spots in vision.
Light goes through the pupil to enter the back part of the eye and hit the retina. This part of the eye consists of light-sensitive proteins which relay the sensations to the optic nerve, which in turn forwards such data to the brain. However, as the optic nerve directly attaches to the retina, a dark spot gets created at the spot of attachment. In most cases, the blind spot of one eye is compensated by the other eye which can clearly see the surroundings. However, if a person looks through just one eye, or if the blind spots in each eye overlap when checking out a particular thing, then the brain fills up the obscured area by merging it with the surroundings.
Method to detect a blind spot in vision
Take a blank piece of white paper and draw a colored circle on the left hand side and a cross on the right hand side. Now, shut the right eye and stare at the cross while simultaneously moving towards the pictures. When you reach a certain distance from the paper, you will notice that the circle has vanished. Stay at this distance, close the left eye and open the right eye. You will see that the cross has vanished. You may also conduct this experiment by using a colored piece of paper. In this, the cross or the circle will disappear at the distance of the blind spot of each eye and get replaced by the color of the paper.
Temporary blind spots in vision
People may sometimes suffer from temporary instances of blind spots in vision; it is usually marked by blurry vision and flashes of white light commonly referred to as ‘seeing stars.’ Such cases may occur due to the following reasons:
- Headache: Blind spots in vision or blurred vision can sometimes be a symptom of an impending instance of migraine headaches. It is more so if both the eyes exhibit vision problems. Such headaches may be severe or mild. Follow your health care provider’s instructions to treat them.
- Shifting of blood: The blood supply to the eyes and brain is usually reduced after or when exercising vigorously. This can result in vision disturbances such as blotchy colors and blind spots in vision. Patients may stop for a moment to regularize the blood flow and correct the vision problem. You may also completely stop the workout session for the day.
- Low levels of blood sugar: Vision deficits or blind spots in vision may also occur due to low levels of blood sugar. Glucose is the main source of energy production; engaging in prolonged or intense physical activities can eat up a large chunk of the glucose content in the body. Affected individuals may also suffer from dizziness, hunger, fatigue, and rapid heartbeat. It can be resolved by eating nutrients and protein-rich foods.
- Trauma to the head: Even minor blows to the head can result in the patient seeing stars, blurry vision, flashes of white light, and blind spots in vision, albeit for a short-term.