Look at the image above with the plus sign and the circle.
Look straight at the image, with your nose positioned somewhere between the plus and the circle.
Close your left eye and focus on the plus sign with your right eye. Do not look deliberately at the circle.
Now move closer to the image, slowly. Don't take your focus off the plus sign while you are doing this.
At some point between 30 - 35cm, the circle will disappear from your peripheral vision. And the brain will read the surrounding white colour to fill up the empty space.
This exact spot is the blind spot in your right eye.
The blind spot is a very small gap in the visual field of each eye. Generally, you don't notice this blind spot because the spot in one eye doesn't match the spot in the other eye. They overlap, allowing the eyes to compensate for each other. Each eye sends its own information to the brain, which is very efficient at filling in the missing information.
Light enters the eyes by passing through the pupil and reaching the retina at the back of the eye. The retina is made up of light-sensitive receptor cells which transmit information via the optic nerve to the brain where visual information is processed. There are no light-sensitive cells at the point where the optic nerve enters the retina, creating an area in the visual field of each eye where nothing is seen. The blind spot!
There are a number of simple activities to help demonstrate your blind spot.
To find your right eye's blind spot:
Close your left eye.
Hold your left thumb out in front of you, with your arm straight.
Look at your left thumb with your right eye.
With your left eye still closed, hold up your right thumb.
Place your right thumb next to your left thumb.
Keep looking at your left thumb.
Slowly move your right thumb to the right while looking at your left thumb.
When your right thumb disappears, you have found your right eye's blind spot.
To find your left eye's blind spot, close your right eye and look at your thumb with your left eye.
To find out how big your blind spot is, move your thumb around, up and down, and to the left and right.
The blind spot is a naturally occurring phenomenon in human vision and is usually of no concern. However, if it becomes noticeable and you experience changes in your vision, it may indicate a problem with the eyes. When nerves in damaged areas of the retina do not send visual messages to the brain, a person experiences a scotoma or blind spot. A scotoma could be linked to migraines or conditions such as glaucoma, retinal detachment, macular degeneration, diabetic retinopathy or HIV/AIDS-related eye problems.
Signs to be aware of include blank or dark spots in the field of vision which may come and go or move around in the field of vision, flashing lights, an increased or increasing number of floaters, or any other visual changes.
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A central scotoma is a blind spot that occurs in the centre of one's vision. It can appear in several different ways. It may look like a black or gray spot or it may be a blurred smudge or a distorted view when looking straight ahead. Scotomas may start out as a small nuisance and then become larger or there may be several blind spots or scotomas that block one's field of vision. A scotoma gradually impacts the ability to perform daily functions. The gray, blurred, distorted or black spot blocks out a person's face, words on a page, labels on a jar, or the petals of a flower. Seeing and recognising faces, watching television, reading and seeing numbers on the phone become difficult. Scotomas that develop in the periphery of one's vision are not as concerning as those that develop in the centre and do not interfere with daily tasks to the same extent.
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If you notice any signs or changes in your vision, schedule an appointment with your optometrist who will do a comprehensive eye examination and assess your visual field. The earlier the problem is detected, the sooner it can be treated and the better the prognosis for long term visual health. In spite of treatment central scotomas may not go away. Learning to adapt to this vision loss will help you maximise the vision you do have. Some tips to help one "see around" the scotoma include using more and better lights, utilising contrast to enhance light against dark or dark against light, and magnifying reading material with magnifiers, ebook readers or magnifying software. Switch to talking devices such as voice activated smart phones, books on tape, text to speech software, or talking watches.