THE HIDDEN GAP IN THE EYES

Everyone has a tiny imperfection in their eyes where the optic nerve leaves the retina and blood vessels enter it. This area is the optic disc or optic nerve head, which contains no light receptor cells, making it insensitive to light. Without photoreceptor cells, no visual information can be captured by the eye and no message can be sent to the brain which usually processes and interprets visual information. This is the blind spot. The blind spot is relatively small, measuring about 1.5 millimetres in diameter. Despite its small size, its impact on vision is significant because it creates a gap in the visual field.

The blind spot of the right eye is located to the right of the centre of vision and vice versa in the left eye. Most of the time we don’t notice the blind spot and it rarely affects our daily activities, because the blind spots of the two eyes are in different parts of the visual field. Each eye sends its own information to the brain, which merges the input from each eye, effectively eliminating the blind spots. The brain also has the ability to fill in missing information and seamlessly integrate it from areas surrounding the blind spot. This process relies on patterns, colours, and textures to fill in the gap, creating the illusion of a continuous visual experience.

Because of the compensatory mechanisms of the eyes and brain, we are unable to perceive the blind spot with both eyes open. Even with one eye closed, it can be difficult to detect it subjectively. However, there are a number of simple activities that can help demonstrate the blind spot. In one activity, your hands can be used to find each of your blind spots, as follows:

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, repeat the process closing the right eye and moving the left thumb instead of the right. To find out how big your blind spot is, move your thumb around, up and down, and to the left and right, and notice when it disappears.

While the blind spot is a naturally occurring phenomenon that generally goes unnoticed in everyday life, it can have implications in activities that require precise visual awareness, such as driving. The term "blind spot" is used in driving to refer to areas around a vehicle that the driver cannot see directly through mirrors. Awareness of these blind spots is crucial for safe driving, as it helps drivers understand the limitations of their visual field and encourages the use of other techniques to ensure safety on the road.

Changes in the size or position of the blind spot can indicate underlying health or vision issues, such as glaucoma, retinal detachment, macular degeneration and diabetic retinopathy. If there is damage to nerves or blood vessels in the retina or optic nerve, visual messages may be unable to be sent to the brain and vision loss may occur.

Warning signs include blank or dark spots which may come and go or move around in the field of vision, flashing lights, floaters, loss of vision and sometimes eye pain. Regular eye examinations that include tests for the blind spot can help detect these conditions early, allowing for timely intervention and treatment and a better outlook for long-term visual health.