The exact size of a human blind spot is approximately 7.5° high and 5.5° wide.
Every human eye possesses a blind spot, also known as the optic disc. This is a small area within your field of vision that corresponds to the point where the optic nerve exits the retina. Since this region contains no photoreceptor cells (rods or cones), it cannot detect light, creating a natural "blind" spot.
Understanding the Dimensions
Based on information from November 9, 2022, your blind spot has specific angular dimensions:
| Dimension | Approximate Size |
|---|---|
| Height | 7.5 degrees |
| Width | 5.5 degrees |
These measurements refer to the angle of vision it occupies, rather than a physical distance, as its perceived size changes with distance from the object.
Why We Don't Notice Our Blind Spot
Despite its presence, you rarely notice your blind spot in everyday life due to several remarkable mechanisms:
- Brain Compensation: Your brain "fills in" the missing information using surrounding details and predictions, essentially ignoring the gap.
- Two Eyes Working Together: With two eyes, the blind spot of one eye is covered by the visual field of the other. The brain merges these two images, effectively eliminating the blind spot from your conscious perception.
- Constant Eye Movement: Even when looking at a fixed point, your eyes make tiny, rapid movements (saccades and microsaccades) that ensure different parts of the retina process the image, preventing any single part of the visual field from constantly falling on the blind spot.
Finding Your Own Blind Spot
You can easily demonstrate the existence of your blind spot with a simple exercise:
- Preparation: Draw two small, distinct symbols on a piece of paper, about 6-8 inches apart. For example, a small 'X' on the left and a small 'O' on the right.
- Position: Hold the paper at arm's length.
- Close One Eye: Close your left eye.
- Focus: Look directly at the 'X' with your right eye.
- Move Slowly: While keeping your right eye focused on the 'X', slowly bring the paper closer to your face.
- Observe: At a certain distance (usually around 10-12 inches), the 'O' will disappear. Continue moving closer, and it will reappear.
This disappearing act happens when the image of the 'O' falls precisely on your right eye's blind spot. Repeating the process with your left eye closed and focusing on the 'O' will make the 'X' disappear.
