Our visual perception isn’t flawless. A blind spot refers to an area within your field of vision where no light detection occurs. This phenomenon is a normal part of how our eyes are structured, and everyone experiences it. We are unaware of these areas, as the brain compensates for the missing information.
The Normal Physiological Blind Spot
Every human eye possesses a physiological blind spot. This area exists because of the optic disc, the point where the optic nerve exits the back of the eye and connects to the brain.
This region lacks photoreceptor cells—rods and cones—responsible for detecting light and sending signals to the brain. Consequently, light falling directly onto this spot cannot be perceived.
Despite this inherent gap in our vision, we rarely notice it in our daily lives. The brain employs a process called “filling-in” or “perceptual completion” to compensate for this missing visual data.
It interpolates the missing information, using surrounding visual cues and data from the other eye to construct a complete image. This means the blind spot doesn’t appear as a dark patch or a hole; rather, the brain seamlessly predicts and fills the area with what it expects to see, based on the surrounding patterns and colors. For instance, if you are looking at a striped pattern, the brain will extend the stripes through the blind spot, making it seem as though the pattern is continuous.
Pathological Blind Spots and Their Appearance
Beyond the normal physiological blind spot, abnormal blind spots, known as scotomas, indicate an underlying health condition. Unlike the unnoticed physiological blind spot, these are often perceived and vary in appearance and impact on vision, manifesting as dark or blurry patches where vision is diminished or entirely absent.
Some pathological blind spots appear as shimmering or flickering lights, characteristic of migraine auras, known as scintillating scotomas. These can start as a small, bright area and expand, sometimes covering a large portion of the visual field before a migraine headache begins.
Other scotomas can present as areas where certain colors cannot be seen, or vision is only possible in very bright light. These abnormal blind spots can be caused by various conditions affecting the retina, optic nerve, or even the brain, including glaucoma, macular degeneration, strokes, or multiple sclerosis.
Identifying a Blind Spot
You can locate your physiological blind spot with a simple test. Close one eye, then focus the open eye on a specific dot or small object placed directly in front of you.
While maintaining your gaze, slowly move another small object, such as your thumb, from the periphery of your vision towards the center. At a certain point, the object will temporarily disappear from your sight as its image falls directly onto your optic disc. Continuing to move the object will cause it to reappear, confirming the location of your blind spot.
Pathological blind spots, however, may be noticed differently in daily life. You might observe missing words or sections when reading text, or find yourself bumping into objects on one side due to a gap in your peripheral vision.
These occurrences suggest an area of vision loss that the brain is not effectively compensating for. Any new or unusual visual disturbance should prompt further investigation.
When to Seek Medical Attention
Seek prompt medical evaluation if you experience any new or changing blind spots in your vision. A sudden onset of a blind spot, or one that rapidly interferes with daily activities, warrants immediate attention from an eye care professional, especially if it is persistent, growing in size, or associated with other symptoms.
Additional warning signs that require medical consultation include blind spots accompanied by eye pain, flashes of light, or an increase in floaters, which are small specks or strands that drift across your vision. These symptoms could indicate serious underlying conditions that require timely diagnosis and treatment to prevent further vision loss.
Regular eye examinations are also recommended to detect potential issues early.