Experiencing brief visual perceptions in the corner of your eye, which disappear when you turn to look directly at them, is a common phenomenon and usually nothing to be concerned about. There are several possible reasons for this:
Peripheral vision: The peripheral vision is not as sharp or detailed as the central vision. It is more sensitive to motion and changes in light and contrast. As a result, you may catch movements or fleeting shadows in your peripheral vision that your central vision fails to confirm when you turn to look directly at them.
Eye floaters: These are tiny, semi-transparent specks or strands that float in the vitreous fluid inside your eyeballs. They can cast shadows on your retina and be perceived as moving objects in your peripheral vision.
Phosphenes: Phosphenes are the sensations of seeing flashes of light or colored spots without any external light source. They can be caused by mechanical pressure on the eye, such as rubbing your eyes, or by stimulation of the retina by electrical signals, like when you stand up too quickly.
Visual processing delay: Sometimes, your brain may take a moment to process visual information accurately, especially when there are sudden changes or movements in your environment. This can lead to momentary misinterpretations of what you see in your peripheral vision.
Attentional bias: Your brain is designed to prioritize certain stimuli over others based on your focus and attention. In some cases, you may be more prone to noticing or being sensitive to movements or changes in your peripheral vision due to a heightened state of awareness or anxiety.
Unless these visual perceptions significantly impact your daily life or are accompanied by other concerning symptoms, such as flashes of light, floaters, or vision loss, they are typically considered normal and not a cause for alarm. However, if you have any persistent visual disturbances or concerns about your vision, it's always a good idea to consult an eye care professional for a thorough evaluation.