Why do I see squiggly lines with bright light in my eye?

Patients often notice that lights during an eye exam are really bright. Sometimes, people notice a pattern of lines that they only see with bright lights shining in their eyes. This pattern of squiggly lines is always the same, but these people don’t notice the lines when there aren’t any bright lights. What are they? Some astute patients say, “I can see the blood vessels in my eye!” Indeed the lines are areas where blood vessels travel in the retina, so we don’t perceive light in those spots the same way we do in other parts of the retina. The same thing is true for the optic nerve head, which represents the site of the “normal blind spot.” Since the blood vessels are always in the same spot, it wouldn’t help us to notice them all the time, so our brain “tunes out” the blood vessels. That’s why we can’t normally see them! Sometimes, patients who have one or two floaters eventually start to “tune out” the floaters as well to some extent. We are lucky that our brains adapt to help us see what we really want to see rather than keeping input data that we might not need.

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