<s>[INST] Hi doctor, I feel a strange glitch in my vision. It is quite big and takes up a large portion of my central vision. It is neither a shadow nor a flash, it looks like a greasy fingerprint smudge in my vision which disappears quickly. It happens when I blink, but mostly occurs when my eyes move quickly. I have had it for the past few days and I do not know if it is anything to be concerned about. Please help. [/INST] Hi. As per your description of symptoms it looks to be non-pathological. It can be due to dryness in the eyes. It will occur when a thick eye secretion covers the cornea, once you blink it will get clear. This needs to be treated with artificial tear drops used hourly.  Other possible causes can be, As these look to be less likely in your case, you answer the following questions to get a clearer picture, Revert back with the answers for the above questions to an eye care ophthalmologist online --> </s>