I have been answering questions on this eye forum since 2007. There are literally scores of posts on this complaint and thousands of replies. There are literally scores and scores of causes of this problem. However if you have had several normal eye examinations, special testing, and over time nothing new or ominous has developed then I would stop worrying about it. All optical systems have imperfections called optical aberrations. In the eye they can arise from glasses, contact lens, the cornea, lens, vitreous, macula. Light fails to arrive at the retina in a single spot but a varying size spectra which causes the ghosting. Most people get used to it and ignore it. Some people, especially the anxious or hypochondriacal, fixate on it which only makes it worse.