I've got one. It was detected by my Optician during a routine eye test .I was referred for further tests as a precaution. I had no symptoms noticeable to myself. The check procedure consists of an eye examination and a scan to determine the size & thickness of the mark. The consultant inspects these results and usually asks for a return visit in 6 months. The scan results are compared and any changes noted. In my case the mark was described to me as fuzzy edged ,thin and stable and pronounced harmless by the consultant. From what I gathered during my visits this is the most common result by far. My experience was in the UK NHS system. First class all round. Procedures could differ elsewhere.