Hi, I Have Noticed Several Times Over The Last Month

Hi, I have noticed several times over the last month or so a vertical darkening/line in my lower eyelid. It always seems to be when I have a feeling something is in my eye and I'm going to use Visine. I never seem to remember to look at other times but it is starting to concern me as it is a dark line. I've never noticed it before when looking, just over the last month or two, about 3 or 4 times. I can't seem to find anything online about it. Could it be allergy related? Medication related? Should I have it checked out?