What Treatment Should I Take For Blackened Vision In The Left Eye ?

Hello, my left eye fades to a inverted sort of color, which is just the right part of vision that I can barely make anything out. My left eye has been doing this for maybe about two or so years, but it wasn t until recently that I wanted to find out what was causing this. My left eye has been a major part in much of my vision, like not being able to read without it being a pain or see many things far away. My right eye on the other hand is perfectly fine and is probably my more dominant eye. For much of this time, I never thought anything of it and thought about doing nothing considering it only lasts for short periods of time.