I am glad that you are aware of this diagnoses. If you really have pigmentary demarcated lines, then you will subtle areas of pigmentation mostly around the corners of your eyes in a V PATTERN. You must have experienced it during your teenage and now it persists.
Next Steps
There are really 2 things you can do.
Sit back and worry that its not improving and recurring even after treatment
or
you can understand that this is your skin type, there is no permanent cure and I have to continue taking medical treatments if I want to continue seeing results
Health Tips
Glycolic acid based combination creams works. Q switch laser gives beautiful results and so does spotless peels. Cosmelan or any other peel won't give permanent results. it is bound to recur if no maintenance is done