What Causes A Brown Spot On The Left Eyelid After Chemotherapy?

I had four rounds of chemo last year for breast cancer. Had been experiencing dry eyes prior to treatment, but the chemo took the fluids from my eyes and caused extensive stippling of my corneas. We had to stop the chemo treatments because I lost sight in my left eye completely. Since then, my corneas have healed, but I still experience almost constant burning, stinging & dryness in my eyes. Have to use sterile drops during the day & ointment in my eyes at night. There seems to be nothing they can do for the pain. However, I did notice a brown spot that has appeared on my left eyelid over the course of the last few months. It had not been there before. Am assuming it is a pigmentation issue. . .what do you think??