Final answer:
Latanoprost, used to treat glaucoma, is known to cause pigmented conjunctival cysts, which are generally benign and don't require treatment unless they cause discomfort or interfere with vision.
Step-by-step explanation:
The drug that causes pigmented conjunctival cysts is a) Latanoprost. Latanoprost is a medication used in the treatment of glaucoma, and it is known to cause a variety of ocular side effects, one of which can include pigmentation changes leading to conjunctival cysts. These pigmented conjunctival cysts are typically benign and arise from the accumulation of the pigment in the conjunctiva. The cysts can be a cosmetic concern, but they are usually harmless and do not require treatment unless they cause discomfort or interfere with vision.