Final answer:
The increased eyelash growth is a side effect of the eye drop medication used to treat glaucoma.
Step-by-step explanation:
The eye drop medication used to treat glaucoma causes an increase in eyelash growth, which is a side effect of the medication. A side effect is an unintended consequence of a drug or treatment that is not the primary purpose for which the drug was developed. In this case, the medication is primarily used to treat glaucoma, but it also has the side effect of stimulating eyelash growth.