The macula is that part of the retina that serves the central vision. When you are looking directly at an object, you are projecting the image of that object on your macula.
Macular edema is swelling of the macula.
Hydrochlorothiazide is a drug used for treating high blood pressure.
This paper discusses the case of a gentleman who developed macular edema after initiation of therapy with hydrochlorothiazide.