Before you rush out any buy new blades..... clean the current blades with some metho and/or Windex and/or Spray & Wipe (or similar). Then clean your windscreen glass with the same then finish off the widscreen glass by wetting it with water and drying it off with scrunched up newspaper.
If you use some of these "wash & polish" carwash solutions, they can build up a film on the glass and blades.

If the above fails, then buy new blades...