Sometimes an easy and straight-forward subjective refraction suddenly becomes difficult and the patient says what used to be clear is now blurry. Adding plus or minus doesn’t seem to clear it up. Why did the refraction become so foggy all of a sudden?
The patient could be fogging up the lenses on the phoropter. Have the patient sit back and take a look through the lenses. Commonly a suddenly-gone-wrong refraction will be due to fogging of the lenses, causing overall blur regardless of power. Wipe it up with a cleaning cloth, and now you can smoothly finish up your refraction.