Your physician may be right.   Eye stinging/burning/redness and temporary blurred vision are all side effects of pre forte. But your instincts are right, if any of those side effects persist or worsen, tell your doctor or pharmacist right away. Also look for any changes in the symptoms, such as pain (that wasn't there before she started the medication), dizziness, headache, runny nose, signs of an allergic reaction or any yellow or green discharge, which might indicate an infection. There may not be any cause for worry if you talked to your doctor about your concerns. As long as you feel like your concerns are being taken seriously and the doctor is willing to work with you, you mother-in-law should be fine.