What is the reason for worsening eyesight?

My eyesight worsens in the evening. Sometimes my eyes feel gritty and blurry as if dust is in front of them, and I have to blink briefly to clear the sensation and see clearly. Why does this happen? I have diabetes and undergo comprehensive eye exams every six months. They mentioned that I have some early-stage cataracts. Could these symptoms be caused by the cataracts?