Can lack of exercise lead to blindedness or poorer eyesight?

Not by itself: Lack of exercise alone would not cause eyesight to become poor, but if your diet is also poor then there are some vitamin deficiencies that can lead to things like night blindness. High blood pressure and some other diseases could cause your eyesight to change for the worse. You're best off having it checked out, because it may be a sign of a serious health issue!