Working out can cause some of your senses to numb as the intensity of exercise saps your mind's focus. But the development of blurry vision may be a concern all of its own.

Exercise stresses the body -- stress is what causes the positive results -- but exercise should not cause frightening symptoms like dizziness or loss of vision. When you experience negative symptoms like these, it is your body's way of telling you that something is wrong.

Pencil pushups are a workout for convergence insufficiency, or hand-eye coordination problems. A study performed by the Pennsylvania College of Optometry and published in "Optometry and Vision Science"