Brown syndrome is a problem with a tendon that attaches to the eyeball. In Brown syndrome, this tendon can't move freely. This limits the eye's normal movement. Brown syndrome is a rare disorder. It is usually present at birth (congenital). In some cases, it's acquired later in life.
Convergence insufficiency (CI) is a problem with the way the eye moves. It makes it hard to focus on things nearby. When the eyes converge, it means they point inward (toward the midline) to focus on something close. With CI, the eyes have trouble doing this. One eye may turn out instead of looking inward. CI can cause blurred vision, double vision, and eyestrain.