A cataract is a clouding of the lens of the eye. This is caused by aging of the eye and the buildup of proteins in the lens. The buildup of proteins is what causes the cloudiness of the eye, which then affects one's vision. Vision may not always be affected by a cataract, but most often a person with a cataract has blurry or dimmed vision.
Treatment for a cataract is not always necessary, especially if it is having a minimal impact to your vision. However, if your vision is significantly impacted and begins to interrupt you daily life, then it may be time to consider treatment options.