Many people with cataracts or other ocular media opacities are disabled in bright light conditions, due to the intraocular scatter.  The BAT test is used to test glare disability in three common bright light conditions.  These three conditions consist of: 1) direct overhead sunlight 2) partly cloudy day 3) bright overhead commercial lighting.  The patient s vision can be measured using low, medium or high light settings on the BAT instrument.  The low lighting condition is similar to lighting in the workplace (driving, construction work, computer use, etc).  The strong high light sources replicate oncoming headlights or a bright sky surrounding a visual target.  If the patient s vision gets worse using the BAT, the patient is considered to have a glare disability.  Usually this is caused by a cataract.