BAT is used to test glare disability. The Brightness Acuity Tester can simulate three bright light conditions: 1) Direct overhead sunlight; 2) Partly cloudy day; 3) Bright overhead commercial lighting. The vision is measured using the low, medium or high light settings of the BAT. If the vision falls with light then the patient is deemed to have glare disability.
Conditions of glare and low lighting arise in the course of many workplace tasks (e.g., driving, construction work, computer use). Strong extraneous light sources such as oncoming headlights or a bright sky often surround a visual target, creating glare problems. In addition to the cataract causing glare, light scatter from airborne particles or irregularities on otherwise transparent surfaces, such as windows and spectacle lenses may also contribute to glare. The impact of glare depends on the demands of the visual task. For example, when looking at a person silhouetted against a window or a very bright sky, contrast reduction can make it difficult to discern features in the face. In driving, detecting pedestrians, the edge of the roadways or reading signs against a bright sky, sun, or headlights is likely to be difficult if ability to see in the presence of glare is impaired.