Autoperimetry

A perimetry test (visual field test) measures all areas of your eyesight, including your side, or peripheral, vision.
To do the test, you sit and look inside a bowl-shaped instrument called a perimeter. While you stare at the centre of the bowl, lights flash. You press a button each time you see a flash. A computer records the spot of each flash and if you pressed the button when the light flashed in that spot.
At the end of the test, a printout shows if there are areas of your vision where you did not see the flashes of light. These are areas of vision loss. Loss of peripheral vision is often an early sign of glaucoma.