The Amsler grid, used since 1945, is a grid of horizontal and vertical lines used to monitor a person's central visual field. It is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the macula (e.g. macular degeneration, Epiretinal membrane), as well as the optic nerve and the visual pathway to the brain.
An early diagnosis means early treatment, so it may help to limit or at least slow the vision loss you experience.
If you are at risk for macular degeneration or other eye diseases, you can use this chart at home to monitor your vision. But using the chart doesn't mean you should skip regular visits to your eye doctor, because you can easily miss signs that only a trained eye care practitioner will find.