The damage to the macula causes central vision to be distorted or destroyed. Vision loss may be rapid and severe. Straight lines may look wavy. The macula thins and dries out. The amount of vision loss is related to the location and the amount of macular thinning caused by the drusen.
Vision loss is gradual.
One way to test vision in order to detect even small changes when they first appear is to use the amsler grid. Sit in an area with good lighting and hold the chart at eye level at normal reading distance. Wear your reading glasses and hold the Amsler grid at a normal reading distance. Stare with your other eye at the central dot on the grid, observing the pattern of vertical and horizontal lines on the chart to be sure that all the lines are straight and all the small squares are the same size. Repeat the test with the other eye.