This is a grid that shows distorted central vision.
The central retina is at risk due to central serous edema, choroidal neovasculariztion for those with high myopia (over -6.00DS), and edema for those with diabetes during the age 30-50. For the older population, age related macular degeneration affects the central retina as well.
Watch this animation to see how one might see with this grid if they have age related macular degeneration here.
Click here for a printable Amsler Grid for home monitoring.