The seven Amsler grid charts
The grid most people know is Chart 1 of a set of seven. Here is what each chart looks like and why it exists.
Marc Amsler's original charts were white on black. The black-on-white grid handed out today is a later, easier-to-print version of Chart 1.
Which chart should I use at home?
Use Chart 1, in whichever colors your eye doctor gave you. It is the chart nearly all home instructions are written for. On the online test you can choose black on white, white on black or red on black, and add the diagonal lines of Chart 2. The printable grid offers the same choices on paper.
Charts 3 to 7 are mostly used by eye doctors during an exam. They answer more specific questions and are not needed for routine home checks.
The size of the grid
Every chart is 10 cm by 10 cm. On Chart 1 each square is 5 mm, which covers about 1 degree of vision when the chart is about 30 cm (12 inches) from the eye. The whole grid therefore covers about 20 degrees: 10 degrees to each side of the dot. That is the area served by the macula and a little beyond.
This is why size and distance matter. A grid drawn too small, or held too far away, checks a smaller part of your vision than it should.
White on black or black on white?
Amsler's originals were white on black. Black on white became common because it prints well on any printer. Some people find that distortions stand out more on the white-on-black grid, while others see no difference. Neither has been shown to be clearly better, so the best choice is the one you can see comfortably. What matters is using the same one each time.
Red, blue and yellow grids
A red grid was once used to screen people taking hydroxychloroquine (Plaquenil) for damage to the retina. The American Academy of Ophthalmology no longer recommends the Amsler grid for that purpose and advises visual field testing and retinal scans. Blue-and-yellow grids exist for use in clinics and are not part of Amsler's set.
Where the charts come from
Marc Amsler (1891 to 1968) was a Swiss ophthalmologist. He introduced the charts in the 1940s and published them in 1947 as a simple way to examine the central visual field. They have changed little since.
Questions about the charts
How big is a standard Amsler grid?
10 cm by 10 cm (about 4 inches), divided into 400 squares of 5 mm, 20 across and 20 down, with a dot in the center.
What are the diagonal lines for?
They help people who cannot see the center dot because of a central blind spot. You look at the place where the two diagonals seem to meet, which keeps your eye steady.
Is the red Amsler grid still used for Plaquenil screening?
Not as a recommended test. The American Academy of Ophthalmology dropped the Amsler grid from its hydroxychloroquine screening advice. If you take hydroxychloroquine, ask your eye doctor about the screening schedule you need.
Who invented the Amsler grid?
Marc Amsler, a Swiss ophthalmologist, who published the charts in 1947. Earlier doctors had used grids and parallel lines to study distorted vision, and Amsler turned the idea into a standard set.