That is correct. Print out and do off paper. One eye at a time. Pathology shows up right away . You can google abnormal amsler grids to see what they look like.
Don't have an answer for you, but will say, my doctor said not to do the amsler grid test on a computer screen. He said to print it out and then you can use a pencil to mark / draw any anomalies and show it to him. I am nearsighted with floaters. It seems like every time I look at it I get somewhat different result - nothing dramatic and I can tell the floaters affect it. Dr examined me though and said all good. I look at it for like 10 seconds each eye. Take care, Jim