Visual Acuity

Snellen Chart


Visual Acuity


Some of the medications used to treat nontuberculous mycobacterial infections can cause vision changes, and it is essential that you and your doctor monitor for these changes. Monitoring should include visual acuity (particularly when using ethambutol or rifabutin), and red-green color discrimination (ethambutol). In addition to regular vision checks by a qualified ophthalmologist, you can also perform regular checks of your vision at home.


Visual acuity testing is often done using a Snellen eye chart, which is printed with multiple lines of block letters decreasing in size. It is imperative to have regular vision checks, but if you want to monitor your vision in between checkups, you can download and print a Snellen chart and instructions here.


There are also other visual acuity tests you can perform on your own at


You can also monitor your visual color discrimination (especially red-green color blindness) by using an Ishihara test, which makes images with numbers out of dots that are a different color than the dots surrounding them and then asks you to determine what number is in the picture. There are several online sites to do color blindness tests. You should try to do the tests from the same device, in the same room with similar lighting every time. If you notice any changes, contact your doctor right away.


This website has several color blindness tests you can do:


This site offers a simple 12-plate Ishihara test:


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