The test is done one eye at a time. Cover the other eye and view the astigmatism dial. Do all the lines appear equally dark? If so, you do not suffer from astigmatism. However, if some lines appear significantly darker than others, you have astigmatism.

Note
The danger of astigmatism.

Astigmatism is a condition where light rays entering the eyes are unevenly refracted and brought to separate points of focus. The most common cause for this is due to an oval-shape cornea.

The danger of astigmatism is when it goes undetected and uncorrected in the young child. As the young child's eye is still developing, the constantly blur focus caused by astigmatism will lead to the development of a lazy eye (amblyopia).

If astigmatism suddenly developes, it may mean the onset of a potentially blinding eye disorder affecting the cornea called keratoconus.