Last Update: 12/10/2000

Here is a test pattern that is sometimes used to test for astigmatism in an eye exam.  A person with no astigmatism would see all the lines in focus, and the same darkness.  A person with astigmatism would see one of the sets of lines as darker and more in focus than the other sets of lines.

When you look through a cylinder lens with a power of -6.00, and hold it at an axis of 180, this is what you would see.  If this was your actual eyesight (-0.00 x -6.00 x 180), you would need glasses that were the opposite of this power.  The glasses would have a power of  -0.00 x +6.00 x 180, or +6.00 x -6.00 x 090.  Notice how the vertical lines are the same width apart (with and without the lens), but the horizontal lines are smaller and closer together.  This shows that all of the power (-6.00) of the lens is on the 180 axis, and no power is on the 90 axis.

This lens is -0.00 x -6.00 x 135.  Notice how the diagonal lines are the ones in focus now.  Also, notice the distortion you get when the axis is at 135.

Here is a plus cylinder lens.  The power is -0.00 x +6.00 x 180.  Notice how the vertical lines are normal size, and the horizontal lines are much bigger and further apart.  This is from the +6.00 cylinder power at axis 180.  If this were your actual vision, you would need glasses with a correction of -0.00 x -6.00 x 180, or -6.00 x +6.00 x 90.

This is the same lens, but with an axis of 90.  Notice the width of the lines has switched from the picture above.