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Axis is the orientation of the cylinder portion of your lens [prescription], used to compensate for astigmatism. You don't have an axis value if you don't have astigmatism. From the lens wearer's perspective, 0 degrees of axis is horizontal, and increasing values move clockwise around the eye. The axis of cylinder is symmetrical, so it only goes from 0 to 180 degrees.

Axis of astigmatism can be measured with a stenopaeic slit or JCC lens but the use of these tools is complex and easily misunderstood, it's usually best to get your axis off of your most recent prescription.