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The axis is a number on your eyeglass prescription that indicates the direction of your astigmatism. It is a necessary part of a prescription, but only for people who have astigmatism. The axis number tells the lens maker exactly where to place the astigmatism correction in your lenses.
read more about axis in an eye prescription ...An eye with astigmatism is shaped more like a football than a perfectly round basketball. Because of this shape, the eye needs a different power in one direction than it does in another. The "cylinder" is the amount of power needed to correct for this. The axis is the number from 1 to 180 that tells the lab the angle or direction of that football shape.
On your prescription, you will see columns for Sphere (SPH), Cylinder (CYL), and Axis. If you have a number in the CYL column, you will always have a number in the Axis column. For example, a prescription might read CYL -1.50 and AXIS 090. This means you have 1.50 diopters of astigmatism correction placed at a 90-degree angle.
The axis is a very precise measurement. It works together with the cylinder power to give you clear vision. The cylinder provides the "how much" of the astigmatism correction, and the axis provides the "where." If the axis is even a few degrees off in your glasses, your vision can be blurry and uncomfortable. It is a critical instruction for making your glasses correctly.
Because the axis is so precise, the lens must remain perfectly stationary in the frame. If you have a round frame and the lens becomes loose, it might rotate slightly. Even a rotation of just a few degrees off-axis can cause significant blurriness for someone with moderate astigmatism. This is why opticians carefully secure astigmatism lenses, particularly in circular frames where rotation is physically easier.
An axis number is only needed if you have astigmatism. If your friend does not have astigmatism, the cylinder and axis parts of their prescription will be blank.
Yes, the axis of your astigmatism can shift slightly over the years. This is one of the reasons why getting regular eye exams is important to keep your prescription up to date.
An axis of 180 degrees is a horizontal orientation. An axis of 90 degrees is a vertical orientation. Most people have an axis somewhere between these two numbers.
Your eye doctor determines your axis during your eye exam. If you ever get a new pair of glasses and the vision feels tilted, strange, or just not quite right, it is possible the axis was made incorrectly. You should return to your optician and have them check the glasses against your prescription.
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