Understanding the Axis in Contact Lenses: What It Means and Why It’s Important

May 26, 2024 Ofelia Braun Contact Lenses Beginner 0

istockphoto-1307872617-612x612 — Medical eyeglass prescription with parameters, glases and contact lens container on yellow background

Reading your contact lens prescriptions can be overwhelming. It demands that you know and understand some terms and abbreviations. One such is the axis always accompanied by a figure.

Seeing an axis value of 100 or 75 on your contact lens prescription can raise questions and worries. However, you don’t need to fret. We will reveal everything you need to know about an axis in contact lenses – meaning and importance.

What does the Axis in Contact Lenses Mean?

Now to the big question – what does an axis mean in a contact lens prescription?

The axis is associated with astigmatism. It tells your eye care professional direction to position the cylindrical power in your lenses. In astigmatism, the cornea or lens of your eye has an irregular shape that leads to blurry or distorted vision. The axis works to correct the irregular shape.

Put it this way – axis means the value in degrees between the meridians of your astigmatic eye.

The Role of the Axis in Correcting Vision

Axis is not just peculiar to contact lenses; you can also find it in a glasses prescription. The axis number ranging from 1 to 180 degrees indicates direction. 90 indicates a vertical position, while 180 indicates a horizontal meridian.

The axis value is very crucial in astigmatism correction. Its value comes from the fact that it indicates the orientation of the cylindrical lens needed to counteract the irregular shape of the eye.

How is the Axis Measured?

Your eye doctor must perform an eye test to determine your axis number. One notable instrument is the phoropter, which has multiple lenses that you wear to look through while reading a chart. Your eye doctor keeps adjusting the lens and asking for feedback until you have clearer vision. There are some other tests involved.

Remember, your axis number shows the direction of your astigmatism. You may ask for the figure that represents a normal eye axis. If you have ‘normal’ eyesight, you won’t have an axis figure – no astigmatism. Being without astigmatism means that light falls in the correct place on the retina. Therefore, the eyes closest to a normal eye with astigmatism usually have a reading of 0.50 dioptres of negative cylinder power with a 180-axis number.

Why is the Axis Important in Contact Lenses?

Figures for cylinder and axis are only present when there is a need for astigmatism correction and toric lenses. Identifying and addressing the axis in your contact lens prescription helps ensure accuracy in vision correction. Neglect of the axis could result in blurry vision.

The axis in your contact lens or glasses prescription exists to correct astigmatism. Therefore, axis measurements in your eye prescription ensure that your lenses are tailored to your specific needs for vision correction.

Where to Find Axis on Contact Lens Prescription

Your contact lens prescriptions always contain several elements. These elements are listed for each eye separately (OD for the right eye and OS for the left eye). Some of these elements include:

Base Curve
Diameter
Sphere power for long or short-sightedness
Cylinder power
Axis
Contact lens brand
Add – for multifocal lenses.
Search for the section with the element AX or AXIS on your contact lens prescription. You’ll usually find it near the cylinder power value. Then, check the numerical value attached to it ( 0 to 180).
Consult your eye care professional, if you can’t find the axis on your prescription. However, you won’t find an axis in an eyeglass prescription.

Common Misconceptions about the Axis

Understanding your axis in an eye prescription can bring in a lot of confusion. Some of these confusions have led to several misconceptions.

Axis value has a plus or minus sign.

Axis measures in degrees from 0 to 180 with no minus or plus sign attached.

Some think that your axis value determines your overall eye health.

Know that your axis measurements don’t give any information about your eye health. To determine the former, you need a comprehensive eye test.

Your axis has no bearing on your corrective lens.

What the axis does is tell the direction of the cylindrical correction. For example, an axis of 90 means that the cyl power (cylindrical power) must be applied in a vertical meridian.

The axis is the same for both eyes.

You can have different values in each eye.

Axis measurement is related to pupillary distance.

Your pupillary distance and axis measurements have no relationship. Your pupillary distance is the distance between the centers of your pupils.

Vertex Distance affects axis measurement.

This is the distance between the back of your corrective lenses and the front of the eyes. While vertex distance can affect high-powered spherical and cylindrical prescriptions, it doesn’t for axis measurement.

The axis value indicates the greatest and weakest powers in the lens. Cylinder power indicates them, not the axis.

Choosing the Right Contact Lenses for Your Axis

Here are a few pointers to choosing the right contact lenses for your axis:

1. Ensure that your eye prescription has the accurate and correct measurements for your axis and cylinder. Only a comprehensive eye test will give the correct figures.

2. When choosing lenses, select the ones with the exact power for your astigmatism.

3. Don’t forget regular check-ups to ensure your lenses remain effective.