What Is the Axis of Astigmatism in My Prescription?
- BY Catherine Ong
- IN Eye Health
Astigmatism is a common refractive error that occurs when the cornea or lens of the eye has an irregular shape. This causes light to focus unevenly on the retina. One essential aspect of diagnosing and correcting astigmatism is understanding the axis, which denotes the orientation, or rotation, of the irregular curvature. Don’t worry, though, because having astigmatism is a common refractive error and can often be resolved with a pair of prescription lenses.
Mechanism and Effects of Astigmatism and Axis
In astigmatism, the cornea and/or lens are shaped more like a spoon or football shaped rather than a sphere, resulting in two different curvatures typically 90 degrees apart. Imagine our eyeball like a globe with longitude and latitude – an eye with astigmatism will have different curves in its equator versus Prime Meridian resulting in an irregular shape. This uneven curvature causes light rays to focus on multiple points in front or behind the retina, rather than a single point on the retina. As a result, individuals with astigmatism often experience blurred or distorted vision at various distances.
Photo by Jean-Daniel Francoeur
Notation
There are two parts of your prescription that are needed to describe astigmatism: cylinder and axis.
- Cylinder (“Cyl”): The cylinder (“cyl”) number will denote the magnitude of astigmatism. The larger the number, the larger the difference between one meridian and the meridian perpendicular to it.
- Axis: The axis of astigmatism refers to the orientation of the most curved meridian, ranging from 0 to 180 degrees.
- You cannot have a cylinder without an axis, and likewise you cannot have an axis without a cylinder.
- If you do not have astigmatism, you are considered a sphere (where all meridians are of equal curvature), and thus your cylinder number would be 0.00 (zero).
Symptoms of Improper Axis
So what happens if there are errors in your axis?
- Headaches: Astigmatism can cause eye strain and headaches, especially after prolonged periods of visual tasks.
- Blurred Vision: Objects may appear blurry or out of focus, particularly at certain distances.
- Warped Images: Straight lines may appear wavy or distorted, affecting perception.
- Eye Fatigue: Constant squinting or straining to see clearly can lead to eye fatigue and discomfort.
Common Causes of Misaligned Axis
- Misaligned Glasses: Glasses that are not properly aligned or are skewed on the face can alter the axis of astigmatism.
- Round Lenses with Lens Rotation: Glasses with round lenses are more prone to rotate within the frame. Over time, your lenses may rotate out of place and cause blurred vision or headaches.
- Incorrect Prescription: An outdated or incorrect prescription can result in improper correction of astigmatism.
- Sitting with Head Crooked During Vision Test: Poor positioning behind the phoropter during an eye examination can lead to inaccurate measurements of astigmatism axis. Make sure you are sitting straight and facing forward without any head tilt.
- Adaptation: Sometimes, it is difficult for our eyes to adjust to even small changes in astigmatism even if it can make our vision clearer. For those who are more sensitive to changes in prescription, make sure you let your optometrist know so they can help balance visual clarity with visual comfort.
Understanding the axis of astigmatism is crucial for accurate diagnosis and correction. If you experience symptoms listed above or notice changes in your vision, it’s essential to schedule a comprehensive eye examination with an optometrist. Once you have your updated prescription, shop glasses that are perfect for your face shape to ensure the optimal fit. With the right corrective measures, such as prescription glasses or contact lenses, individuals with astigmatism can achieve clear and comfortable vision.
