Cylindrical power, often abbreviated as ‘CYL’, is the part of an eye prescription that corrects for astigmatism. Astigmatism is a common refractive error where the eye’s cornea (the clear front surface) or the lens inside the eye is shaped more like a football (oval) than a basketball (spherical). This irregular shape prevents light from focusing correctly onto the retina, causing vision to be blurry or distorted at all distances.
The Concept of Astigmatism
To understand cylindrical power, you must first understand astigmatism. Imagine a perfectly round eye. It focuses light onto a single point on the retina, creating a sharp image.
In an eye with astigmatism, the cornea is curved more in one direction than the other. This causes light to focus on multiple points instead of one. As a result, a person with astigmatism might see a point of light as a stretched-out line, and their vision will be blurry for both near and distant objects.
Cylindrical power is the specific lens power required to correct this irregularity and bring the light back to a single focal point.
How to Read Cylindrical Power on Your Prescription
An eye prescription has three main components: Sphere (SPH), Cylinder (CYL), and Axis.
| Component | Abbreviation | What it Corrects | How it’s Written |
|---|---|---|---|
| Spherical Power | SPH | Corrects for nearsightedness (myopia, indicated by a minus sign) or farsightedness (hyperopia, indicated by a plus sign). | e.g., -2.50 D or +1.75 D |
| Cylindrical Power | CYL | Corrects for astigmatism. This value will only be present if you have astigmatism. | Written with a minus (-) or plus (+) sign, e.g., -1.25 D. |
| Axis | AXIS | Indicates the orientation or angle of the astigmatism, measured in degrees from 1 to 180. It is always present if there is a cylindrical power. | e.g., 180° or 090° |
Example Prescription:
OD (Right Eye): -2.50 / -1.25 x 180
- -2.50 (Sphere): This corrects for nearsightedness.
- -1.25 (Cylinder): This is the cylindrical power to correct for 1.25 diopters of astigmatism.
- 180 (Axis): This is the angle at which the astigmatism is located.
If the ‘CYL’ column on your prescription is blank or has ‘DS’ (Diopter Sphere), it means you do not have any significant astigmatism in that eye.
Symptoms of Astigmatism
If you have uncorrected astigmatism, you might experience:
- Blurry or distorted vision at all distances.
- Eyestrain and headaches, especially after reading or using a computer.
- Difficulty seeing at night.
- Squinting to try and see clearly.
How is Astigmatism Corrected?
Astigmatism is corrected with a cylindrical lens. This special lens has more power in one direction than the other. It is precisely crafted to counteract the irregular shape of your cornea or lens, thereby allowing light to focus correctly on your retina.
When you get glasses for astigmatism, the lab needs all three values—Sphere, Cylinder, and Axis—to make the correct lens. The axis tells the lab exactly how to orient the cylindrical power in the eyeglass frame.
Understanding your eye prescription is a key part of managing your eye health. It’s the first step to achieving clear vision, often referred to as 6/6 vision.
Frequently Asked Questions (FAQs)
What does cylindrical power in the eye mean?
Cylindrical power is the lens power in your eyeglass prescription that is needed to correct astigmatism. Astigmatism is a vision problem caused by an irregularly shaped cornea, which leads to blurry or distorted vision.
Is having cylindrical power normal?
Yes, having a small amount of cylindrical power is very common. Most people have some degree of astigmatism. It only needs to be corrected with glasses or contact lenses if it is significant enough to cause blurry vision or eyestrain.
What is the difference between spherical and cylindrical power?
Spherical power corrects for nearsightedness or farsightedness and is the same in all meridians of the eye. Cylindrical power corrects for astigmatism and is only applied in a specific direction (the axis) to compensate for the eye’s irregular shape.
Is a cylindrical power of -0.75 high?
No, a cylindrical power of -0.75 is considered a mild amount of astigmatism. It may or may not cause significant symptoms. Whether you need glasses for it would depend on your individual vision needs and your doctor’s recommendation.
Can cylindrical power be cured?
Astigmatism, the underlying cause of cylindrical power, cannot be ‘cured’ in the traditional sense, but it can be easily and effectively corrected with prescription eyeglasses, contact lenses, or through refractive surgeries like LASIK.