Please note: this article is for information only. Astigmatism can only be diagnosed, and your prescription determined, by an optometrist or an ophthalmologist. If you notice changes in your vision, book an eye examination.
Do your eyes tire easily when you read or drive? Do letters look slightly blurred or “stretched”, or do car headlights seem to have rays and starbursts at night? You may have astigmatism. It is one of the most common vision problems, and it happens when the cornea or the lens inside the eye is not evenly curved, which distorts the image. In this guide we explain what astigmatism is, how to tell whether you have it, how to read the cylinder and axis on your prescription and which options exist to correct it.
Have astigmatism and want to update your glasses? At Lens4Glasses we replace the lenses in your own frame with your full prescription (sphere, cylinder and axis). Take a look at our single vision lenses, and if you also need help with close-up vision, our progressive lenses.
What is astigmatism?
Astigmatism is a refractive error: the eye does not focus light on a single point on the retina. In an eye without astigmatism, the cornea is curved roughly the same way in every direction, like a football. In an eye with astigmatism it is shaped more like a rugby ball: more steeply curved in one direction than in the other. As a result, light is focused at two different points and the image looks blurred or distorted, both far away and up close.
Astigmatism is very common and often appears together with short-sightedness (myopia) or long-sightedness (hyperopia). In fact, many glasses prescriptions include at least a small amount of it.
Types of astigmatism
- Regular astigmatism: the most common type. The directions of strongest and weakest curvature are at right angles to each other, and it is corrected well with glasses or contact lenses.
- Irregular astigmatism: the surface of the cornea is uneven, for example because of scarring, injury, previous surgery or conditions such as keratoconus. It usually needs a specific assessment by a specialist and sometimes special contact lenses.
Do I have astigmatism? How it is diagnosed
The only reliable way to find out is a full eye examination with an optometrist or an ophthalmologist. You will be asked to read letters or numbers at a set distance, and your visual acuity will be measured with and without correction.
The eye care professional may also use several instruments:
- Autorefractor: gives a first measurement of your prescription, including astigmatism.
- Keratometer: measures the curvature of the cornea.
- Corneal topographer: creates a detailed map of the corneal surface and helps detect irregular astigmatism.
- Subjective refraction: the familiar “better with this one or this one?” test, used to fine-tune the cylinder and the axis.
- Ophthalmoscope: lets the examiner look inside the eye and at the retina to rule out other problems.
Regular eye tests are recommended even if you have no symptoms, and especially for children, because uncorrected astigmatism can affect how their vision develops.
Symptoms of astigmatism
If you have astigmatism, you may notice some of these symptoms:
- Blurred or distorted vision at any distance, far or near.
- Eye strain or headaches after reading, driving or working on screens.
- A feeling that letters or objects have shadows or look doubled.
- Squinting to try to see more clearly.
- Poorer vision at night, with halos and glare around lights.
How strong the symptoms are depends on the amount of astigmatism. With a small amount you may not notice anything; with more, blur and eye strain become more obvious.
Distorted rays of light are one of the most typical signs. Because light is not focused on one precise point on the retina but on several, light sources appear to have rays, reflections or starbursts coming out of them. Someone without astigmatism sees street lights as clean points of light, while someone with astigmatism may see streaks of light coming out of each one.
How to read the cylinder and axis on your prescription
If you have astigmatism, your prescription will show three values for each eye instead of one. Here is an example:
| Eye | SPH (sphere) | CYL (cylinder) | AXIS |
|---|---|---|---|
| OD / R (right eye) | -1.50 | -0.75 | 180° |
| OS / L (left eye) | -2.00 | -1.25 | 10° |
- OD and OS (or R and L): right eye and left eye.
- SPH (sphere): short-sightedness (minus sign) or long-sightedness (plus sign), in dioptres.
- CYL (cylinder): the amount of astigmatism, also in dioptres. If the box is empty or shows 0 (sometimes written “DS” or “sph”), that eye has no astigmatism to correct.
- AXIS: the orientation of the astigmatism, an angle between 0° and 180°. It does not describe how much astigmatism you have, only its direction: 180° and 0° are the same position (horizontal) and 90° is vertical. Without the axis, the cylinder cannot be made.
About the sign of the cylinder: many optometrists write the cylinder as a minus value, but some use plus values. Both forms can describe exactly the same prescription, simply written in a different way (when converting from one to the other, the sphere and the axis change too). That is why it is important to copy your prescription exactly as written, signs included, and never mix values from different prescriptions. If in doubt, ask the professional who tested your eyes.
When you order your lenses, enter the three values for each eye exactly as they appear. A mistake in the axis, even of a few degrees, can noticeably reduce the quality of your vision when the astigmatism is high.
How much astigmatism is a lot?
As a rough guide, these ranges are commonly used for the cylinder value:
- Up to 0.75 D: mild astigmatism. Many people barely notice it, although correcting it can improve sharpness and comfort.
- From 1.00 to 2.00 D: moderate astigmatism. Blur and eye strain are usually noticeable if it is not corrected.
- Over 2.00 D: high astigmatism. Correction is important for clear vision, and regular follow-up with a specialist is advisable.
These figures are only a guide. What really matters is how astigmatism affects your vision and your daily life, and that is something your optometrist or ophthalmologist will assess, deciding whether and how it should be corrected.
Astigmatism and night driving
Many people first notice their astigmatism behind the wheel. At night the pupil widens and light enters through a larger area of the eye, so focusing errors become more noticeable. The result is halos around headlights, star-shaped flares from street lights and traffic lights, and more glare overall.
To drive more comfortably at night:
- Always wear an up-to-date prescription with the correct cylinder and axis. Uncorrected or poorly corrected astigmatism makes halos worse.
- Choose lenses with an anti-reflective coating: it reduces reflections on the lens surface and helps you see with better contrast.
- If your night vision is still much worse even with your prescription, see an eye care professional: there are other causes worth checking.
How can astigmatism be corrected?
There are several ways to correct astigmatism:
- Glasses: the simplest and most common option. Lenses for astigmatism have a different power in each direction (which is why they are called toric lenses) and are fitted in the frame at the angle given by your axis, compensating for the uneven curvature of the eye.
- Toric contact lenses: contact lenses designed for astigmatism that keep their orientation on the eye. Irregular astigmatism may require rigid or specialist lenses. Contact lenses should always be fitted by a professional.
- Refractive surgery: techniques such as LASIK or PRK reshape the cornea, and in some cases toric intraocular lenses are used. Not everyone is a suitable candidate: an ophthalmologist assesses each case, including the benefits and the risks.
Talk to your optometrist or ophthalmologist about the most suitable option for you, taking into account your degree of astigmatism, your age, your lifestyle and any other eye conditions.
Which lenses to choose if you have astigmatism
If you only need to see clearly at one distance (or you are under about 40 and can still focus well up close), the usual choice is single vision lenses made with your sphere, cylinder and axis. Astigmatism does not require a special kind of lens: it is simply part of the prescription that is surfaced into the lens.
To choose the lens index (how thin the lens will be), looking at the sphere alone is not enough. What counts is the strongest meridian, which you get by adding the sphere and the cylinder, signs included. For example, with a sphere of -2.00 and a cylinder of -2.50, the strongest meridian is -4.50, and the edge of the lens will be thicker in that direction. As a general guide:
- Low prescriptions (up to about 2 dioptres in the strongest meridian): a 1.5 or 1.6 index is usually enough.
- Medium prescriptions (from about 2 to 4 dioptres): a 1.6 or 1.67 index improves thickness and appearance.
- High prescriptions (over about 4 or 5 dioptres): it is worth considering 1.67 or 1.74.
If your prescription is high, our article on thinner lenses for high prescriptions (index 1.67 vs 1.74) explains the differences between indices. And if you prefer a leading brand, we also offer ZEISS single vision lenses.
If you also have presbyopia and want to see both far and near with the same pair of glasses, the answer is progressive lenses, which also include your cylinder and axis.
Frequently asked questions about astigmatism
Is astigmatism hereditary?
It has a strong genetic component: many people are born with some astigmatism, and it often runs in families. It can also appear or change because of injuries, surgery or diseases of the cornea. That is why children should have their eyes tested even if they do not complain.
Does astigmatism get worse with age?
In most adults it is fairly stable, although it can change slightly over the years, especially the axis. A rapid increase in astigmatism, particularly in young people, should be checked by an ophthalmologist, as it can be linked to conditions such as keratoconus.
Can you have astigmatism in only one eye?
Yes. It is quite common for one eye to have astigmatism and the other not, or for each eye to have a different value and axis. That is why prescriptions give the values for each eye separately.
Which is better for astigmatism, contact lenses or glasses?
Both correct astigmatism. Glasses are easier to use and do not touch the eye; toric contact lenses give a full field of view and are practical for sport. Many people use both. Contact lenses should be fitted by a professional.
Does astigmatism make lenses more expensive?
The price of lenses depends mainly on the type of lens (single vision or progressive), the index you choose and any coatings or filters you add. You can see the exact price for your prescription in the configurator on each product page before you order.
Can I have astigmatism lenses fitted in my current frame?
Yes, in most frames that are in good condition. We fit the lenses at the angle given by your axis so that the correction sits in exactly the right position.
Conclusion
Astigmatism occurs when the cornea or the lens is unevenly curved and light is not focused on a single point on the retina, causing blurred or distorted vision, eye strain and halos at night. It is very common and, in most cases, is corrected well with glasses or contact lenses. The key is a full eye examination with an optometrist or ophthalmologist, keeping your prescription up to date and choosing lenses with the right index for your strongest meridian.
Ready to update your glasses? Lens4Glasses replaces the lenses in your own frame with your full prescription, including cylinder and axis: choose our single vision lenses or, if you also need reading vision, our progressive lenses.