It is very common for short-sight, clinically known as myopia, and astigmatism to occur together in the same eye. In fact, most people who require a prescription for distance vision have at least a small degree of both refractive errors. While myopia is primarily related to the length of the eyeball, astigmatism is caused by an irregular curvature of the cornea or the internal lens. When these two conditions coexist, the eye struggles to focus light correctly on two different levels, leading to vision that is not only blurred in the distance but also distorted or “stretched.” In the United Kingdom, opticians routinely identify and correct these combined errors using specialised lenses that address both the spherical and cylindrical aspects of the patient’s vision.
What We’ll Discuss in This Article
- The physiological reasons why myopia and astigmatism often coexist.
- How a combined refractive error affects the quality of distance vision.
- Understanding the “Sphere” and “Cylinder” parts of a combined prescription.
- The best types of spectacle lenses for correcting both blur and distortion.
- Options for contact lens wearers with combined short-sight and astigmatism.
- When to consider permanent surgical options for combined refractive issues.
The Biological Link Between Myopia and Astigmatism
To understand why these two conditions often appear together, it is helpful to look at the overall shape of the eye. Myopia typically occurs when the eyeball grows too long from front to back. As the eyeball elongates, it is not uncommon for the cornea the clear front window to also develop an asymmetrical shape. Instead of being perfectly round like a football, the cornea may become more oval, like a rugby ball. This asymmetrical growth pattern means that as the eye becomes more short-sighted, it frequently develops astigmatism as well.
Because the eye is one integrated biological system, the factors that influence the length of the eye often also affect the curvature of its surfaces. Genetics play a major role here; if you have a family history of high myopia, you are also more likely to have significant astigmatism. Short-sightedness is a very common eye condition that causes distant objects to appear blurred while close objects can be seen clearly, and it frequently occurs alongside other refractive issues. When these two errors combine, the eye’s focusing system is “mismatched” on multiple planes, requiring a more complex lens to bring everything back into a single, sharp focus on the retina.
How Combined Errors Distort Your Vision
When you have only myopia, distant objects look fuzzy but usually retain their basic shape. However, when astigmatism is added to the mix, those distant objects look both fuzzy and distorted. For example, a round clock on a distant wall might look like an upright oval, or the letters on a road sign might appear to have “ghost images” or “shadows” around them. This is because the short-sightedness is placing the image in front of the retina, while the astigmatism is causing the image to be focused at two different points rather than one.
This combined distortion can be particularly troublesome at night. Many people with both myopia and astigmatism notice that streetlights and car headlights appear to have long “streaks” or “tails” radiating from them. This is because the eye cannot find a single point of focus for the incoming light. The brain has to work much harder to try and make sense of these distorted signals, which often leads to significant eye strain, forehead tension, and headaches by the end of a busy day. Correcting both parts of the error is essential for achieving true visual comfort.
Reading Your Combined Prescription
If you have both short-sight and astigmatism, your spectacle prescription will contain several different numbers. The “Sphere” (SPH) value represents the amount of myopia you have. This will be a negative number, such as -3.00, indicating that your eye is too long or too powerful. The “Cylinder” (CYL) value represents the amount of astigmatism, which is the difference in power between the two different curvatures of your eye. Finally, there will be an “Axis” value, which is a number between 1 and 180 that tells the lab the exact angle at which the astigmatism correction needs to be placed.
Astigmatism is a common minor eye condition that causes blurred or distorted vision and can usually be corrected effectively with specifically shaped lenses in spectacles or contact lenses. It is important to remember that these numbers are not just added together; they work in tandem. The spherical part of the lens handles the overall distance blur, while the cylindrical part is “carved” into the lens at a specific angle to counteract the irregular shape of your cornea. Getting both these measurements exactly right is what allows an optician to provide you with “high definition” vision that is clear and proportional.
Corrective Lens Options for Combined Errors
For the majority of people in the UK, spectacles are the simplest way to correct a combination of myopia and astigmatism. Modern lens technology allows for “toric” spectacle lenses that are surprisingly thin and light, even for relatively high prescriptions. Because the lens has different powers in different directions, it is vital that the glasses are fitted accurately so that the lenses sit at the correct height and angle in front of your eyes. If the frames are bent or sit crookedly, the astigmatism correction will not be aligned with your eye, leading to blurred vision and strain.
For those who prefer contact lenses, “toric” soft lenses are designed specifically for this combination. These lenses are weighted or shaped in a way that they remain stable on the eye and do not rotate when you blink. This keeps the astigmatism correction perfectly aligned. If you have a very high level of astigmatism, rigid gas permeable (RGP) lenses might be recommended. Because these lenses are firm, they provide a perfectly smooth, new surface over your irregular cornea, often resulting in even sharper vision than spectacles or soft contact lenses for complex prescriptions.
Permanent Surgical Solutions
If you are looking for a more permanent way to manage both myopia and astigmatism, refractive surgery may be an option. Procedures like LASIK or LASEK use a specialized laser to reshape the cornea. The laser is programmed to flatten the central cornea to treat the myopia while simultaneously smoothing out the irregular curves to treat the astigmatism. Most patients with a stable prescription and healthy eyes can achieve very high levels of visual clarity without the need for glasses following these procedures.
The National Institute for Health and Care Excellence provides guidelines on the safety and effectiveness of laser eye surgery for various refractive errors. It is important to have a thorough pre-operative assessment with an eye surgeon to ensure your cornea is thick enough and your eyes are suitable for the laser. For those who are not candidates for laser surgery perhaps due to a very high prescription Refractive Lens Exchange (RLE) can be performed. This involves replacing the natural lens with an artificial “toric” intraocular lens that corrects both the short-sight and the astigmatism from inside the eye.
Conclusion
Short-sight and astigmatism very frequently occur together because the same factors that cause the eye to grow long often cause the cornea to become irregularly shaped. This combined error leads to vision that is both blurred and distorted at all distances. Fortunately, modern “toric” lenses in spectacles and contact lenses, as well as advanced surgical procedures, provide highly effective ways to correct these issues and restore clear, comfortable sight.
If you experience severe, sudden, or worsening symptoms, call 999 immediately.
Is it harder to get a prescription right if I have both conditions?
No, modern digital equipment allows opticians to measure combined errors very precisely, though it may take a few more minutes to fine-tune the “Axis” of your astigmatism.
Can I wear regular contact lenses if I have a small amount of astigmatism?
If your astigmatism is very low, your optician might be able to incorporate it into a standard spherical lens, but most people see much more clearly with a proper “toric” lens.
Will laser surgery fix both my short-sight and my astigmatism
Yes, modern lasers are designed to treat both spherical and cylindrical errors in a single procedure, provided your eyes are otherwise healthy and suitable.
Why do my glasses feel thicker if I have astigmatism?
The cylindrical part of the lens has a different thickness in different directions, which can sometimes make the edges of the lens look slightly more pronounced.
Can astigmatism go away if I treat my short-sightedness?
No, they are separate physical issues. Reshaping the eye to fix the distance focus (myopia) does not automatically smooth out the irregular curves (astigmatism).
Are toric contact lenses more expensive than regular ones?
Yes, they are generally slightly more expensive because the manufacturing process is more complex and they require a more detailed fitting by your optician.
Is it normal to see “streaks” from car lights if I have both?
Yes, this is a very common symptom of uncorrected or under-corrected astigmatism combined with short-sight, particularly in low-light conditions.
Authority Snapshot
This article provides educational information on the coexistence and management of myopia and astigmatism within the United Kingdom. The content is reviewed by Dr. Stefan Petrov to ensure alignment with current NHS and clinical knowledge regarding refractive errors and visual health. Our goal is to empower patients with accurate and safe information to help them understand their combined prescriptions and maintain long term ocular wellbeing.
