Astigmatism is measured in diopters (D), and the number that tells you how bad yours is appears on your prescription as “CYL” or cylinder. Under 1.50 D is generally considered mild, 1.50 to 2.50 D is moderate, and anything above 2.50 D is significant or severe. Most people with astigmatism fall into the mild category, so if your number is below 1.50, you’re in the majority.
How to Find Your Number
Your eyeglass or contact lens prescription has three main values for each eye. The first (SPH or sphere) corrects nearsightedness or farsightedness. The second, labeled CYL or cylinder, is the one that measures your astigmatism. It tells you how much difference exists between the two curves of your cornea. A perfectly round cornea would have a cylinder of zero. The more oval or football-shaped your cornea is, the higher that number.
You’ll also see a number labeled “Axis,” written in degrees between 1 and 180. This doesn’t measure severity. It simply indicates the angle at which the uneven curvature sits on your cornea, so your lenses can be oriented correctly.
Mild, Moderate, and Severe Ranges
There’s no single universal cutoff, but the most commonly used classification breaks down like this:
- Mild: under 1.50 D. This is where the vast majority of people land. Studies across multiple countries found that 33 to 82% of people with astigmatism fall into this range. You might notice slight blurriness, especially at night, or you might not notice anything at all. Many people with mild astigmatism don’t need correction, or they get by with standard glasses.
- Moderate: 1.50 to 2.50 D. Vision is noticeably blurry at multiple distances without correction. You’re more likely to experience eyestrain, headaches, and difficulty driving at night. Starbursts and halos around lights become more pronounced. Correction makes a real difference at this level.
- Severe: above 2.50 D. Vision without correction is significantly distorted. Straight lines may appear tilted or wavy, and reading small text becomes difficult even at comfortable distances. Standard soft contact lenses won’t fully correct the problem, and specialty lenses or surgery are often part of the conversation.
Some classification systems place the moderate-to-severe boundary at 2.00 D instead of 2.50, so don’t worry if you see slightly different numbers elsewhere. The key point is the same: below 1.50 is mild, and above 2.00 to 2.50 starts getting into territory where correction becomes more important and more complex.
What Each Level Feels Like
Mild astigmatism often goes unnoticed during the day. Your brain is surprisingly good at compensating for small amounts of blur, especially in bright light when your pupils are small. The most common giveaway is trouble at night: headlights smear, streetlights develop little spikes, and road signs get harder to read. You might also catch yourself squinting more than you realize.
At moderate levels, daytime vision starts to suffer. Text on screens may look slightly doubled or “ghosted,” and you’ll find yourself holding your phone at arm’s length or leaning closer to your monitor. Eyestrain and headaches tend to build over the course of the day, especially if your work involves sustained reading or screen time.
Severe astigmatism makes uncorrected vision unreliable for most tasks. The blur isn’t uniform, either. Because one curve of your cornea is much steeper than the other, objects look stretched or distorted in a specific direction rather than just fuzzy all over. This directional distortion is what separates astigmatism from simple nearsightedness or farsightedness.
Correction Options by Severity
For mild astigmatism, standard glasses handle it easily. If you wear contact lenses, your eye care provider may decide that a regular spherical lens is good enough, particularly if your cylinder is 0.75 D or less. Whether a low cylinder needs a specialized toric lens depends on factors like which eye is dominant, the axis of the astigmatism, and how visually demanding your daily life is.
Once you cross into moderate territory, toric contact lenses (designed with different powers at different angles) become important for sharp vision. Glasses remain effective at any level, though higher cylinders mean the lenses get thicker on one edge and thinner on the other, which some people find cosmetically annoying or uncomfortable in lighter frames.
For severe astigmatism, rigid gas-permeable lenses or specialty scleral lenses often outperform soft torics because the rigid surface creates its own smooth optical surface over the irregular cornea. If you’d rather skip lenses altogether, laser surgery (LASIK or PRK) can correct up to about 6.00 D of astigmatism with current FDA-approved systems. Beyond that, or when laser surgery isn’t suitable, options like implantable toric lenses or refractive lens exchange come into play. The choice between these depends heavily on age, overall eye health, and the presence of other refractive errors.
Does Astigmatism Get Worse Over Time?
In children, high astigmatism often decreases naturally as the eye grows and the cornea reshapes itself during a process called emmetropization. By early adulthood, the prescription usually stabilizes. That said, astigmatism does tend to creep upward again after age 40 or so.
The pattern also shifts direction with age. In younger adults, the steepest curve of the cornea typically runs vertically (called “with-the-rule” astigmatism). Over decades, the cornea gradually flattens along that vertical meridian, and the steepest curve rotates toward horizontal (“against-the-rule” astigmatism). This shift is driven by changes in corneal collagen, eyelid tension, and possibly the pull of the muscles surrounding the eye. It’s a slow process, not something that changes dramatically year to year, but it’s why your prescription axis might drift over time even if the cylinder number stays similar.
Genetics also play a role. If your parents have significant astigmatism, you’re more likely to develop it and more likely to see it progress. Certain corneal conditions like keratoconus can cause astigmatism to worsen rapidly and irregularly, which is a different situation from ordinary age-related changes.
Regular vs. Irregular Astigmatism
Everything above applies to regular astigmatism, where the cornea has two cleanly defined curves (think of a football with a smooth surface). Glasses and standard toric lenses correct this type well. Irregular astigmatism is different: the corneal surface has multiple bumps or uneven zones that don’t follow a simple pattern. It can result from corneal diseases, eye injuries, or previous eye surgeries, and it also increases naturally with aging.
The practical difference is that irregular astigmatism can’t be fully corrected with standard glasses. If your vision still feels “off” even with an up-to-date prescription, irregular astigmatism may be the reason. Rigid or scleral contact lenses are typically the first-line solution, because the smooth lens surface overrides the cornea’s irregularities. Advanced corneal mapping (topography) can identify this type and guide treatment decisions.