Astigmatism worsens when something changes the shape of your cornea or lens, and several factors can do this, from habitual eye rubbing to normal aging. Most people with mild astigmatism stay stable for years, but certain conditions and behaviors can push it in the wrong direction. Understanding what drives progression helps you recognize early warning signs and protect your vision.
How Astigmatism Progression Is Measured
Eye care professionals track astigmatism in units called diopters. A change of 0.25 or 0.50 diopters over several years is common and usually nothing to worry about. In children aged 6 to 12, more than 0.50 diopters of astigmatic change over three years is considered atypical and warrants further investigation with corneal mapping to rule out underlying conditions like keratoconus.
For adults, any noticeable shift in astigmatism between routine eye exams, especially if it seems to accelerate, is worth discussing with your eye care provider. A single measurement doesn’t tell the whole story. The pattern over time is what matters.
Eye Rubbing and Corneal Damage
Chronic, vigorous eye rubbing is one of the most controllable risk factors for worsening astigmatism. When you press hard on your eyes, you create large spikes in pressure inside the eye, thin the outer layer of the cornea, and trigger inflammatory chemicals in your tears. Over time, the structural “glue” between the collagen fibers that give your cornea its shape starts to break down. This loss of internal strength allows the cornea to bulge and warp under normal eye pressure, creating or worsening irregular astigmatism.
The rubbing also raises corneal temperature, disrupts enzyme activity, and can physically displace the gel-like substance that fills the spaces between collagen fibers. Think of it like repeatedly kneading a firm rubber ball until it loses its rigidity and starts to deform. People with allergies are especially vulnerable because itchy eyes make rubbing feel almost involuntary. If you rub your eyes frequently, breaking the habit is one of the most effective things you can do to slow progression.
Keratoconus: The Hidden Accelerator
Keratoconus is a progressive condition where the cornea thins and bulges into a cone-like shape, producing irregular astigmatism that gets worse over time. It typically starts in the teens or twenties and can progress for a decade or more. What makes it tricky is that the earliest changes often happen on the back surface of the cornea, while the front surface still looks normal. A standard eye exam can miss this entirely.
In subclinical keratoconus, the cornea’s thinnest point shifts downward and the back surface starts to bulge before you notice any symptoms at all. This means your astigmatism can be worsening for biological reasons long before your glasses prescription seems to change dramatically. Corneal topography, a painless imaging test that maps the surface of your eye in detail, is the best way to catch it early. If your astigmatism is increasing faster than expected, especially if it’s becoming more irregular or harder to correct with glasses, keratoconus screening is an important next step.
The good news: a treatment called corneal cross-linking can halt keratoconus progression. It works by strengthening the bonds between collagen fibers in the cornea using riboflavin drops and ultraviolet light. In a study of 610 eyes followed for three years, 99.2% remained stable after cross-linking with no further progression. The earlier it’s caught, the more vision you preserve.
Aging and the Corneal Shift
Even in healthy eyes, astigmatism changes direction as you age. In younger people, the steepest curve of the cornea typically runs vertically, a pattern called “with-the-rule” astigmatism. Over decades, the cornea gradually flattens in the vertical meridian and steepens horizontally, shifting to “against-the-rule” astigmatism. This transition generally happens between ages 55 and 65 for most people.
The back surface of the cornea follows the same pattern but more slowly, completing its shift closer to age 75 to 80. These changes are normal and happen to nearly everyone. They’re the main reason your glasses prescription keeps shifting slightly even when nothing else is wrong with your eyes. The shifts are usually gradual enough that updated lenses every year or two keep your vision sharp.
Lens Changes and Cataracts
Your cornea isn’t the only structure that affects astigmatism. The crystalline lens inside your eye also contributes. As you age, the proteins in this lens break down, clump together, and change its internal structure. This process, which eventually leads to cataracts, alters how the lens bends light and can introduce or worsen astigmatism.
When lens proteins form large insoluble clumps, they create uneven areas with different refractive properties. The result is scattered, distorted light rather than a clean focal point. This type of lenticular astigmatism doesn’t respond to corneal treatments and is only fully corrected when the clouded lens is replaced during cataract surgery. If your astigmatism is increasing in your 50s or 60s and your corneal measurements haven’t changed much, the lens is the likely culprit.
Blood Sugar Fluctuations
Diabetes can cause temporary but noticeable swings in your vision, including astigmatism changes. When blood sugar drops rapidly during treatment, the lens absorbs water from the surrounding fluid, changing its refractive power. In one study, patients undergoing glycemic control experienced hyperopic shifts ranging from 0.50 to 3.20 diopters. That’s a significant change, enough to make your current glasses feel completely wrong.
Interestingly, these shifts happen without measurable changes in lens thickness, anterior chamber depth, or eye length. The best current explanation is that hydration changes within the lens cortex subtly alter its internal focusing power. These fluctuations are typically temporary, resolving as blood sugar stabilizes, but they can be alarming if you don’t know what’s causing them. If you have diabetes and your vision seems to change day to day, getting your prescription checked during a period of stable blood sugar gives the most accurate result.
Eyelid Lumps and Pressure on the Cornea
A chalazion, the firm bump that forms when an oil gland in your eyelid gets blocked, can physically press on your cornea and distort its shape. The effect depends on the size and location of the lump. Chalazia in the middle of the upper eyelid cause the most astigmatism because they sit directly above the center of the cornea, where the pressure has the greatest warping effect.
Larger chalazia produce significantly more corneal distortion than smaller ones. The astigmatism they cause is usually temporary, resolving once the bump is treated or drains on its own. But recurrent chalazia, or ones that persist for months, can create longer-lasting corneal changes. If you notice your vision shifting and you have a bump on your eyelid, the two are likely connected.
Refractive Surgery Complications
Laser eye surgery corrects astigmatism by reshaping the cornea, but in rare cases, the cornea can become unstable afterward and begin to bulge, a complication called ectasia. This creates new irregular astigmatism that’s often harder to correct than the original problem. The risk varies by procedure: LASIK carries the highest rate at about 90 per 100,000 eyes, followed by surface ablation procedures at 20 per 100,000 and small-incision procedures at 11 per 100,000.
These numbers reflect cases even in eyes with no identifiable risk factors beforehand. The risk increases in people who had undetected subclinical keratoconus, thinner corneas, or high prescriptions before surgery. Post-surgical ectasia can appear months or years after the procedure. If you’ve had laser vision correction and your vision is gradually getting blurrier, corneal mapping can determine whether ectasia is developing.