ASTIGMATISM: REGULAR AND IRREGULAR
What Is Astigmatism?
Astigmatism occurs when the cornea (the clear front surface of the eye) or, less commonly, the lens inside the eye, has an irregular curvature rather than a smooth, evenly rounded shape. Instead of focusing light to a single sharp point on the retina, an astigmatic eye focuses light at multiple points, resulting in blurred or distorted vision at all distances. Common symptoms include blurry vision, glare, halos around lights, eye strain, and headaches, especially with prolonged reading or screen use.
There are two distinct categories of astigmatism, and the distinction matters significantly for treatment.
Regular Astigmatism
Regular astigmatism is by far the most common type. In this form, the cornea is shaped more like a football than a basketball — steeper in one direction and flatter in the direction perpendicular to it, but consistently and symmetrically so across the corneal surface. This predictable pattern means the astigmatism can be measured and corrected in a straightforward way, and it typically has genetic origins or develops gradually as a normal variation in eye shape.
Irregular Astigmatism
Irregular astigmatism occurs when the cornea’s surface is asymmetric and doesn’t follow a smooth, predictable pattern — the curvature varies unevenly across different points of the cornea rather than in two consistent, opposite directions. This type is less common and is usually caused by an underlying corneal condition or event, such as:
- Keratoconus, a progressive thinning and bulging of the cornea
- Corneal scarring, from injury, infection, or prior surgery
- Irregular healing after eye surgery, including certain complications of refractive or corneal procedures
- Corneal dystrophies, a group of inherited conditions affecting corneal shape or clarity
Because irregular astigmatism doesn’t follow a uniform pattern, it’s generally harder to correct fully with glasses, and typically requires more specialized treatment approaches.
Treatment Options
The right treatment for astigmatism depends heavily on whether it’s regular or irregular, as well as its severity and whether cataracts or other eye conditions are also present.
Glasses
For most regular astigmatism, glasses with a cylindrical lens correction are a simple, effective, and non-invasive option. Glasses can fully correct regular astigmatism in the vast majority of cases. However, glasses are generally less effective for significant irregular astigmatism, since a flat lens can’t fully compensate for an unevenly shaped corneal surface.
Standard Soft Toric Contact Lenses
Soft toric contact lenses are specially designed with different powers in different meridians of the lens to correct regular astigmatism, offering an alternative to glasses for patients who prefer or need contact lenses. Like glasses, standard soft toric lenses work well for regular astigmatism but are typically insufficient for correcting irregular astigmatism, since they still rest on and take on some of the irregular corneal shape underneath.
RGP (Rigid Gas Permeable) Contact Lenses
RGP lenses are rigid, oxygen-permeable lenses that hold their shape over the eye, effectively creating a new, smooth, and optically regular refracting surface in place of the irregular cornea underneath. This makes RGP lenses one of the most effective non-surgical options for correcting irregular astigmatism, particularly in conditions like keratoconus or corneal scarring, where soft lenses and glasses fall short. RGP lenses can also be used for regular astigmatism, though soft lenses or glasses are often preferred for comfort in those cases. Some patients with more complex irregular astigmatism may benefit from specialty designs, such as hybrid or scleral lenses, which combine a rigid optical center with a softer or larger skirt for improved comfort and stability.
Laser Vision Correction (LASIK/PRK)
For patients with regular astigmatism, laser vision correction can reshape the cornea to eliminate or significantly reduce the astigmatism itself, often allowing full independence from glasses or contacts. Because LASIK and PRK work by removing tissue in a precise, pre-planned pattern, they are generally not appropriate for correcting significant irregular astigmatism, and in some cases (such as keratoconus) are specifically avoided, since removing corneal tissue can worsen an already unstable or thinning cornea.
Toric Intraocular Lenses (IOLs)
For patients with regular astigmatism who are undergoing cataract surgery, a toric IOL can correct the astigmatism at the same time the cataract is removed. These lenses have additional focusing power built into a specific area of the lens to directly counteract the eye’s astigmatism, often eliminating or greatly reducing the need for glasses after surgery. Toric IOLs are designed for regular astigmatism and require precise measurement and rotational positioning during surgery to work effectively.
Additional Options for Irregular Astigmatism
For more advanced irregular astigmatism, particularly from progressive conditions like keratoconus, additional treatments may be recommended to stabilize the cornea or improve its shape, such as corneal cross-linking (to halt progression) or, in severe cases, corneal transplant. These are typically considered when contact lenses and other conservative measures aren’t sufficient.
Finding the Right Option for You
Because regular and irregular astigmatism require different treatment approaches, an accurate diagnosis is the essential first step. During your exam, we use detailed corneal mapping (corneal topography) to characterize the exact pattern of your astigmatism and determine which correction options — glasses, contacts, laser vision correction, or surgical lens options — will give you the clearest, most stable vision.
If you have astigmatism and want to explore your correction options, schedule a consultation with us to determine the best approach for your eyes.