Astigmatism: Causes, Symptoms, and Treatment Options

What Is Astigmatism?

A normal cornea is roughly spherical, like a soccer ball — equally curved in all directions. In astigmatism, the cornea (or in some cases the crystalline lens inside the eye) has unequal curvature across different meridians, making it shaped more like a rugby ball. One meridian is steeper than the one perpendicular to it.

Because the front surface of the eye curves differently in different directions, incoming light refracts at different angles and focuses at multiple points rather than a single sharp point on the retina. The result is blur or distortion at everyviewing distance — unlike short-sightedness (myopia), where only distant objects blur, or long-sightedness (hyperopia), where near objects may be the primary problem.

Astigmatism is a refractive error, not a disease of the eye. It is extremely common and can occur on its own or alongside myopia or hyperopia.

Types of Astigmatism

Astigmatism is classified by its source and by its geometry:

• Corneal astigmatism— the most common form. Unequal curvature of the corneal surface itself. Measured directly by keratometry or corneal topography.
• Lenticular astigmatism— caused by the crystalline lens inside the eye having an irregular shape. Less common; becomes relevant when planning intraocular lens selection for cataract surgery.

Geometrically, astigmatism is either regular or irregular:

• Regular astigmatism— the two principal meridians are at 90° to each other. This is the most common pattern and can be fully corrected with cylindrical spectacle lenses or toric contact lenses.
• Irregular astigmatism— the corneal curvature varies in a more complex, unpredictable pattern. Caused by keratoconus, corneal scarring from infection or injury, or prior corneal surgery. Standard spectacle lenses cannot adequately correct irregular astigmatism; rigid gas-permeable (RGP) or scleral contact lenses are typically required.

Symptoms

The hallmark of astigmatism is blur or distortion that is present at all distances, not just near or far. Common symptoms include:

• • Blurred or distorted vision at all distances
• • Ghosting or doubling of images (particularly around letters and edges)
• • Eyestrain and eye fatigue, especially after reading or screen work
• • Headaches, typically frontal or temporal
• • Difficulty seeing fine detail, such as small print
• • Squinting in an attempt to sharpen vision
• • Night-time glare or haloes around lights (particularly with high astigmatism)

Low degrees of astigmatism may cause no noticeable symptoms at all and are discovered incidentally during a routine eye examination.

Causes

Most astigmatism is determined by the inherited shape of the cornea — it is present from birth and remains relatively stable through adult life. Contributing factors include:

• Genetics— corneal shape is strongly heritable; having a parent with significant astigmatism increases your likelihood of developing it.
• Keratoconus— a progressive corneal condition in which the cornea thins and steepens irregularly, causing worsening irregular astigmatism. Often presents in adolescence or early adulthood.
• Eyelid lesions— ptosis (drooping eyelid), large chalazion, or lid tumours can press on the cornea and induce or worsen astigmatism. Removing the lesion can partially reverse this.
• Corneal scarring— from infection (viral, bacterial, or acanthamoeba keratitis) or trauma, which distorts the normally smooth corneal surface.
• Prior eye surgery— incisions from previous cataract or corneal surgery can induce post-surgical astigmatism.

Diagnosis

Astigmatism is detected during a comprehensive eye examination using several complementary tests:

• • Autorefraction — automated objective measurement of refractive error including cylinder axis and power
• • Subjective refraction — the optometrist or ophthalmologist refines the measurement by testing which lens combination gives the sharpest vision
• • Keratometry — measures the curvature of the central cornea across two principal meridians
• • Corneal topography — produces a detailed colour map of the entire corneal surface, essential for detecting irregular astigmatism and keratoconus

Treatment Options

The appropriate correction for astigmatism depends on its type, degree, and the patient’s lifestyle and goals:

• Spectacles— incorporate a cylindrical lens component to compensate for the unequal corneal curvature. Effective for all regular astigmatism.
• Soft toric contact lenses— specially designed lenses with weighted zones to keep them oriented correctly on the eye. Widely available and suitable for low to moderate regular astigmatism.
• Rigid gas-permeable (RGP) lenses— the rigid lens vaults over the irregular corneal surface, neutralising much of the astigmatism. The treatment of choice for irregular astigmatism.
• Scleral contact lenses— larger rigid lenses that rest on the sclera and fully vault the cornea, providing excellent vision and comfort for severe irregular astigmatism or keratoconus.
• LASIK / PRK— laser refractive surgery can correct regular astigmatism up to approximately 4.00–6.00D, depending on available corneal thickness. Not suitable for irregular astigmatism or keratoconus.
• Toric intraocular lens (IOL)— when cataract surgery is planned, a toric IOL corrects corneal astigmatism at the same time as removing the clouded lens, reducing or eliminating the need for distance glasses.
• Corneal cross-linking (CXL)— for keratoconus, cross-linking halts progression by strengthening corneal collagen. It does not reverse existing astigmatism but prevents further worsening.

Frequently Asked Questions