Understanding the Astigmatism Severity Scale

Astigmatism is a common refractive error that causes blurry vision, eye strain, and vision distortion. However, not every case of astigmatism is equal.

Understanding the astigmatism severity scale can help you find the best solution to maintain sharp eyesight. In this article, we’ll discuss the severity scale, the impact of astigmatism, and possible treatment options.

What is the Astigmatism Severity Scale?

Astigmatism’s effects on your vision vary depending on the severity of your condition. To find your level of astigmatism, look at the cylinder (CYL) number on your glasses prescription.

The astigmatism severity scale ranges from mild (less than 1.00 diopter) to extreme (more than 3.00 diopters).

• Mild astigmatism (< 1.00 diopter). Mild astigmatism is common and often does not significantly affect vision, though some people may still benefit from corrective lenses for optimal clarity.
• Moderate astigmatism (1.00 to 2.00 diopters). Moderate astigmatism requires corrective lenses; laser eye surgery is an elective option.
• Severe astigmatism (2.00 to 3.00 diopters). Blurred vision from severe astigmatism can cause headaches that impact your health and day-to-day life.
• Extreme astigmatism (> 3.00 diopters). Extreme astigmatism reduces visual clarity at all distances. Without treatment, you won’t be able to see clearly at all. Corrective lenses or other interventions can significantly improve sharpness.

Visual Acuity and Symptoms by Severity

Severity Level	Typical Uncorrected Acuity	Common Symptoms
Mild	~20/20 to 20/30	Slight blur, occasional eyestrain
Moderate	~20/40 to 20/80	Noticeable blur, frequent squinting
Severe	~20/100 or worse	Major blur, distortion, frequent headaches
Extreme	~20/200 or worse	Severe distortion, limited daily function

What Do Astigmatism Numbers Mean?

Refractive errors are measured in diopters. A perfectly round eye with no astigmatism has 0 diopters. 

Most people have between 0.5 and 0.75 diopters of astigmatism. People who have 1.5 or more diopters of astigmatism usually need prescription glasses or contact lenses to see clearly.

What are the Symptoms of Astigmatism?

Mild cases are widespread, often causing minimal issues. However, moderate-to-severe astigmatism significantly impacts daily visual clarity.

Astigmatism symptoms generally include:

• Blurry vision
• Trouble seeing objects both close up and far away
• Fluctuating vision
• Double vision
• Eye strain
• Squinting
• Headaches
• Difficulty with night vision
• Seeing glares and halos at night
• Seeing shadowy images

How Does Astigmatism Affect Your Daily Life?

Leaving astigmatism uncorrected affects various aspects of your daily routine. These difficulties will be greater with higher levels of severity. 

Here’s how astigmatism can affect your life:

• Discomfort due to headaches and fatigue
• Reduced visual clarity
• Difficulties with driving safely, especially at night, due to halos, starbursts, and glare
• Digital eye strain from prolonged exposure to digital devices
• Problems at work or worsened performance

These side effects are especially problematic for specific professions that rely on precise and accurate vision.

What Causes Astigmatism?

Astigmatism occurs when the cornea or lens of your eye has an irregular shape, preventing light from focusing clearly on your retina.

The cornea's irregular shape is often compared to a football rather than a round shape. There are two main categories of astigmatism:

• Regular astigmatism. Symmetrical curvature differences, easily corrected with glasses or standard toric contact lenses.
• Irregular astigmatism. Uneven curvature often due to injury, keratoconus, or corneal surgery, typically needs specialized correction like rigid gas permeable (RGP) lenses.

How to Read Your Glasses Prescription

When your optometrist hands you a glasses prescription, it may seem complex, but it’s straightforward once you understand the terms:

• Sphere (SPH). Indicates whether you are nearsighted (-) or farsighted (+). The higher the number, the stronger the lens power needed to correct your vision.
• Cylinder (CYL). Measures the severity of astigmatism in diopters.
• Axis. Shows the orientation (angle) of astigmatism correction, ranging from 0° to 180°.

How is Astigmatism Treated?

Your treatment depends on the severity of your astigmatism, lifestyle, and personal comfort preferences. Available treatment options for astigmatism include:

• Glasses.  Ideal for mild to moderate astigmatism; inexpensive and easy. 
• Soft toric contact lenses. An excellent choice for mild-to-moderate astigmatism (up to approximately 2.75 D). 
• Rigid gas permeable (RGP) or scleral lenses. Best for moderate-to-high astigmatism, especially irregular types.
• Laser refractive surgery (LASIK, PRK, SMILE). Suitable primarily for mild-to-moderate regular astigmatism (usually under 4.00 D).
• Toric intraocular lenses (IOLs). Typically used during cataract surgery to correct astigmatism up to approximately 4.00 D.
• Corneal cross-linking and intracorneal rings. Recommended if your astigmatism is progressive due to keratoconus or other corneal disorders.