Astigmatism is a common refractive error that occurs when the cornea (the transparent layer at the front of the eye) or the lens (the focusing structure inside the eye) has an irregular curvature, preventing light from focusing on a single point on the retina. Normally, the eye has a round shape, like a basketball, but in astigmatism, it takes on an oval shape, resembling a rugby or American football. This irregularity causes light to refract unevenly across different meridians (horizontal, vertical, or oblique axes), resulting in blurred or distorted vision at both near and far distances. Astigmatism is often congenital and may coexist with other refractive errors such as myopia (nearsightedness) or hyperopia (farsightedness).

Types of Astigmatism

Astigmatism is classified based on its anatomical origin and refractive properties:

Corneal Astigmatism: The most common type, caused by irregular curvature of the cornea.
Lenticular Astigmatism: Arises from irregularities in the lens surface or position (e.g., lens subluxation or lenticonus).
Retinal Astigmatism: Rarely occurs due to the macula's oblique positioning (the retina's central part responsible for sharp vision).
Regular Astigmatism: The two principal meridians are perpendicular to each other, further categorized as:
"With-the-rule" astigmatism (steeper vertical meridian)
"Against-the-rule" astigmatism (steeper horizontal meridian)
"Oblique" astigmatism (neither horizontal nor vertical)
"Double oblique" astigmatism (principal meridians are not perpendicular)
Irregular Astigmatism occurs when the corneal surface has uneven curvatures. It is often seen in conditions like keratoconus or corneal scarring.
Simple, Compound, and Mixed Astigmatism: Defined based on whether light focuses in front of or behind the retina along different meridians.

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Symptoms of Astigmatism

Common symptoms of astigmatism include:

Blurred or distorted vision at all distances
Eye strain (asthenopia)
Headaches
Difficulty seeing at night
Objects appearing stretched or tilted
Frequent squinting to see clearly

Children may not notice these symptoms, making regular eye screenings crucial. If untreated, astigmatism in children can lead to amblyopia (lazy eye) or learning difficulties.

Causes and Risk Factors

The exact cause of astigmatism is not fully understood, but genetics play a significant role. It is often present from birth and inherited from parents. Other possible causes include:

Eye injuries
Keratoconus (a condition where the cornea thins and bulges into a cone shape)
Complications from eye surgery
Pressure exerted by the eyelids on the cornea
Environmental factors such as nutritional deficiencies or extraocular muscle tension

Astigmatism can change over time; for instance, high astigmatism in infancy often decreases around the age of one as the eye develops.

Epidemiology

Astigmatism affects approximately one in three people worldwide and varies with age and ethnicity:

Childhood: The cornea is steeper in infants (0-4 years), making against-the-rule astigmatism more common. Astigmatism generally decreases between ages 4-18 as the cornea flattens.
Adulthood: Astigmatism remains stable between 18-40 years but may increase in an against-the-rule direction after 40.
Ethnic Variations: Higher prevalence is reported in Asian and Hispanic populations, with studies indicating 33-36% of individuals having at least 1 diopter (D) of astigmatism.

Diagnosis

Astigmatism is diagnosed through a comprehensive eye examination, which may include:

Visual Acuity Test: Measures clarity of vision by reading letters or symbols.
Retinoscopy and Refraction: Evaluate how light bends in the eye and determine the appropriate lens power.
Keratometry and Topography: Measures corneal curvature and maps its surface.
Astigmatic Fan and Jackson Cross Cylinder: Confirms the axis and power of the cylindrical lens needed for correction.
Slit Lamp Examination: Examines the eye for structural abnormalities.

Treatment Options

Treatment for astigmatism depends on its severity and the patient's visual needs:

Optical Correction:
Eyeglasses: Cylindrical lenses correct the uneven refraction of light. If mild astigmatism (up to 0.5 D) is asymptomatic, it may not require correction.
Contact Lenses: Toric soft lenses or rigid gas permeable (RGP) lenses are effective, especially for higher astigmatism. RGP lenses help compensate for corneal irregularities.
Orthokeratology (Ortho-K): Nighttime wear of rigid lenses temporarily reshapes the cornea.
Surgical Interventions:
Refractive Surgery: LASIK, PRK, and epi-LASIK reshape the cornea to correct astigmatism (effective for 0.5-10 D).
Astigmatic Keratotomy (AK): Arcuate incisions in the cornea correct up to 4-6 D of astigmatism.
Limbal Relaxing Incisions (LRI): Used for mild astigmatism (1-2 D) with minimal complications.
Toric Intraocular Lens (IOL) Implantation: Special lenses implanted during cataract surgery correct astigmatism.
Corneal Wedge Resection: An option for severe astigmatism (10-20 D).
Special Cases:
Post-keratoplasty astigmatism may require suture adjustments or relaxing incisions.
Glasses are preferred for children, while contact lenses are less commonly used.

Prevention and Early Detection

Since astigmatism is primarily genetic or structural, it cannot be prevented. However, early diagnosis through routine eye exams ensures timely treatment. Vision screenings are particularly crucial in preschool and school-age children.

Prognosis and Complications

If treated early, astigmatism generally has a good prognosis. Vision can be corrected with glasses, contact lenses, or surgery. However, untreated astigmatism may lead to complications such as amblyopia (lazy eye), strabismus (eye misalignment), or permanent vision impairment. Progressive conditions like keratoconus require regular monitoring.

Astigmatism is a widespread refractive error affecting both children and adults. Influenced by genetic and environmental factors, it can be effectively managed with modern diagnostic and treatment methods. Regular eye check-ups, early intervention, and personalized treatment strategies significantly enhance the quality of life for individuals with astigmatism.

Astigmatism