Astigmatism is one of the most common vision problems, categorized alongside nearsightedness and farsightedness. This refractive error occurs when the eye does not focus light evenly onto the retina.
Defining the Condition and Visual Distortion
Astigmatism is characterized by an imperfection in the curvature of the eye’s light-gathering surfaces. Instead of the cornea and lens being uniformly rounded like a basketball, one or both surfaces are curved more steeply in one direction, similar to the shape of an American football. This uneven shape prevents light rays from refracting correctly as they enter the eye.
In an eye without astigmatism, light converges to a single, sharp focal point directly on the retina. However, the irregular curvature of an astigmatic eye causes incoming light to focus on multiple points, either in front of, behind, or on the retina. This results in blurred or distorted vision that affects clarity at any distance.
Recognizing the Common Symptoms
The most noticeable symptom of astigmatism is blurriness or distortion of vision, often present at all viewing distances. Straight lines may appear wavy, tilted, or ghosted. This persistent lack of clarity causes the eyes to work harder to compensate for the distortion.
Prolonged visual effort often leads to eye strain, discomfort, and frequent tension headaches, especially after tasks requiring intense focus, such as reading or computer work. Astigmatism also affects night vision because the pupil dilates in low light, allowing more peripheral light to enter the eye. This increased light scattering magnifies the distortion, causing headlights and streetlights to appear with halos, starbursts, or streaks.
What Causes the Irregular Shape
Astigmatism stems from irregularities in two different structures within the eye. The most common form, Corneal Astigmatism, is caused by a misshapen cornea, the clear, dome-shaped front surface of the eye. Lenticular Astigmatism occurs when the lens inside the eye has an uneven curvature.
The underlying reason for these mismatched curves is often a genetic predisposition, meaning the condition is commonly present from birth. The degree of astigmatism can change throughout a person’s life due to eye surgery, trauma, or the progression of other eye conditions. For instance, keratoconus causes the cornea to progressively thin and bulge outward into a cone shape, which worsens astigmatism.
Options for Correcting Astigmatism
Correction focuses on counteracting the way the irregular shape distorts light entering the eye. The simplest and most common method is using prescription eyeglasses. The lenses in these glasses are ground with a cylindrical power to compensate for the eye’s uneven curvature, directing the light to a single focal point on the retina.
Contact Lenses
Specialized contact lenses offer an effective solution. These are known as toric contact lenses, which differ from standard spherical lenses. Toric lenses have two different power meridians to correct both the spherical and cylinder errors associated with astigmatism. They are also designed with stabilizing features, such as weighted areas, to ensure they remain correctly oriented on the eye and prevent rotation.
Surgical Options
Permanent correction is available through refractive surgery, with procedures like LASIK being the most well-known option. During LASIK, a precise laser is used to reshape the curvature of the cornea itself, permanently correcting the irregular surface. Other surgical options, such as the implantation of toric intraocular lenses, may be considered for individuals with high astigmatism or those undergoing cataract surgery.