Astigmatism is a common imperfection in the eye’s structure where the cornea, or sometimes the lens, has an irregular curvature. Instead of being shaped like a sphere, the surface is curved more like a football. This altered shape prevents light from bending evenly, meaning the eye cannot focus light onto a single point on the retina. This refractive error results in blurred or distorted vision at any distance and causes visual phenomena like light streaks, halos, and starbursts, which are particularly noticeable in low-light conditions.
Understanding Light Distortion
The physical mechanism behind seeing light streaks is the irregular way the astigmatic eye refracts light. Because the light rays are split, the visual image is stretched or smeared across the retina in one direction. For a bright point source of light, such as a headlight or streetlamp, this effect is perceived as a streak, a halo, or a starburst. The specific appearance of the streak—whether horizontal, vertical, or diagonal—depends on the axis of the greatest curvature in the eye.
These light distortions become significantly more pronounced in low-light environments, such as during nighttime driving. In the dark, the eye’s pupil dilates to allow more light in, forcing light to pass through the peripheral areas of the lens and cornea. Since the periphery often has greater irregularities, the increased amount of distorted light entering the dilated pupil exaggerates the streaking and glare effects.
Other Visual and Physical Symptoms
Astigmatism presents with several visual and physical symptoms beyond light distortion. The most pervasive symptom is a general blurriness or distortion of vision, affecting both near and distance viewing. Objects may appear warped or wavy, making tasks that require fine detail challenging.
To compensate for the blurry image, individuals with uncorrected astigmatism frequently squint to temporarily sharpen their vision. This constant effort to focus, particularly during activities like reading or prolonged screen time, leads to significant eye strain and discomfort.
The chronic strain on the eye muscles can also manifest as frequent headaches. These headaches are often reported after extended periods of visual concentration, as the eyes work harder to overcome the focusing error. If these symptoms occur alongside light streaking, a comprehensive eye evaluation is necessary.
Getting Diagnosed and Corrective Options
Diagnosing astigmatism requires a comprehensive eye examination performed by an eye care professional. The process involves a visual acuity test, where the patient reads letters on a chart, and a refraction test, which determines the precise lens power needed to correct the focusing error.
Diagnosis
A specialized test called keratometry is performed to measure the curvature of the cornea’s surface. This test helps the doctor determine the amount and axis of the corneal astigmatism, which is necessary for prescribing corrective lenses. The results of these measurements are used to determine the appropriate corrective options.
Corrective Options
The most common treatment is the use of corrective lenses, either eyeglasses or contact lenses, which compensate for the eye’s irregular shape. Eyeglass lenses are designed to bend light properly, ensuring it focuses as a single point on the retina. For contact lenses, specialized soft or rigid lenses known as toric lenses are used; these have different powers in various meridians to precisely correct the astigmatism.
For those seeking a permanent solution, refractive surgery options like LASIK or Photorefractive Keratectomy (PRK) can be considered. These procedures use a laser to precisely reshape the curvature of the cornea, correcting the refractive error and reducing or eliminating the need for glasses or contacts. An eye care professional will evaluate a patient’s condition to determine if they are a suitable candidate for surgery.