Astigmatism is a common vision condition that arises from an imperfection in the curvature of the eye’s cornea or lens. It causes light to bend unevenly as it enters the eye, leading to blurred or distorted vision. Affecting approximately one-third of people globally, astigmatism makes objects appear blurry or wavy, both up close and far away.
Understanding Astigmatism
Astigmatism occurs when the cornea or the lens inside the eye has an irregular curve. Instead of being perfectly spherical like a basketball, the affected eye more closely resembles the shape of a football or the back of a spoon. This irregular shape means that light rays entering the eye do not focus precisely at a single point on the retina.
The retina converts light into electrical signals that are sent to the brain, forming the images we see. With astigmatism, the uneven bending of light causes it to scatter across multiple focal points on the retina instead of converging to one. This prevents a clear, sharp image from forming, resulting in blurred or distorted vision at all distances.
The Visual Experience of Astigmatism
Fine details can be difficult to discern, whether it’s reading small text on a menu or recognizing letters on a distant road sign. Objects may also seem elongated, duplicated, or shadowy, creating a ghost-like effect around their edges.
Light sources, especially at night, are a commonly reported visual effect. Headlights, streetlights, or other bright lights can appear with halos, starbursts, or streaks extending from them. This can make nighttime driving challenging.
Beyond visual distortions, astigmatism can lead to other symptoms as the eyes work harder to compensate for the uneven focus. People often experience persistent eye strain and fatigue, particularly after prolonged tasks like reading or looking at screens. Headaches are also a common complaint, stemming from the continuous effort to achieve clearer vision.
Classifications of Astigmatism
Astigmatism is categorized based on the regularity of the eye’s curvature and how light focuses relative to the retina. Regular astigmatism is the most common form, where the principal meridians (the steepest and flattest curves of the eye) are 90 degrees apart. This type results from a uniform curvature in one direction and is often correctable with standard corrective lenses.
In contrast, irregular astigmatism involves an uneven curvature across multiple axes, meaning the principal meridians are not perpendicular. This type is less common and often results from eye injuries, scarring, or conditions like keratoconus, which causes the cornea to thin and bulge into a cone shape. Irregular astigmatism can be more challenging to correct with conventional glasses or contact lenses. Astigmatism is also classified by how light focuses: myopic astigmatism occurs when light focuses in front of the retina, hyperopic astigmatism when light focuses behind it, and mixed astigmatism when one focal point is in front and the other is behind the retina.
Managing Astigmatism
Managing astigmatism often involves corrective lenses designed to compensate for the eye’s irregular shape. Glasses are a straightforward solution, with lenses specifically ground to counteract the uneven refraction of light. Toric contact lenses offer another option, designed with different powers in different meridians to correct the astigmatism.
For a more permanent solution, refractive surgery can reshape the cornea to improve how light focuses on the retina. LASIK (Laser-Assisted In Situ Keratomileusis) involves creating a thin flap on the cornea, reshaping the underlying tissue with a laser, and then repositioning the flap. PRK (Photorefractive Keratectomy) reshapes the corneal surface after the outer layer is gently removed, which then regenerates. SMILE (Small Incision Lenticule Extraction) is a newer, minimally invasive procedure that creates a small lenticule (a thin layer of corneal tissue) within the cornea, which is then removed through a tiny incision, reshaping the cornea without creating a flap. An eye care professional can determine the most suitable course of action based on individual needs and the characteristics of their astigmatism.