Astigmatism is a common vision condition characterized by an irregularly shaped cornea or lens. Its effects often become more noticeable in low-light environments, such as during nighttime.
What is Astigmatism
Astigmatism occurs when the eye’s cornea, the clear front surface, or the lens inside the eye has an irregular curvature. Instead of being perfectly round, like a basketball, it’s shaped more like an American football or the back of a spoon. This irregular shape causes light to bend unevenly, preventing it from focusing sharply onto a single point on the retina, the light-sensitive tissue at the back of the eye. Vision becomes blurred or distorted at all distances. This condition is a type of refractive error, meaning the eye does not refract, or bend, light correctly.
Why Night Vision Worsens
The impact of astigmatism often worsens in low-light conditions due to the natural dilation of the pupils; in dim environments, the pupil, the opening that controls the amount of light entering the eye, enlarges to allow more light to reach the retina. This dilation exposes a larger area of the irregularly shaped cornea or lens. When more of the imperfect surface is utilized, light rays scatter unevenly, intensifying the blur and distortion. This increased light scatter prevents light from focusing precisely, exacerbating visual issues that are less apparent in brighter conditions when the pupil is smaller and only the central, regular part of the lens or cornea is used. Pupil dilation amplifies the effects of the eye’s irregular curvature.
How Astigmatism Affects Night Vision
At night, astigmatism causes specific visual disturbances:
- Halos often appear as bright rings or glows around light sources, such as streetlights or oncoming headlights.
- Glare, an intense and often uncomfortable brightness, can be particularly pronounced from headlights, making it challenging to focus.
- Starbursts manifest as streaks or rays radiating outwards from points of light, transforming distinct light sources into blurred, star-like patterns.
- Ghosting, or double vision, causes objects or lights to appear with a faint, secondary image offset from the main one.
These effects can significantly impair night vision and make activities like driving more challenging.
Correction and Practical Steps
Correcting astigmatism involves methods designed to compensate for the eye’s irregular shape. Eyeglasses with cylindrical lenses are a common solution, specifically designed to correct the uneven bending of light. Contact lenses, particularly toric lenses, are another effective option; these have a unique design that ensures they remain properly oriented on the eye. For a more permanent solution, refractive surgeries like LASIK (Laser-Assisted In Situ Keratomileusis) and PRK (Photorefractive Keratectomy) reshape the cornea.
Beyond corrective lenses or surgery, practical steps can help manage astigmatism’s effects at night. Ensure your vision prescription is up-to-date, as an accurate prescription helps optimize clarity. Anti-glare coatings on eyeglasses reduce reflections and improve comfort, especially from bright lights. Keeping vehicle windshields and mirrors clean also minimizes glare and maintains optimal visibility. If night vision remains challenging, consult an eye care professional for tailored advice and solutions.