Astigmatism contacts are specialized contact lenses designed to correct a common vision condition known as astigmatism. These lenses provide clear vision for individuals whose eyes have an irregular shape, which affects how light is focused onto the retina. Unlike standard contact lenses that address nearsightedness or farsightedness, astigmatism contacts feature a unique design tailored to compensate for these specific irregularities.
Understanding Astigmatism
Astigmatism is a refractive error where the eye’s shape, specifically the cornea or the lens inside the eye, has mismatched curves. Instead of being perfectly round, like a basketball, the astigmatic eye is often shaped more like a football or the back of a spoon. This irregular curvature causes light entering the eye to bend unevenly, focusing on multiple points on the retina instead of a single, sharp point.
This uneven focusing of light results in blurred or distorted vision at all distances. Astigmatism can occur alone or in combination with other refractive errors, such as nearsightedness (myopia) or farsightedness (hyperopia). The condition is often present from birth, can be hereditary, or may develop due to eye injury, disease, or surgery.
How Toric Lenses Correct Vision
The specialized contact lenses used to correct astigmatism are called toric lenses. These lenses have a unique design that features different optical powers in two orientations perpendicular to each other, much like a slice taken from the side of a donut. This allows the lens to compensate for the irregular curvature of an astigmatic eye, ensuring light focuses correctly on the retina for clear vision.
An important aspect of toric lenses is their ability to remain stable on the eye. Because the corrective power is specific to certain meridians, the lens must maintain a precise orientation to provide effective vision correction. To achieve this stability, manufacturers incorporate various design features.
Common stabilization methods include prism ballast, where the lens is designed with a thicker or heavier bottom edge, allowing gravity and eyelid pressure. Other designs use thin zones or truncation, which involve varying lens thickness or slightly flattening the bottom edge to interact with the eyelids and prevent rotation. Some designs, like the BLINK STABILIZED™ design, work with eyelid movements to realign the lens with each blink, maintaining clear and stable vision.
Types and Practical Considerations
Toric contact lenses are available in various types. The most common are soft toric lenses, made from flexible hydrogel or silicone hydrogel materials, which are comfortable and available in daily disposable, bi-weekly, and monthly replacement schedules. Rigid gas permeable (RGP) lenses are another option, particularly for more complex or severe astigmatism, as they maintain their shape on the eye, providing a consistent refractive surface.
Obtaining toric lenses requires a specialized fitting by an eye care professional. This is because the precise orientation of the lens on the eye is important for proper vision correction. The eye care specialist will assess the severity of astigmatism, the eye’s condition, and lifestyle preferences to recommend the most suitable type and material. Following proper lens hygiene and adhering to the prescribed replacement schedule are important for maintaining lens performance and eye health.