Contact lenses designed to correct astigmatism are highly effective for most people seeking an alternative to glasses. These specialized lenses successfully correct the vision distortion caused by an irregularly shaped eye surface, which is a common refractive error. The success of astigmatism contact lenses relies on the unique design of the lens and a precise fitting process performed by an eye care professional. They offer a stable and clear visual experience once the correct parameters and lens type are determined.
What Astigmatism Is and How Lenses Correct It
Astigmatism is a condition where the eye’s front surface (cornea) or the lens inside the eye has an uneven curvature. Instead of being shaped like a perfectly round basketball, the astigmatic eye is shaped more like an American football. This irregular shape causes light entering the eye to refract, or bend, unevenly, preventing it from focusing sharply onto a single point on the retina. The result is blurred or distorted vision at all distances, which may also be accompanied by symptoms like eye strain or headaches.
A normal, spherical lens is not able to counteract this uneven light focusing because it has the same corrective power across its entire surface. Correcting astigmatism requires applying different refractive powers across different meridians of the lens. The contact lens must neutralize the irregular curvature by incorporating a cylinder power component that is aligned precisely with the steepest and flattest axes of the eye’s surface. This specialized design ensures that the scattered light rays are bent correctly to converge onto a single point, restoring sharp vision.
Types of Lenses Used for Astigmatism
The most common option for correcting astigmatism with contacts is the soft toric lens. These lenses are engineered with different powers in their vertical and horizontal orientations to match the eye’s irregular shape. Crucially, soft toric lenses include stabilization features, such as prism ballast or thin-thick zones, to keep the lens from rotating on the eye. If the lens rotates, the specialized corrective power will be misaligned, leading to blurry vision.
For individuals with high amounts of astigmatism or conditions like keratoconus, which causes a more irregular cornea shape, other options may be recommended. Rigid Gas Permeable (RGP) lenses are a common alternative because they maintain a perfectly spherical shape on the eye. The rigid structure of the RGP lens vaults over the irregular cornea, creating a smooth optical surface between the lens and the eye, which is filled with a layer of tears. Hybrid lenses combine the sharp vision of an RGP center with the comfort of a soft lens skirt, offering another option for complex cases.
The Essential Role of Lens Fitting
The fitting process for any astigmatism contact lens is significantly more involved than for standard spherical lenses. The eye care professional must first determine the magnitude of the astigmatism, known as the cylinder power, and the specific angle, or axis, at which the power must be oriented. This diagnostic step often involves instruments like a topographer to map the precise curvature of the cornea. The prescription for a toric lens is therefore more complex, requiring spherical power, cylinder power, and axis notation.
Once a trial lens is selected based on these measurements, it is placed on the eye and allowed to settle for several minutes. The eye care provider then assesses the lens’s fit, alignment, and movement using a slit lamp microscope. The primary goal is to ensure the stabilization features keep the lens in the exact orientation needed, preventing excessive rotation with blinks or eye movements. Multiple trial lenses are often tested across several visits to find the optimal combination of base curve, diameter, and stabilization mechanism that minimizes rotation and maximizes stable, sharp vision.
Managing Vision Stability and Comfort
Even after a successful fitting, the experience of wearing astigmatism contacts involves a unique set of considerations for the wearer. The specialized stabilization mechanisms in toric lenses are designed to keep the lens aligned, but a small degree of temporary rotation may still occur, especially during a hard blink. When the lens shifts, the corrective power is briefly misaligned with the eye’s axis, which can cause a momentary blurring or fluctuation of vision until the lens rotates back into its correct position.
Some wearers may also experience a difference in comfort compared to standard contacts, often related to the lens design. Toric lenses are frequently manufactured with thicker zones or weighted areas to aid in stabilization, which can sometimes lead to a feeling of greater lens awareness. Maintaining a consistent and healthy tear film is also important, as dryness can increase friction and cause the lens to move more frequently. If frequent, severe rotation or persistent discomfort is experienced, the wearer should return to their eye care professional for a potential adjustment in lens design or stabilization system.