People with astigmatism can wear contact lenses. Astigmatism is a common condition where the eye’s front surface (cornea or lens) is curved imperfectly, shaped more like a football than a baseball. This irregularity causes light to focus on multiple points instead of a single point on the retina, resulting in blurred or distorted vision. Specialized contact lenses are required to counteract this uneven curvature and provide clear focus.
The Specialized Solution: Toric Lenses
The primary technology designed to correct astigmatism is the toric lens. Unlike a standard spherical contact lens, which has the same corrective power across the surface, a toric lens features two different powers in one lens. This design accounts for the varying degrees of curvature in an astigmatic eye, ensuring light is refracted correctly onto the retina.
Toric lenses require rotational stability; they must stay oriented in a precise position to align the corrective power with the eye’s irregular curvature. Without this stability, the lens would rotate with every blink or eye movement, causing vision to fluctuate and blur. Manufacturers employ engineering techniques to achieve this consistent alignment.
One common stabilization method is prism ballasting, where the bottom of the lens is made slightly thicker or heavier. This weighted zone uses gravity and the pressure of the lower eyelid to guide the lens back to its intended position after a blink. Another technique is dynamic stabilization, which uses thin and thick zones on the lens periphery that interact with the eyelids during blinking to quickly reorient the lens.
Types of Astigmatism Contacts
Correction for astigmatism is available across several different lens materials, each suited for varying degrees of the condition. Soft toric lenses are the most frequently prescribed option, offering comfort and ease of adaptation for mild to moderate astigmatism. These lenses are made from flexible hydrogel or silicone hydrogel materials and utilize stabilization features to maintain alignment.
For individuals with higher degrees of astigmatism or irregular corneal shapes, rigid gas permeable (RGP) lenses are often recommended. RGP lenses are smaller and firm, retaining their spherical shape instead of conforming to the corneal irregularity. This rigid structure creates a smooth optical surface over the eye, which helps neutralize the astigmatism and provides sharp vision.
A third option is the hybrid lens, which attempts to combine the features of both materials. Hybrid contacts feature a rigid gas permeable center, providing the clear visual acuity of RGP lenses, surrounded by a soft hydrogel or silicone hydrogel skirt. This combination offers superior vision correction from a firm lens with the increased comfort of a soft peripheral edge.
The Fitting and Adjustment Process
Fitting a contact lens for astigmatism is a more involved procedure than a standard contact lens fitting due to the need for precise alignment. The process begins with a comprehensive eye exam that includes specialized measurements of the eye’s curvature. The eye care professional may use corneal topography, a three-dimensional mapping tool, to accurately measure the precise shape and irregularities of the corneal surface.
The prescription for astigmatism requires three specific measurements: a sphere value for nearsightedness or farsightedness, a cylinder value to quantify the degree of astigmatism, and an axis value that indicates the precise orientation of the astigmatism on the cornea, measured in degrees from 0 to 180. This axis measurement is the most important factor for toric lenses, as the lens’s corrective power must align perfectly with this meridian.
After selecting an appropriate trial lens, the practitioner will observe the lens on the eye for several minutes to check its stability and centration. They assess how much the lens rotates after a blink and use subtle laser etchings or scribe marks on the lens periphery to objectively measure this rotation. If the lens rotates more than a small amount, the prescription needs adjustment to compensate for the rotation, or a different lens design may be necessary.
Patients should anticipate a trial period and potential follow-up appointments, as finding the optimal fit for a toric lens can take time and patience. It is common for vision to feel slightly unstable during the initial adjustment phase, especially with head tilts or quick eye movements. This meticulous fitting process is necessary to ensure the lens provides consistently clear and comfortable vision by keeping the specialized optics in the correct alignment.