Astigmatism is a common refractive error that occurs when the cornea or lens inside the eye is not perfectly spherical, instead possessing a shape similar to a football or a slice of a donut. This irregularity causes light to focus at two different points inside the eye, resulting in blurred or distorted vision at any distance. People with this condition who also wish to change or enhance their eye color can successfully use specialized vision correction known as colored toric contact lenses. They are available through prescription and require a precise fitting from an eye care professional to ensure both clear sight and a natural appearance.
How Colored Toric Lenses Maintain Stability
The technology behind colored toric lenses is complex because the lens must stay aligned with a specific orientation on the eye to correct the astigmatism. Standard contacts can rotate freely without affecting vision, but a toric lens must align with the cylinder and axis measurements specific to the wearer’s eye. Even a slight rotation of the lens out of position can cause vision to become blurred or fluctuate. Manufacturers use several stabilization technologies to prevent this unwanted movement.
One common method involves the use of prism ballast, where a section of the lens is made thicker or slightly heavier at the bottom. This increased mass takes advantage of gravity and the lower eyelid to keep the lens from rotating. Another approach utilizes thin-thick zones, also referred to as dynamic stabilization. This method relies on the interaction between the lens and the eyelids, using four stabilization zones to realign the lens quickly with every blink.
Stability is especially important for colored toric lenses because the colored pattern must remain positioned correctly over the iris. The color is manufactured to align with the clear central zone that sits over the pupil. If the lens rotates, the colored portion can shift, resulting in an unnatural appearance and potentially obstructing the pupil, which can affect vision, particularly in low light.
Available Color Options and Limitations
Colored contacts for astigmatism generally come in two main types of tints to achieve different cosmetic effects. Enhancement tints are translucent and are designed to intensify the wearer’s natural eye color, making them more suitable for people with lighter irises. Opaque tints completely cover the natural eye color with a solid, non-transparent layer of pigment, allowing people with dark eyes to achieve a significant color change.
Opaque color options are frequently featured in colored toric designs. This is partly because the opaque pigment layer can sometimes be incorporated into the lens in a way that contributes to the stability profile. The availability of colored toric lenses, however, is significantly more limited than that of clear toric or non-prescription colored contacts.
The manufacturing process for toric lenses is complicated and costly due to the vast number of power combinations required to account for sphere, cylinder, and axis. This complexity is compounded when adding color, resulting in fewer stock options for cylinder power and axis measurements. Standard colored toric lenses may only be available in a restricted range of axes, such as 180 degrees, and lower cylinder corrections, such as up to -1.25 diopters.
For those with high or complex prescriptions outside the standard range, custom-made colored toric lenses are an option. These custom lenses can accommodate a wider array of powers and colors but are considerably more expensive and may take several weeks or months to produce.
The Essential Fitting and Prescription Process
All contact lenses, including those worn purely for cosmetic reasons, are classified as medical devices and require a valid prescription from a licensed eye care professional. The fitting process for colored toric lenses is precise and requires more time than fitting standard spherical lenses. The eye doctor must first conduct a comprehensive eye examination to determine the exact sphere, cylinder, and axis measurements needed for clear vision.
Once the lens is applied, the doctor allows it to settle on the eye for several minutes to observe its alignment and rotational stability. They check the lens position to ensure the orientation marks are correctly aligned with the astigmatic axis. The practitioner then evaluates how quickly the lens returns to the correct position after a blink, often quantifying any rotation using a slit lamp.
It is necessary to be fitted with the exact brand and type of colored lens intended for purchase. The presence of the color pigment and the specific stabilization design of a colored toric lens can alter the way it fits and feels compared to a clear lens. A trial period allows the wearer and the doctor to confirm that the lens provides stable, clear vision, remains comfortable, and that the color placement is aesthetically acceptable before finalizing the prescription.