Have you ever gazed at a light and noticed it looked more like a blurry starburst rather than a clear dot? Or maybe you’ve had eyeglasses for a while and heard the term “astigmatism” thrown around during your optometrist visits. Either way, you’re probably wondering about a solution to this problem, and the answer might be simpler than you think: toric contact lenses.
In this post, we’ll demystify astigmatism, explore what toric contact lenses are, and break down how they work to rectify this particular vision concern.
If you’re curious about how you can achieve sharper vision with contacts, even with astigmatism, read on.
What Is Astigmatism?
Astigmatism is a refractive error, similar in some ways to nearsightedness and farsightedness. However, rather than being caused by the length of the eye, astigmatism is the result of an irregular shape of the cornea—the clear, front part of the eye—or sometimes the curvature of the lens inside the eye. Ideally, the cornea should have a symmetrical round shape, much like a basketball. But in cases of astigmatism, the cornea tends to be more oblong, like a football. This irregular shape causes light to be refracted unevenly as it enters the eye, leading to blurred or distorted vision.
Signs and symptoms of astigmatism may include:
- Blurred or distorted vision at all distances
- Eye discomfort or strain
- Difficulty seeing clearly at night
- Frequent squinting
An analogy that is commonly used to explain astigmatism is to compare the shape of your cornea to a football or a basketball. Imagine trying to bounce a football compared to a basketball. While the basketball bounces predictably straight up and down due to its symmetrical shape, the football, with its elongated shape, can bounce in unpredictable directions. Similarly, astigmatism disrupts the predictable path of light into our eyes, making things appear blurry or distorted. Instead of a uniform curve like a basketball (or baseball), the eye’s surface with astigmatism is more uneven, like a football.
How Toric Soft Contacts Correct Astigmatism
Toric contact lenses are specially designed to address the uneven curvature of the eye caused by astigmatism. Unlike regular contacts that have a singular power throughout the lens, toric lenses have two different powers. One corrects for astigmatism, and the other corrects for nearsightedness or farsightedness, if present. The unique design of toric lenses enables them to realign the light entering the eye, ensuring it focuses on the retina correctly. This correction gives those with astigmatism a clearer, sharper vision.
One of the challenges of correcting astigmatism with contact lenses is ensuring the lens remains stable on the eye and doesn’t rotate, which would cause blurred vision. To address this, toric lenses are weighted slightly at the bottom. This design ensures they maintain the correct orientation and alignment, offering consistent visual clarity throughout the day. The weight is so subtle that wearers typically don’t notice it, but it’s essential for delivering the corrective power exactly where it’s needed.
At a glance, toric contact lenses might seem similar to standard spherical lenses, but there are crucial differences between the two. While spherical lenses have the same lens power throughout, offering a single correction for vision (either nearsightedness or farsightedness), toric lenses provide dual corrective powers to accommodate both astigmatism and any other refractive error. The added stability feature in toric lenses, which keeps them from rotating on the eye, also sets them apart from the freely rotating spherical lenses.
So, while spherical lenses focus on straightforward refractive corrections, toric lenses are tailored to the unique needs of astigmatic eyes. And because they have a more sophisticated design, toric lenses are more expensive to manufacture and cost more than spherical lenses.
How Rigid Gas Permeable (RGP) Contacts Correct Astigmatism
Rigid gas permeable (RGP) contacts are durable, rigid lenses made of materials that allow oxygen to pass through them. This oxygen permeability offers a higher degree of clarity and can be healthier for the eyes than some traditional soft lenses. RGP lenses retain their shape on the eye, as opposed to conforming to the shape of the wearer’s eye like soft lenses. This characteristic is particularly beneficial for correcting astigmatism, as the lens effectively acts as a new, regularly shaped front surface for the eye.
When an RGP contact lens is worn on an eye that has mild to moderate astigmatism, the space between the (spherical) back surface of the contact lens and the (astigmatic) front surface of the cornea is filled with tears. This layer of tears is shaped in such a way that it becomes, in effect, a lens that fully corrects the astigmatism of the eye.
The “tear lens” behind the RGP contact lens is unaffected by lens rotation. Therefore, the only lens power required in the contact lens is the power needed to correct any nearsightedness or farsightedness that exists along with the astigmatism.
In cases of moderate to severe astigmatism, a standard RGP contact lens may be uncomfortable or unstable on the eye because the shape of the cornea is so irregular that the contact lens doesn’t center properly on the eye and moves (or “rocks”) too much during blinks. In these cases, a toric RGP contact lens may be used.
Soft Toric Contacts vs. RGP Contacts for Astigmatism
While toric soft contacts are a popular choice for many with astigmatism, there are instances where RGP lenses might be more suitable.
For individuals with high or irregular astigmatism, RGPs can offer sharper vision because they maintain their rigid shape, whereas soft lenses might not fully correct the irregularity.
Moreover, people with certain eye conditions, like keratoconus, where the cornea becomes cone-shaped, might find better vision correction with RGP lenses. RGPs are also known to resist deposits, are less likely to harbor bacteria than soft lenses, and can be custom-made for a precise fit, making them a preferred choice for those seeking optimal visual clarity.
But while RGP lenses offer several advantages over soft toric contacts, they come with a few drawbacks as well. One of the most common challenges for new wearers is the initial comfort. Because RGP lenses are rigid, they may not be as immediately comfortable as soft lenses, and there can be an adjustment period.
Cost can also be a factor. Toric RGP lenses have a more sophisticated design, so they are more expensive to manufacture. As a result, they cost more than standard RGP contact lenses.
Additionally, the long replacement schedule of RGP lenses can lead to users neglecting routine care or wearing them beyond their recommended lifespan, which could pose eye health risks.
Astigmatism is a common yet often misunderstood eye condition. But by exploring its nuances, we hope we’ve shed light on its nature and symptoms, as well as the corrective options available for this condition beyond eyeglasses.
If you have astigmatism, your eye doctor will help you determine the contact lens best suited for your particular needs.