Astigmatism affects a significant portion of Singapore's population. In fact, research from the Singapore Epidemiology of Eye Disease Study (2013) found that 58.8% of adults over the age of 40 have some degree of astigmatism. This issue lies in the eye's geometry: while a healthy eye is spherical, astigmatism involves an irregular corneal shape that scatters light across multiple focal points, which is an aspect that a single-power lens cannot compensate for.
For contact lens wearers with astigmatism, toric lenses are designed specifically to address this.
Unlike regular contact lenses, toric contact lenses feature different refractive powers across the vertical and horizontal planes of the contact lens. These varying powers shift gradually across the lens surface, allowing the lens to counteract the way an astigmatic eye bends light unevenly.
But are they the right option for your astigmatism?
What Are Toric Contact Lenses?
Standard contact lenses feature a spherical surface with uniform curvature. Given this structure, it has the same refractive power at every point across its surface. This uniform design, much like a section sliced from the side of a ball, corrects myopia or hyperopia effectively because those refractive errors are consistent across the eye.
So, what is the difference between toric and regular lenses?
The term 'toric' comes from 'torus', a geometric shape resembling a doughnut. A cross-section of a torus reveals two distinct curves: one with a shallower arc and one with a steeper arc, running perpendicular to each other. In practical terms, this means that the toric contact lens is thicker along one meridian and thinner along another.
This structure gives toric lenses varying optical powers along different axes of the lens. This means that while a spherical lens refracts light the same way regardless of orientation, a toric lens, by contrast, refracts light differently depending on where on the lens surface light passes through. This is what allows a toric lens to match the uneven optical demands of an astigmatic eye.
What Does a Toric Lens Do?: How It Corrects Astigmatism
According to SingHealth, the cornea in an astigmatic eye is oval-shaped rather than spherical, which causes problems in focusing light as it enters the eye. Rather than converging at a single point on the retina, light focuses on multiple focal points, resulting in blurred or distorted vision.
While toric lenses do not treat this condition, they work to correct the vision problems it causes by compensating for the cornea's uneven curvature. Given its aforementioned unique design, when positioned correctly, toric lenses redirect incoming light so that it converges on a single focal point on the retina, producing clear vision.
And because the steeper curve of the toric lenses needs to align with the flatter meridian of the cornea for this to be possible, orientation on the eye is critical. Unlike spherical lenses, which function the same way regardless of how they sit, toric lenses must remain at a specific angle to deliver the intended correction. If the lens rotates out of position, the corrective powers no longer align with the eye's astigmatism axis, and vision becomes blurry.
Why Proper Fitting is Critical for Toric Lenses
Given that even minor rotation affects visual clarity, how do toric lenses stay in place?
Design Features That Keep Toric Lenses in Place
Manufacturers design toric contact lenses with built-in stabilisation features to help the lenses maintain their position.
- Thin-thick zone design: The lens varies in thickness across different areas. The eyelids interact with these zones during blinking, naturally guiding the lens back into position if it shifts.
- Prism ballasting: The lens is designed to be slightly thicker below the lower eyelid. This added weight is influenced by gravity, which helps keep the lens oriented correctly throughout the day.
- Lens truncation: The bottom edge of the lens is slightly flattened. This flat section rests against the lower eyelid, reducing the likelihood of the lens spinning out of alignment.
The specific stabilisation method used depends on the lens brand and the wearer's individual eye characteristics, which is why a professional fitting is necessary to determine which design works for each person.
Different Types of Toric Contact Lenses
Toric lenses come in two main material categories: soft lenses and rigid gas-permeable (RGP) lenses. Each has characteristics that may suit different wearers depending on comfort preferences, lifestyle, and the degree of astigmatism.
1. Soft Toric Contact Lenses
Soft toric lenses are made from flexible hydrogel or silicone hydrogel materials that conform to the shape of the eye. This flexibility makes them comfortable for most wearers from the outset. And because these soft lenses are pliable, the stabilisation features described above play a significant role in keeping them correctly oriented.
They are also available in daily, fortnightly, and monthly disposable options, allowing wearers to choose a replacement schedule that fits their routine.
2. Rigid Gas Permeable (RGP) Toric Lenses
RGP toric lenses are made from oxygen-permeable silicone polymers that hold their shape on the eye rather than moulding to the corneal surface. This firmness can provide sharper vision for some individuals, particularly those with higher degrees of astigmatism, because the lens maintains a consistent optical surface.
The trade-off is comfort.
RGP lenses typically require a longer adaptation period as new wearers may experience awareness of the lens on the eye for several days or weeks before becoming accustomed to the sensation. RGP lenses also tend to have a longer lifespan than soft lenses, as they do not need to be replaced as frequently.
How to Know if You Need Toric Contact Lenses
Does your current vision still feel slightly "off" or blurry, even with standard lenses? Not everyone with astigmatism requires toric lenses, though.
Signs You May Have Astigmatism
Several symptoms may indicate the presence of astigmatism:
- Persistent blurry vision, even when wearing regular contact lenses or glasses
- Difficulty seeing clearly at night, particularly when driving
- Distorted shapes or objects appearing stretched
- Streaking or halos around lights
- Eye strain after prolonged visual tasks
If you are experiencing any of these signs while wearing spherical contact lenses, it may be worth discussing toric options with your optometrist. A comprehensive eye checkup can confirm whether astigmatism is present, determine its severity, and establish whether toric lenses would provide clearer correction than your current lenses.
Why a Professional Contact Lens Fitting Matters
As covered earlier, toric lenses must sit at a specific orientation to function correctly. As such, purchasing contact lenses without a professional fitting poses risks, particularly for those with astigmatism. This is because off-the-shelf lenses do not account for individual variations in:
- Corneal shape and curvature
- Astigmatism axis and degree
- Tear film characteristics
- Eyelid interaction with the lens
Moreover, an ill-fitting lens can cause discomfort, dryness, and inconsistent vision. More seriously, lenses that move excessively or do not move on the eye increase the risk of corneal abrasions or infections.
A professional contact lens fitting involves detailed measurements of the eye's surface and a trial period with specific lenses. The optometrist assesses how the lens sits, how it moves with blinking, and whether the visual correction is accurate. Adjustments to lens parameters can then be made to ensure a proper fit.
Have Your Eyes Checked for Astigmatism at Kacee Eye Care
If you suspect you have astigmatism or your current contact lenses are not delivering clear vision, an eye checkup in Singapore can provide answers. At Kacee Eye Care, we conduct comprehensive assessments to evaluate refractive errors, including astigmatism. Kacee Eye Care also offers other vision correction options, including Ortho-K lenses for individuals who prefer overnight wear.
Book an appointment to have your eyes assessed and explore the contact lens options that may support your visual needs.