In the world of vision correction, contact lenses have become an essential tool for many people. They offer an alternative to glasses, providing both convenience and comfort.
But not all contact lenses are equal. The key to their differences lies in the materials used to make them.
In this handy guide, we will dive into the many different kinds of contact lens materials, exploring their features and potential drawbacks.
1. Rigid Gas-Permeable (RGP) Lenses
Rigid gas-permeable (RGP) lenses are made from a combination of silicone and fluoropolymers. This unique material composition makes the lenses hard, yet they still allow oxygen to permeate. Like most other cells in our bodies, our eyes need oxygen to stay healthy.
Advantages:
- Superior visual clarity – One of the standout features of RGP lenses is the high-quality vision they offer. Their rigidity means they maintain their shape even when you blink, preventing the distortion that can sometimes happen with soft lenses.
- Support optimal eye health – The permeability of RGP lenses means they allow more oxygen to reach the cornea than standard soft lenses. This can help reduce the risk of contact lens-related complications, such as corneal oxygen deficiency.
- Durability – With proper care, RGP lenses can last considerably longer than soft lenses, often up to a year or more. Their rigid nature means they are less prone to tearing or damage.
- Cost-effective in the long run – Due to their extended lifespan, many wearers may find RGP lenses to be more economical over time when compared to regularly replaced soft lenses.
- Ideal for special eye needs – RGP lenses are particularly beneficial for wearers with keratoconus and high levels of astigmatism than standard soft lenses. They offer clear vision and can be customized to fit irregularly shaped corneas.
Disadvantages:
- Initial discomfort – RGP lenses can take some time for users to get used to. They can initially feel more uncomfortable or foreign than soft lenses.
- Needs consistent wear – Extended breaks can make re-adaptation to RGP lenses challenging. To maintain comfort, it’s advised to wear RGP lenses consistently.
- High maintenance – RGP lenses should be cleaned daily with the recommended cleaning solution and stored in a clean case with fresh solution.
2. Soft Lenses
Soft contact lenses are primarily composed of gel-like, water-containing plastics known as hydrogels. Developed in the 1970s, hydrogels revolutionized the contact lens industry by providing a more flexible and comfortable alternative to rigid lenses. The water content in these lenses can vary, which influences their flexibility and oxygen permeability.
Some soft contact lenses are made of silicone hydrogels, which allow even greater levels of oxygen to reach the cornea. This increased oxygen permeability means that wearers can safely use these silicone hydrogel lenses for extended periods. The risk of contact lens-related complications is also reduced with silicone hydrogel lenses.
Advantages:
- Immediate comfort – Soft lenses are more comfortable right from the start than RGP lenses. The flexibility of soft lenses allows them to easily conform to the eye’s shape, making them especially user-friendly for first-time wearers.
- Versatility – Soft lenses come in a variety of designs to suit different vision needs, including spherical (for myopia or hyperopia), toric (for astigmatism), multifocal (for presbyopia), and even cosmetic (to change eye color).
- Available in various modalities – Soft lenses are available in multiple replacement schedules, including daily, bi-weekly, and monthly options, catering to different lifestyles and preferences.
Disadvantages:
- Can dry out – Soft lenses may become less comfortable in dry environments or during prolonged screen time.
- May not be ideal for certain prescriptions – Soft lenses may not provide as crisp a vision as RGP lenses for high levels of astigmatism and other eye conditions.
- Lower oxygen permeability – Standard hydrogel soft lenses may not allow as much oxygen to pass through to the cornea as some other lens types.
- High maintenance – With the exception of daily disposables, soft lenses require a consistent cleaning routine to prevent deposit buildup and potential eye infections.
- Fragile – Due to their pliability, soft lenses can be more prone to tearing or damage, especially during insertion or removal.
Hydrogel vs. Silicone Hydrogel: Which Is Better?
Hydrogel contact lenses, introduced in the 1960s, are primarily made from hydrophilic polymers. The high water content of these lenses provides the eyes with adequate oxygen through direct oxygen diffusion from the atmosphere. This ensures that the eyes remain comfortable during wear. But because of their softer and more water-rich nature, they may be prone to deposits, can dehydrate in certain environments, and typically allow less oxygen to the cornea compared to silicone hydrogel lenses.
Silicone hydrogel lenses are a more recent advancement in contact lens technology. Made available in the late 1990s, these lenses incorporate silicone into the material, enabling them to transmit more oxygen to the cornea than traditional hydrogel lenses and reduce the risk of hypoxia-related complications. They also tend to retain moisture better and are more resistant to protein and lipid deposits. However, some wearers may experience initial discomfort due to the slightly different material properties.
While both hydrogel and silicone hydrogel lenses are designed to improve vision and comfort, the latter offers superior oxygen permeability, which promotes better eye health. Silicone hydrogel lenses also have better deposit resistance and moisture retention properties. That said, there is no true “best” contact lens material. Every wearer has unique eye health needs, lifestyles, and preferences, so what’s best for you may not be best for other lens wearers and vice versa.
3. Hybrid Lenses
Hybrid contact lenses merge the best of both worlds. They have a central RGP zone surrounded by a soft peripheral ring made of either hydrogel or silicone hydrogel. This design aims to offer the crisp vision of RGP lenses combined with the comfort of soft lenses. For wearers looking for the crisp vision of rigid lenses without sacrificing comfort, hybrid lenses can be an excellent choice.
Advantages:
- Visual clarity – Similar to RGPs, the central rigid zone of a hybrid lens provides superior optical clarity. As such, hybrid lenses are especially beneficial for wearers with irregular corneal conditions, like astigmatism and keratoconus.
- Comfort – The soft outer skirt of a hybrid lens ensures a snug fit, reducing the likelihood of the lens dislodging from the eye. This gives wearers the comfort typical of standard soft lenses.
- Centration – The soft skirt of a hybrid lens helps keep its central RGP zone centered on the eye. This consistent centration is crucial for conditions like presbyopia, where the precise positioning of the corrective zone on the lens is essential for optimal vision.
- Reduced lens awareness – The transitional zone between the rigid center and the soft skirt of a hybrid lens is designed to be very smooth, which reduces the sensation of the lens on the eye.
Disadvantages:
- Difficult fitting – Hybrid lenses can be more difficult to fit than other lens types.
- High maintenance – Like RGP lenses, hybrid lenses require a meticulous lens care regimen to maintain their shape and function.
- High cost – Because hybrid lenses are specialized, they can be more expensive than traditional soft or RGP lenses.
4. PMMA (Polymethyl methacrylate) Lenses
PMMA lenses are made of a transparent thermoplastic called polymethyl methacrylate. Also known as Plexiglas or acrylic, this material revolutionized the contact lens industry in the 1940s, so much so that PMMA was once considered the best material for contact lenses.
However, the introduction of more breathable lenses, especially RGP lenses, led to a decline in the popularity of PMMA lenses.
Today, PMMA lenses are rarely prescribed and are mainly used in specific cases where other materials may not be suitable. But while they have been largely replaced, the PMMA material itself continue to be vital in medical and optical applications.
Considerations When Choosing Contact Lens Materials
Selecting the right contact lens material is a crucial decision that can significantly impact your eye health, comfort, and overall experience. Below are factors that your eye care professional (ECP) will likely consider when determining which material is best for you:
1. Oxygen Permeability
The cornea requires a constant supply of oxygen. Depriving the eye of necessary oxygen can lead to complications, including corneal neovascularization, where blood vessels grow into the cornea due to oxygen deprivation. Lenses that allow more oxygen to pass through, like silicone hydrogel and RGP lenses, can generally be worn for longer periods.
2. Vision Correction Needs
If you have a high prescription or special eye care needs, certain materials or lens designs might be more suitable.
3. Comfort
This is subjective and can vary from person to person. Some wearers might find RGP lenses uncomfortable but appreciate their sharp vision, while others prioritize the immediate comfort of soft lenses. If you have sensitive eyes or dryness issues, certain materials might also be more suitable for you.
4. Lifestyle
Whether you plan to wear your lenses daily, occasionally, or overnight can dictate the best material for you. Extended wear lenses require materials with high oxygen permeability (like silicone hydrogel), while daily disposable lenses might require a more water-loving material, like hydrogels.
5. Cost
Certain lens materials or specialized lenses might come with a higher price tag. It’s always a good idea to talk to your ECP about any budget considerations you have, as those may play a role in their recommendation.
6. Past Experience
If you’ve worn contact lenses before and had a good or bad experience with a particular material, this can guide your ECP’s recommendation as well. But as lens technology is continually advancing, being open to trying newer materials can be beneficial.
Conclusion
The world of contact lenses is diverse, with various materials catering to different needs and preferences. Understanding these materials, their benefits, and potential challenges can guide you towards the right choice for your eyes. Always consult with an ECP to find the best fit and material for your specific vision needs and lifestyle.
This information is intended as a resource, not medical advice. Be sure to consult with your ECP to determine your specific needs.
