Learn about lens properties and characteristics
Contact lenses come in all sorts of varieties and possess all kinds of different properties. So, it might not be easy knowing exactly what's what. This short guide takes a look at the most common lens characteristics and their differences; this way, you can get an idea of what matters when you’re buying contact lenses. Of course, in case you have any further doubts or questions, don’t hesitate to consult your optician - optometrist or ophthalmologist. It's their job to figure out precisely what's right for you.
Lens material: hydrogel versus silicone-hydrogel
Hydrogel is an artificially created hydrophilic (water-binding) material. It’s the oldest material used for soft contact lenses and is often cheaper than silicone hydrogel. This material contains a large amount of water, and, thus, is bio-compatible. Hydrogel itself is not a very breathable material, thus oxygen is not able to easily penetrate through it. The oxygen molecules are transported through the hydrogel via the process of diffusion. To this day, hydrogel lenses are still very comfortable and well-tolerated, especially by those with sensitive eyes.
Silicone-hydrogel is the newest material in contact lens production. The hydrogel component helps ensure a decent water content, and the silicone provides very high oxygen permeability. This material was developed much later than hydrogel and tends to be a bit more expensive. Though most current silicone hydrogel lenses have a very good water content, this material is known for having far less water than hydrogel lenses, making them slightly more prone to deposits and drying out. On the other hand, the oxygen transfer is much higher, which helps reduce hypoxia-related symptoms. Because silicone-hydrogel lenses have such high levels of oxygen permeability, some varieties are approved for continuous wear.
When it comes to choosing which is better, the consensus is that silicone hydrogel has come to be far more advanced and performs better than hydrogel. However, hydrogel lenses are still preferred by many users and tend to be a better fit for some. Especially when it comes to lenses with a shorter replacement schedule, hydrogel is still very popular. In the end, it all depends on your eyes and your needs!
The importance of oxygen and water
Regarding contact lenses, both oxygen and water play a huge role in your eye health. A high water content ensures that the lenses feel comfortable, hydrated, and natural. A high oxygen permeability, on the other hand, ensures that your cornea will receive a lot of oxygen, which it needs to keep your eyes as healthy as possible. When it comes to choosing between a lot of water or a lot of oxygen – which brings us back to the choice between hydrogel or silicone-hydrogel – there really isn’t a right answer. It all depends on your needs and your eyes. Some users are able to perfectly tolerate lower oxygen lenses that have more water while others may need to opt for higher oxygen lenses. This will all become clear when you’re trying new lenses with your optician or eye doctor.
Extended-wear or continuous lenses
Contact lenses with a prolonged or continuous wearing schedule are ideal for lens wearers who want to fully enjoy the convenience and comfort of lenses without removing them overnight. These lenses are made from revolutionary silicone-hydrogel materials, which ensure six times greater oxygen permeability than traditional lenses. This makes the lenses suitable for overnight wear. However, users must always consult an ophthalmologist before beginning this type of wearing regimen to avoid health risks and complications. This method of wearing lenses is not suited for everyone!
Types of vision correction
Contacts have been designed to correct all sorts of vision problems. Each issue requires a certain type of lens. Below, we’ll take a look at the main types of contact lenses and what makes them different. In case your optician or eye doctor did not mention that you have any sort of special needs, they will always indicate it on your prescription.
Spherical versus aspherical lenses
Spheric contact lenses are contact lenses that offer basic correction. They have the same lens power throughout the entire optical part of the lens to correct myopia (nearsightedness) or hyperopia (farsightedness). This type of lens will provide a stable correction. All brands of spheric lenses are available in a wide range of positive and negative dioptres.
Within the spheric lenses category, there is a further distinction between spherical and aspherical lenses. Spherical lenses are the most standard ones and offer normal vision correction. However, their spherical outer surface shape does not always properly refract all light rays. This means that slight distortions or visual aberrations may occur along the edge of the lens. Aspherical lenses possess an outer surface that flattens and changes shape along the edges. This shape is able to better and more naturally refract light, causing your vision to be clearer and sharper. Aspherical lenses are even able to correct low forms of astigmatism. Though spherical lenses still perform very well, aspherical lenses tend to always perform better, especially in lower light conditions.
Toric contact lenses are intended for the correction of astigmatism. Astigmatism is a common condition that's usually caused by an irregular curvature of the cornea. That can be corrected with the help of aspherical toric contact lenses. Besides power, base curve, and diameter, toric contact lenses also have an axis (AX) and cylindrical power (CYL) as special parameters necessary to correct astigmatism. This means that you will have to carefully fill out two additional values when ordering lenses. Having trouble finding your exact values? Consult with your optician or ophthalmologist before buying any values or parameters that deviate from your prescription.
Multifocal contact lenses (also called bifocal or varifocal contact lenses) are intended for the correction of presbyopia, an age-related issue that is caused by the loss of elasticity of the lens in the eye and often occurs in people over 40 years of age. They are comparable to spectacles with bifocals or progressive lenses because they have multiple focal points. Multifocal lenses allow clear vision at all distances and the ability to see comfortably without glasses. Multifocal lenses can also help relieve some health-related problems such as headaches, dizziness, or eye strain. They are often characterised by an additional ADD value.
Contact lenses always have a certain replacements schedule, with the most common ones being daily - bi-weekly or monthly. A replacement schedule indicates how long you can actually wear a lens. A daily lens can only be worn for one day, a bi-weekly one for 14 days, and a monthly one for 30 days. Disposable daily lenses, biweekly lenses, and monthly lenses are not designed to outlast their specified wearing period. Read more about the risks of overwearing lenses here. And, if lenses are not specifically designed for extended or continuous wear, you should never sleep in them!
Additional lens properties
Some lenses might even have additional features and characteristics. All of those features were developed to enhance the contact lenses and make them more convenient, comfortable, and up-to-date. However, some of these might not be a good fit for you. So, be sure to always first get trial lenses from your optician or eye doctor.
Contact lenses may contain a UV filter. This filter will help block certain harmful UV (ultraviolet) rays and keep your eyes protected from the sun. That is to say, at least part of your eyes: your cornea. You should always keep in mind that a contact lens doesn't cover the complete eye. In order to properly and fully keep your eyes safe from the sun, you will need a quality pair of sunglasses. Lenses with a UV filter are a great way to further protect your vision, but they can never replace sunglasses when it comes to total protection.
Clear contact lenses are not always easy to see or handle. In order to make them more visible, some manufacturers have added a very light and, often, blue handling colour to their lenses. This helps you to easily spot them in their blisters or cases and helps you to properly see them during insertion or cleaning. This tint is in no way intended to change your eye colour and is barely, if at all, visible while wearing the lenses. It’s simply meant to make your life easier when handling the lenses.
Reverse side indicator
It can be tricky – when inserting lenses – to notice whether your lens is backwards or not. Wearing a lens backwards can hurt and cause blurry vision, meaning you’ll have to take it out and start all over again. This kind of fumbling could easily also lead to red and irritated eyes. So, some manufacturers have devised a solution: a reverse side indicator. These are tiny numbers or letters engraved near the edge of the lens that’ll show you if the lens is inside out or not. If the engraving reads correctly, you’re good to go. If not, then your lens needs to be flipped before you place it onto your eye.
Sodium hyaluronate (Hyaluronic acid) is a natural component of living organisms. It can be found in body fluids, cartilage, skin, the vitreous, and, for babies, the umbilical cord. As it is natural to the human body, lenses enriched with this material are well-adjusted and comfortable to wear. The contact lens care industry uses sodium hyaluronate as a lubricating agent in eye drops and contact lens solutions. Due to its properties, it is excellent for supplying eyes and contact lenses with the necessary moisture to avoid any irritation. Sodium hyaluronate also promotes eye cell regeneration.