The lenses of a pair of glasses are developed based on three factors:
- the choice of materials, which determines the thickness, weight and safety;
- the treatment, which impacts the permeability of light and the simplicity of cleaning the lenses; and
- the design, which ensures the vision correction.
The choice of lenses usually starts with the material and depends on the correction of your sight and your activities. For example, if you have a certain hobby or participate in sports, these can require a certain type of material. Your budget can also play a role in this.
Lenses are primarily made of plastic (organic lenses) or glass (mineral lenses):
Lenses made of plastic are almost three times as light as ones made of glass and do not break as quickly. They can scratch faster, but with a proper hard coating (also called an anti-scratch layer) and careful treatment, scratches can be easily avoided.
Lenses made of mineral glass are more scratch-resistant and attract less dirt. Because of this, they are never dull and keep their sharpness and clarity for longer. They are also cheaper than organic lenses. However, lenses made of glass are rarely sold. After all, they are much heavier and more breakable, which makes them more dangerous if you’re in an accident.
The thickness of the lenses is then dependent upon the refractive index. The higher the refractive index, the thinner the lens:
- Slight corrections of +2 or -2: standard lenses with a refractive index of 1.5 are sufficient.
- Corrections between +2 and +4 or -2 and -4: you are better off choosing lenses with a refractive index of 1.6. If safety and shock protection (e.g. during certain sports) are important to you, we also recommend (organic) lenses with a refractive index of 1.6. The same applies to rimless and nylor glasses.
- Corrections higher than +4 or -4: you are better off with extra thin lenses with a refractive index of 1.67 or more.
We carefully consider the type of lens and the refractive index, taking the size of your frames, your interpupillary distance, the shape of your lenses and your daily activities into account.
The front and back sides of the lenses can be treated in a specific manner so as to increase the viewing comfort and better protect the lens. For example, lenses can be made non-reflective, and provided with scratch-resistant and/or water and dirt-repellent layers.
Lenses are made non-reflective to prevent reflections from disturbing your vision. This gives you clear vision and better sight with more contrast. It also looks nicer and your eyes don’t get tired as quickly. Moreover, it’s much safer, especially when driving at night. Your vision is less sharp when you’re wearing glasses with reflective lenses. After all, light reflects off the lens, which means it doesn’t get through to your eyes. This is more noticeable at night or in the dark. Non-reflective lenses are susceptible to grease and dirt. We will be happy to suggest the right option for you, depending on your professional and private activities.
You can also opt for a coating that neutralises blue light. Blue light is a spectrum of daylight that helps keep us awake. But in our contemporary digital era, our computers, TVs, smartphones and tablets also emit a great deal of blue light. This profusion of blue light can really exhaust your eyes. Too much exposure can even lead to strain and insomnia. This coating neutralises blue light, which means that your eyes don’t get tired as quickly.
If you are outside a lot, we recommend getting lenses with a UV filter. UV rays can cause inflammation of the cornea, or even cataracts in the long term.
We always recommend a substantial hardener to make your lenses even more scratch-resistant. After all, plastic isn’t as hard as glass, which means that your lenses could become dull and scratched after time. This is not only aesthetically unpleasant, it also decreases the sharpness and clarity of your vision. Despite this anti-scratch layer, you still need to treat your glasses well. Even mineral lenses can scratch or become dull if they aren’t treated carefully.
Water and dirt-repellent layers
A dirt-repellent and anti-static layer ensures that your lenses attract less dirt and are easier to clean, which is definitely a benefit of having non-reflective lenses. Rainwater slides off easily too.
Firstly, the lenses of your glasses can either be spherical or aspheric. Spherical lenses are rounded, after the traditional shape of a lens. Lenses are aspheric as from the point where they are no longer rounded. These can then be polished in various ways. The lenses in most glasses are aspheric because this offers a better optical quality, but primarily because they are more aesthetically pleasant, the lenses look “flatter” or “more level”, and so appear thinner.
The design choice for your lenses depends on the type of correction that you require (and your activities).
- Nearsightedness: This is also referred to as myopia. You have difficulty seeing distant objects clearly. You need negative lenses.
- Farsightedness: In this case, we use the term hyperopia. You have difficulty reading and focusing on objects that are up close. This can be corrected with positive lenses.
- Astigmatism: The cornea of a “normal” eye will have a symmetrically round shape. Sometimes, however, there is a defect in the optical mechanism of the eye, causing the shape to be irregular. This causes vision to be blurred or distorted to some degree in certain axial directions. The most prevalent type is corneal astigmatism. In this case, the outer cornea is more oval rather than perfectly round. An oval lens naturally results in a less clear image. This image will fall perfectly on the retina in a specific axial direction, while falling just in front or behind of it from another axial direction. Astigmatism can occur on its own as well as in combination with nearsightedness or farsightedness.
- Age-related farsightedness: This is also referred to as presbyopia. A normal eye is usually focused at infinity when at rest. The eye must make adjustments to focus sharply on objects that are less than 6 metres away (optical infinity). As you grow older (usually starting in your 40s), this ability decreases due to the reduction in the elasticity of your eye’s lens. You’ll need reading glasses in this case.
Unifocal lenses have only one strength: they correct either nearsightedness or farsightedness, as well as astigmatism.
Multifocal lenses allow you to see objects that are both distant and close by sharply, as well as seeing everything in between clearly. They are also called progressive lenses. If you are nearsighted as well as needing reading glasses, then it is best to choose a pair of multifocal glasses. Multifocal glasses have gotten rid of abrupt changes when moving from distant objects to objects within reading distance and allow for a smooth transition. This wasn’t always the case, as with bifocals, which are now rarely sold.
Active lenses are intended for eyes that are constantly being worked hard. Your eyes are working all day long in principle, whether you’re working, playing or just resting at home. Your eyes must constantly adjust to create a sharp image at any distance. Then you add in the almost permanent use of laptops, smartphones, driving, etc. Digital technology is a part of our daily lives; we always want to be in touch and up-to-date. So it’s no surprise that your eyes feel like they’re burning, irritated or tired at the end of the day. After all, you’re making constant, unusual demands of your eyes. People as young as 20 as well as people 40 years and older are starting to develop presbyopia and can be helped with this type of lens.
Computer lenses or “indoor” lenses are specially developed for distances that are both close and far away. If you are working behind a computer all day, then you are constantly changing your viewing distances, from your screen to your keyboard, to your paperwork to objects in your direct vicinity. You unconsciously look for the correct distance to be able to see things and work. Without specially adjusted lenses, this can lead to irritation of the eye, making them red and tired, as well as neck pains and other complaints. The viewing distance and reading distance of reading glasses and multifocal lenses are not aligned for looking at a screen right in front of you. Computer lenses correct your eyes for short and mid-range distances, which means your vision is sharp at these distances while giving you a wider reading range. This requires a lot less effort from your eyes.
Our lens manufacturers
Claeyssens Optic works with different lens manufacturers daily due to our high business volume. This is a major advantage for our customers because we know where to get practically every type of lens. Each manufacturer has its speciality. We prefer to work with the best brands on the market, including BBGR, De Ceunynck, Essilor, Hoya, Nikon, Rodenstock, Seiko and Zeiss. Together with you, Claeyssens Optic determines the best lenses, brand, material, width, improvements and design for your profile.