Choosing the right glasses lenses is crucial as the lenses you choose will influence your appearance, comfort, vision and safety.
People often overlook their choices of lenses for glasses. However, it is important to carefully consider the lens material, designs and coatings.
No matter what prescription lenses you need, it is important to choose the best design for your needs. You should consider whether you're short-sighted, long-sighted or have astigmatism.
- Prescriptions from 0 to -2.50
- Prescriptions from -2.75 to -4.25
- Prescriptions from -4.50 to -6.00
- Prescriptions over -6.00
- Prescriptions from 0 to +2.00
- Prescriptions from +2.25 to +4.00
- Prescriptions from +4.25 to +6.00
- Prescriptions over +6.00
Glass lenses were the only choice available when vision correction first came about.
While they can offer exceptional clarity of vision, they are also extremely heavy and carry the risk of breaking. Both these factors pose a serious threat to your eyes. Glass lenses are no longer a common choice for this exact reason.
The first plastic prescription lens was introduced in 1947 by the Armorlite Lens Company in California. These lenses were made from Columbia Resin 39 which is why they are also referred to as CR-39 lenses. They remain a popular choice today due to their high-quality optics and lightweight feel. They are also a cheap option of spectacle lenses.
Polycarbonate lenses were first introduced in the 1970s by Gentex Corporation. They were meant for safety glasses but became increasingly popular in the 1980s and remain a popular choice today.
The polycarbonate material was originally used for helmet visors for the US Air Force as they offered a strong bulletproof quality. Due to the high-impact resistant nature, it remains a popular choice for children’s prescription glasses, safety glasses and sports.
Polycarbonate lenses are lighter than CR-39 lenses. However, an even lighter weight prescription lens was introduced in 2001 and is called Trivex. This lens is also a high impact choice and has a higher Abbe value giving it a further advantage.
High-index plastic lenses
High-index plastic lenses were introduced by popular demand for even thinner and lighter eyeglasses options. Their higher index of refraction makes them thinner and lighter than CR-39 prescription lenses.
Index of refraction
The index of refraction in a prescription lens for glasses measures the efficiency of the material to refract light. This depends on how fast the light travels through the material.
Light moves slowly through lenses with a higher refractive index. This means that the light ray will refract more. Thinner lenses tend to have higher refractive indexes than lenses made from a thicker material.
The refractive index of prescription lenses ranges from 1.498 in CR-39 plastic to 1.74 in a range of high indices lenses. Therefore, lenses made from CR-Plastic will be the thickest lens regardless of their prescription power or design. The thinnest lens will be a 1.74 high-index plastic lens.
The Abbe value measures the material of the lenses dispersion of different wavelengths of light. It is also known as the V-number.
A high V-number indicates a low dispersion. A low abbe value can result in chromatic aberration. This is an optical error which causes coloured halos around objects and light. Abbe values of prescription lenses range from 59-30.
The Abbe value is named after the German physicist Ernest Abbe, who defined this optical measurement.
Aspheric lenses reduce the amount a lens might bulge out of the frame. An aspheric design will give your lenses a slimmer profile, making them more attractive.
An aspheric lens will feature a change in curvature from the centre of the lens to its edge. Due to the flat nature of aspheric lenses, they do not magnify your eyes as much as spherical lens designs. They can also enhance the clarity of the wearer’s peripheral vision.
Aspheric designs are featured in most high index plastic lenses for the best appearance and optical performance. An aspheric design will increase the cost of the lenses with Polycarbonate or CR-39 lenses.
Minimum Centre Thickness
Due to the BS/EN standards for impact resistance, a laboratory can only make the lenses so thin.
Lenses to correct myopia are concave lenses which are thinnest in the middle at the optical centre with a bigger edge thickness. Convex lenses feature a lens which is thinner at the edges. These are used to correct long-sightedness.
Polycarbonate and Trivex lenses for myopia are high impact resistance and can afford to have a centre thickness of just 1.0mm. Other lenses for myopia must be thicker at the centre to pass the BS/EN standards for impact resistance.
The thickness of your lenses will depend on the size and shape of your optical frames. A small and well-centred frame will allow you to have a thinner and lighter lens.
Aspheric lenses made of a high index material and worn in a small frame are the thinnest option of lenses available.
The lenses you choose will also influence your choice of frames. For example, if you have a high prescription which requires thick lenses concave lenses, you may decide against rimless frames for aesthetic reasons.
There are many lens treatments available which can optimise the comfort, durability and appearance of your lenses. The following are highly recommended:
Lightweight glasses lenses are more prone to scratching and abrasions than glass lenses and require a scratch-resistant coating.
Although there is no way to make your lenses completely scratch-proof, an anti-scratch coating, also known as a hard coat, can make the lenses of your glasses almost as scratch resistant as glass. This coating will make it harder for your glasses to become scratched when they are dropped or rubbed against a hard surface. However, it’s always worth considering lenses which offer a warranty against scratches.
Anti-reflective coating (AR coating) improves contrast and clarity of spectacle lenses by getting rid of reflections. This makes them perfect for night and will also make your lenses less visible.
An anti-reflective coating is necessary for high index lenses as these lenses reflect more light thus increasing glare. Everyone could benefit from having an anti-reflective coating on their glasses. This is especially true of people with high prescriptions and those who find their vision decreases at night.
Exposure to ultra-violet radiation from the sun has been linked to many eye-related problems including cataracts and macular degeneration. It is therefore important to protect your eyes from the sun with a UV-blocking treatment on your lenses.
Almost all high-index plastic lenses include 100% UV protection. However, CR-39 plastic lenses will need an additional coating applied to ensure that they offer UV protection.
Photochromatic treatment allows lenses to automatically darken in response to the suns UV rays and return to clear when indoors. Photochromatic treatment is available in all lenses no matter what their material or design.
Photochromatic lenses, i.e. Transitions, also help protect against high-energy visible (HEV) blue light emitted by the sun and electronic devices and screens (computer, smartphones) to reduce eye strain and eye fatigue.
Blue light blocking lenses
Blue light blocking lenses help to minimise the impact of High Energy Visible (HEV) blue light. Lenses that blue light will reduce the discomfort felt from harsh screen lights. These are particularly helpful for the evening as too much exposure to blue light before bed inhibits your melatonin, which tricks your brain into thinking it’s still daytime and you should be awake.
High index lenses will suit any prescription and are highly recommended for those who have a strong glasses prescription.
When choosing high index lenses, you should take the advice given to you by your optician. There are a variety of high index materials to choose from. The higher the index, the higher the cost of the lenses.
No matter what you decide, we recommend choosing a high index lens with an anti-reflective lens coating. This will ensure optimal clarity of vision as an AR coating will eliminate reflections.
Tips for choosing the right pair of glasses for you
Below are some tips on how to choose the best pair of glasses for your specific eye condition.
If you’re quite short-sighted, consider these points to minimise the thickness of your lenses, even if you’re choosing thinner lenses.
- Plastic full-rimmed frame which will hide any edge thickness better than a metal-rimmed one.
- Try not to order a frame with an eye size of more than 50mm.
If you’re quite long-sighted, consider these points in addition to choosing thinner lenses:
- Plastic full-rimmed frame which will hide any centre thickness better than a metal-rimmed one.
- Try not to order a frame with an eye size of more than 50mm.
- Try to stay away from semi-rimless or rimless frames as the edge thickness of your lenses (the thinnest part) will need to be made thicker for them to be glazed into the frame successfully. This will have a knock-on effect on the centre thickness, making the lenses look distorted.
- Order an anti-reflection coating to reduce troublesome reflections from the lens surface.
- If you’re not sure, please ask one of our helpful qualified dispensing opticians