The simplest form of spectacle or contact lens is the single-vision lens, made to a single prescription to correct a particular eyesight problem. Concave lenses are used to correct short sight and convex lenses to correct long sight. Concave lenses are generally thinner in the centre than they are at the edge and convex lenses are usually thinner at the edge than at the centre. The curvature of the lens, its thickness and weight will depend on the amount of long or short sight it is designed to correct. The lens material will also influence the thickness and weight of your lenses, as will the size and shape of the spectacle frame you choose. Traditionally, spectacle lenses were made of glass but most lenses are now lightweight plastic and there is a wide range of materials available to suit your prescription and lifestyle.
Stock powers Plastic lenses
Stock powers relate to to the range of lens powers available off the shelf. These have limited ranges both in –(minus) and +(plus) powers (typically sphere powers total +/-6.00 and cylinder powers +/-2.00, so +powers add up to +6.00 sphere in total with a cylinder power of up to -2.00, and -powers would be -6.00 sphere with cylinders of +2.00)a bit confusing I know, however, if you are not sure if your prescription falls outside these ranges please contact us or we will contact you when we receive you prescription to discuss your lens options and extra costs involved in producing these custom lenses.
Polycarbonate lenses are thinner and lighter than traditional plastic eyeglass lenses. They also offer high ultraviolet(UV) protection and are up to 10 times more impact-resistant than regular plastic lenses.
This combination of lightweight comfort, UV protection and impact resistance makes polycarbonate lenses an excellent choice for sports eyewear, safety eyewear and rimless glasses.
Polycarbonate was developed in the 1970s for aerospace applications, and is currently used for the helmet visors of astronauts and for space shuttle windshields. Eyeglass lenses made of polycarbonate were introduced in the early 1980s in response to a demand for lightweight, impact-resistant lenses.
Since then, polycarbonate lenses have become the standard for safety glasses, sports goggles and children’s eyewear. Because they are less likely to fracture than regular plastic lenses, polycarbonate lenses are also a good choice for rimless eyewear designs where the lenses are attached to the frame components with drill mountings.
Lens ranges or for these smaller than ordinary plastic lenses. Plus lenses max at +4.00 shere and a max -2.00 cylinder and Minus lenses max -6.00 sphere and max+2.00 cylinder
Bifocal lenses contain two optical corrections with a distinct dividing line between the two parts. The most common use of bifocals is for people who have become presbyopic and need a different prescription for close work. The upper part of the lens corrects distance vision and the lower half is for near vision. Trifocals are also available that have three sections and incorporate a correction for intermediate vision. Bifocals and trifocals come in a range of designs but nowadays varifocal lenses are much more likely to be prescribed.
Varifocal or progressive lenses
Varifocal lenses, also known as progressive lenses, are used for correcting presbyopia but unlike bifocal lenses have no visible dividing lines between the different corrections. Instead they have a graduated section in which the power of the lens progresses smoothly from one prescription to the other, allowing the wearer to see clearly at all distances. These lenses also have the benefit of looking better – they don’t draw attention to the ageing process. A range of varifocal designs is available depending on your lifestyle and occupation. Modern lens technology means that there are many different designs and materials to choose from. Your optometrists or dispensing optician will be able to advise you on the best lenses to suit your individual requirements.
High-index and aspheric thin lenses
If you need high-powered lenses you can improve the weight or appearance of your glasses with special lens materials and designs. High-index materials and aspheric designs mean that lenses can now be made thinner, lighter and better looking than traditional lens types. High-index materials make lenses for short sight thinner, while aspheric designs that minimise the amount of material make lenses for long sight both thinner and lighter. The stock power ranges for these lenses are quite extensive and to vast to list. Should your prescription fall outside our pricing structure we will contact you with a costing before carrying out any work.
Whatever your prescription, it is important to protect the eyes against excessive ultraviolet (UV) radiation. Protection is needed to avoid reflected light from sand and snow or if you spend long periods out of doors, particularly in the summer. Prescription sunglasses can be made with single-vision, bifocal or varifocal designs to offer the same standard of protection as non-prescription sunglasses.
Safety and sports glasses
Special lenses and frames incorporating eye protection are available for a variety of safety and recreational uses.
Anti-reflection coating (mar)
Spectacle lenses can be provided with anti-reflection coatings which virtually eliminate distracting reflections off the lens surfaces. Reducing reflected light is particularly helpful for computer users and for night driving. Anti-reflection coatings also improve the cosmetic appearance of your glasses and can make thick lenses look thinner.
Scratch-resistant / hard coating (tough coating)
Plastic lenses are lighter than traditional glass lenses but they scratch more easily. Scratched lenses can be irritating for the wearer and look unsightly. Scratch-resistant coatings are available to protect against damage and prolong lens life.
Multi-coated lenses (hmar)
Multi-coated lenses incorporate a combination of coatings – anti-reflection, scratch-resistant, water repellent and UV – to combine to improve the properties of your spectacles.
What are photochromic lenses? (transitions)
Photochromic lenses are lenses that change their colour according to light conditions. When exposed to sunlight they darken quickly to eliminate glare and to protect the eyes against UV. These lenses are generally nearly clear when it is dark.
Why wear photochromic lenses?
Many people wear these lenses and find them convenient, as they automatically darken in the sunshine and can avoid the need for you to carry prescription sunglasses. Modern photochromic materials react and fade quickly, suit most prescriptions and are more likely to be lightweight plastic than glass.
Driving in photochromic lenses
Concern has been raised about whether it is safe to use photochromic lenses for activities in low light conditions where vision is critical – such as driving at night.
Several factors should be considered:
1. any tint will reduce the amount of light that is entering your eye. The darker the tint the more the light will be reduced. You should not wear a dark tint for night driving.
2. We generally see better in the light than in the dark so the more light that enters your eye the better (providing it is not dazzling you).
3. As some light is lost from reflection from the lens surfaces, the performance of all lenses is enhanced if they are coated with an anti-reflection coating to reduce the reflections from the front and back surfaces of the lens. This is particularly important for the thinner, high index lenses. Your optometrist or dispensing optician will be able to advise you on this.
4. The amount of light transmitted by modern photochromic lenses in their clear state with a multi anti reflection coating, is not much less than that transmitted by a clear, non photochromic lens without an anti reflection coating.
5. Some of the older photochromic materials do not go as clear as the newer photochromic materials. We recommend that you choose the best lens that you can afford, particularly if you wish to use the lenses for critical vision at night.
6. The performance of some of the older photochromic materials degrades over time if you notice that your photochromic lenses do not go as clear as they used to you should buy a new pair.
7. Older people need more light entering their eyes than younger people do. This is because the eye naturally absorbs more light as it ages, meaning that you need more light going into it for the same amount of light to reach the retina.
8. When driving you may find your photochromic lenses do not become as dark as they do outside. Car windscreens (and windows) filter and absorb most of the short wavelength light (near UV) that would normally trigger the darkening process.
For further advice, contact your optometrist or dispensing optician who will be able to advise you on which particular lens is most suitable for you.