There are a vast number of different lens materials and types available to us in the optical trade. Most different prescriptions could be supplied in a host of different colours, materials and thicknesses, without the correct guidance this can all become terribly confusing. At Gibson Opticians your lens selection will always be assisted by a qualified Dispensing Optician, Optometrist or experienced Optical Advisor. They will advise you on the different options available to you to best suit your prescription, frame choice and lifestyle.
Some of the optical terms used on the promotional leaflets can be quite technical. We’ve put together some information, which might come in handy when you’re deciding what’s best for you.
A single-vision lens is made to a single prescription to correct a particular eyesight problem, short sightedness (myopia), long sightedness (hyperopia), astigmatism and presbyopia.
Bifocals are used for people who need both near and farsighted vision correction. In bifocals there are two corrective lenses on each side of the glasses. The upper part of the lens is used to correct distant vision and the lower half is used for near vision and there is a distinct line between the two lenses. This helps distance vision and reading.
Glasses can also be split into three sections and these trifocals incorporate a correction for intermediate vision. Trifocals are designed to provide clearer vision for near, distant and intermediate range. They are normally prescribed for people who suffer from advanced presbyopia.
Like bifocals, varifocals are used for correcting presbyopia. But unlike bifocals where there is an unattractive bifocal line across the lens, progressive or varifocal lenses gradually change from distance strength at the top of the glasses to reading strength at the bottom. Thus, vision is corrected at different powers depending on where you look through the lens, but there is not a distinct line.
Traditionally, eye glass lenses were made of glass but more modern materials are lighter in weight and thinner. There is a wide range of materials available suiting individual preferences and requirements. Even if you have a high prescription, you can benefit from modern lighter thinner lens materials, which are more visually appealing.
This is the standard material used for glasses. These lenses are almost twice as light as glass lenses. They also have very good protection from UV light and therefore protect the eyes very well. Plastic lenses do not often shatter. They can also be tinted more easily using a variety of colours. With an added coating, they can also become scratch-resistant. CR-39 plastic lenses have a refractive index of 1.498. Their thickness is similar to that of glass lenses.
High-index materials make lenses for short sight thinner and therefore more appealing. These lenses are also lighter and flatter than plastic CR-39 lenses, so there is no need to wear thick, heavy lenses, which magnify your eyes. A high index material is any lens material that has a refractive index higher than glass, which is 1.523.
These lenses are ideal for longsighted people and those who have had cataract removal and have not replaced the eye’s lens with an intraocular lens implant. These lenses are thin and light. Opticians often recommended them to people with very strong prescriptions. An aspheric lens has varying degrees of curvature over its surface and its optical properties give you a larger, more usable portion of the lens and a clearer view throughout the lens compared with the normal spherical designs.
This material may be used for high prescriptions and is thinner and lighter than the plastic CR-39 lenses. It is very impact resistant and therefore ideal if you have small children or are keen on particular sports or any hobby where eye protection is required. It is also often recommended for occupational safety spectacles. This lens, although impact resistant, is more easily scratched.
This material is an alternative to polycarbonate. It is strong, light and thin with a very high impact resistance. Trivex delivers 100% UV protection from both UVA and UVB. It is also scratch and chemical resistant.
Glass lenses can still be made. They are heavier than other materials and people often experience them sliding down their nose. Shattered glass lenses are quite common as glass lenses are more likely to break than lenses made from other materials. Glass is a very hard material, which makes these lenses scratch resistant. Glass is also thinner than plastic CR-39 and the very thinnest materials available are still made from glass so for those with a high prescription can give excellent cosmetic result. Although glass lenses do have good UV protection, it is not as good compared with plastic lenses.
When choosing a lens material, try to decide what characteristics are most important to you.
Tints & Coating
There is a large range of tints available to both cosmetically enhance and improve the performance of the lenses. Tints can be either fixed or photochromatic, which is activated by the UV in the suns rays causing the tint to darken in bright sunlight. A UV inhibitor can also be added to both glass and plastic lenses to give additional protection to the eyes from ultra violet radiation which is a known cause of cataract and macular degeneration.
Another option are polarised lenses where coating is sandwiched between two layers of material in the lenses. A polarized lens only lets light in at certain angles and it cuts down reflections off shiny surfaces. With the removal of the sun’s glare, objects become more distinct and are seen in their true colour. These lenses are favoured by those who partake in water sports, fishing, cycling and a lot of driving as they cut down glare off windows and off wet roads.
Most lenses now can be supplied with an anti-reflection coating which reduces the surface reflection on the lens, this improves the lens performance by reducing glare from oncoming traffic whilst driving and using VDU screens. The cosmetic appearance of the spectacles is more natural so reduces unsightly reflections in photographs and optimizes the appearance of the frame. Multi-coated lenses can incorporate a combination of coatings including anti-reflection, scratch-resistant, water and grease repellent (these can be easier to clean) and UV protection.