Lens types, coatings & materials
At Eyediology we will guide you through the different optical lenses and help you make the right choice.
Choosing the right spectacle lenses is critical for two reasons:-
- To ensure your visual requirements are met
- To ensure that your glasses feel and look great.
We will explain the features and benefits of the more popular types of lenses below:-
- Thin and light lenses – Also called High Index lenses
- Anti Reflection Lenses – Also called Multi Anti Reflection Lenses
- Bifocal Lenses – See clearly at a distance and when reading
- Varifocal Lenses – See things clearly at all distances
When choosing your lenses there are a few considerations of what might be best for your prescription. This will be determined by what your individual needs are, as well as the prescription that you need.
A single vision lens, is when the prescription is the same throughout the entire lens. Single vision lenses are used for nearsightedness, farsightedness and astigmatisms. The prescription is the same at the top and bottom of the lens.
A bifocal prescription is when lens strength needs to be increased at the bottom of the lens, versus the top of the lens. Bifocal lenses usually have a line that runs through the lower portion of the lens which separates the distance and reading prescriptions.
Varifocal or progressive lenses, are bifocals that have no visible segment separating the distance and reading prescription. The lens is seamless throughout the entire lens.
Sometimes called computer lenses or specialist reading lenses, these are specifically designed for people that required clear vision a short and intermediate ranges i.e. from reading distance to seeing objects just over arms length away. This makes them ideal as specialist work lenses, particularly for people that work in an offices with alot of work being carried out on computers.
Photochromic lenses will become darker when exposed to UV light. For example, walking outside with these types of lenses, means that they become darker, similar to sunglasses. When you return indoors again and the UV light is removed, the lenses transition back to clear lenses again.
Polarized lenses have a filter that is part of the lens that reduces and eliminates how much reflective light enters the eye while wearing the glasses. Glare can take place on asphalt, snow, water or on a windshields. The polarized lenses reduce this glare, creating clearer, cleaner vision.
Prescription sunglasses are exactly the same as regular glasses, except that they have the same tint on the lenses as sunglasses would. Prescription sunglasses can be made in the same prescription strength as regular glasses.
The polished surface of a glasses lens can reflect light in a similar way to a clear piece of glasse (e.g. a window pane) can. Under certain conditions this can lead to unwanted reflections and ‘ghost’ images being seen; reducing the visual quality for the wearer and being aesthetically displeasing for people seeing you. With the application of coating this effect can be drastically reduced, making you glasses look much more appealing on you. Other coating will protect the surface of your lens from minor scratching and can make them easier to clean and maintain.
An anti-reflective coating allows more light through the lenses, while reducing reflections and glare. Your eyes can be seen more clearly through the lenses as well. An anti-reflective coating is very useful when driving and working on computers for extended periods of time.
Scratch resistant lenses have a clear coating over them, that reduces and even eliminates scratches and marks on your lenses. The lenses last longer and there are fewer problems with vision and clarity while wearing the lenses.
CR39 1.5 Index Plastic
This is a plastic used to make lenses. This plastic is used because it is light and easily made and cut making production of lenses faster. However, this plastic can not always be used for high index lenses and can become scratched more easily.
High Index Lenses
A high index lens is a newer version of the above plastic lens. It is even thinner and lighter than conventional plastic or glass lenses, as well as flatter too.
Aspheric and bi-aspheric lenses
Standard single vision lenses are described as having a spherical surface, i.e. there angle across the surface of the lens is uniform like the surface of a sphere. In aspheric lenses, the angles of curvature is not equal across the surface of the lens; this allows for better visual quality across the lens, not just at the optical centre. Aspheric lens also have a flatter lens profile meaning that thinner lenses can be produced in comparison to standard spherical lenses. These benefits are further enhanced in bi-aspheric lenses that have a flatter frontand back surface. This is only achievable using complex computer aided design to produce the lens.
Glass lenses were at one time the standard lens that was placed in all frames. Glass is more scratch resistant, but much heavier than the plastic that is now used. This is extremely important when a prescription strength is very strong. A glass lens will be very thick and heavy, versus using a plastic lens. However, glass is still is used for lighter prescriptions, due to their scratch resistance and clarity.