Materials
Lenses are made in two materials - plastic or glass. The majority of lenses sold today are of the plastic variety as they are far lighter than glass, and a lot safer. However, sometimes when extremely thin lenses are required for very high prescriptions, glass is the best option.
The thickness of the lens depends upon the prescription in question and the material used. Most people wrongly assume that when we say a ‘1.6' lens, that this means the lenses are going to be 1.6mm thick, but this isn't correct. This number refers to the ‘Refractive Index' of the lens material, and for any given prescription, the higher the number, the thinner the lens. This is because different materials bend light by varying amounts and the higher Refractive Index the greater the effect it has for a given thickness of lens. This means that the same correction and focal length can be achieved from ‘less' lens (material) making them thinner.
How to choose the best lens...
Standard Plastic CR39 (1.5)
This is the basic material that we use on all standard lenses as it is sufficient for most prescriptions. Although, prescriptions with powers stronger than +3.00 and -3.00 will start to look thick, powers between the two will look absolutely fine.
Polycarbonate (1.59)
Polycarbonate lenses are thinner and lighter than traditional plastic eyeglass lenses. They also offer 100 percent ultraviolet (UV) protection and are up to 10 times more impact-resistant than regular plastic lenses.
Developed in the 1970s for aerospace applications, it is currently used for the helmet visors of astronauts and for space shuttle windshields due to its superior impact resistance. This combination of lightweight comfort and UV protection makes polycarbonate lenses an excellent choice for children's glasses, sports eyewear and safety glasses. Also because they are less likely to fracture than regular plastic lenses, polycarbonate lenses are also a good (and strongly recommended) choice for rimless eyewear designs, where the lenses are attached to the frame components with drilled mountings.
Plastic (1.6)
An ideal option for prescriptions up to +5.00 and down to -5.00. 1.6 lenses are 23% thinner than standard plastic. Prescriptions outside this range will again start to look thick.
Plastic (1.67)
Probably the most popular of the thinner lens options. 15% thinner than the 1.6 and 25% flatter, this lens is ideal for prescriptions up to +7.00 and down to -7.00. Again, prescriptions outside this range will start to look thick.
Plastic (1.74)
The thinnest plastic lens available on the market at the present time. 50% thinner than the 1.5 standard plastic and 30% lighter than the glass equivalent. This is great for mid to high prescriptions.
Glass (1.7)
An ideal ‘budget' thin lens for negative power prescriptions up to -10.00. However, the down side is that they will be heavier than the plastic equivalent.
Glass (1.8) and Glass (1.9)
These are rarely used in day-to-day practice, but are especially good for high powered prescriptions. They are an expensive option though.
Some of the brands we supply at Direct Spex...
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