First off: only 10% of spectacle lenses are made of classic, mineral glass (silica), the remaining 90% are made of plastic (predominantly CR39 and polycarbonate). These have the advantage of being lighter, but also more durable and resistant to impact, light and UV-rays.
To make your choice easier, we have brought together the most important lens types, thicknesses and finishes.
Which spectacle lenses are right for me?
The basic distinction is between single vision and multifocal lenses:
Single vision lenses:
As the name suggests, single vision lenses correct just one type of sight deficiency – either short-sightedness (myopia), far-sightedness (hyperopia), or age-related sight deficiency (presbyopia) with the help of reading glasses. These lenses are used in single vision glasses.
Nowadays the most common types of multifocal lenses are varifocals or lenses to aid close-range vision. Bifocal and trifocal lenses are considered outdated, which is why we don’t use them.
- Varifocal lenses:
Varifocal glasses are usually worn after the age of about 40. Opticians recommend them if you have to either switch between different glasses for different distances (close-range and/or far away) or frequently put on and take off your glasses.
In addition to correcting long- and/or short-sightedness, varifocal lenses also correct presbyopia and enable sharper vision, whether regarding things up close, far away or at distances in between. There is a smooth and unobtrusive transition from upper to lower when switching focus from distant to near objects. This is why nowadays varifocals are used instead of bifocal or trifocal lenses.
- Close-range lenses:
Close-range lenses are used particularly for computer glasses and workplace glasses. Similar to varifocal lenses, close-range lenses allow for a smooth transition between different visual fields. However, in this case there is a greater focus on the immediate surroundings and mid-distance, which comes at the cost of longer distances. These glasses are perfectly suited to the workplace, to desk work or as hobby glasses, because they optimise vision in relation to screens and the surrounding environment.
Important point: due to the focus on close-range vision, these glasses should not be worn while driving.
Which refractive index is right for my prescription?
The higher the dioptre number, the thicker the lens – for glasses wearers with high corrective values this means that heavier lenses are used in the glasses. In the long-term this can be unpleasant for the wearer.
This is where the refractive index, which can positively influence and/or clearly reduce lens thickness, comes into play. Lenses with a high refractive index are thinner for the same corrective values than a standard lens with a refractive index of 1.5.
The refractive index
The refractive index represents how efficiently a lens can refract light. A higher index means a greater refraction of light, which is why a lens with a higher refractive index can be manufactured in a thinner form. The refractive index also depends on the lens material. With plastic it varies between 1.5 and 1.74, while mineral lenses can reach between 1.5 and 1.9. Due to its higher density, mineral glass is fundamentally thinner than plastic – but also heavier and more liable to break.
Here is an overview of refractive indices:
Lens thickness of minus lenses
Lens thickness of plus lenses
Refractive index 1.5
These spherical standard lenses are used to correct minor sight deficiencies up to a value of ±2.00 dioptres. They are unsuitable for higher values.
Refractive index 1.6
Lenses with a refractive index of 1.6 are used for dioptres ranging from ±2 to ±4. They are significantly thinner and about 20% lighter than standard lenses.
Refractive index 1.67
Extra thin lenses with a refractive index of 1.67. So thin that even high dioptres of between ±4 and ±6 don’t draw attention to themselves – or weigh you down, as they are about 40% lighter than the 1.5 standard lenses.
Refractive index 1.74
NEW - Super thin lenses with a refractive index of 1.74, which are up to 60% thinner and lighter than the standard version and can correct dioptres from upwards of ±6.00.
Aspheric lenses help to improve image quality and prevent distortion at the edges of vision. With plus lenses they also have the effect that the eye size doesn’t appear greatly increased, while with minus lenses they have the opposite effect, namely that the eyes don’t appear reduced in size. Thus the eyes appear more natural. At Mister Spex lenses with a refractive index of 1.67 are aspheric as standard.