Refractive index (index) glass lenses – most important indicator of class spectacle lenses. General rule: The higher the index, the smaller the thickness and curvature of the lens, giving the same diopters. And the stronger the lens you need, the more noticeable difference. In practice this means that the lenses with a high index will be easier, they will be less distorting your face and eyes, they will be easier to pick up a slim and stylish frame. In modern lenses index ranges – for optical glass within 1,5 – 1,9 and for optical plastic – in the range 1,5 – 1,7. Lens with index close to 1.5 are considered low-index and with index greater than 1.6 – high viscosity. Material spectacle lenses – now the choice lies between the glass and plastic.
Definitely an advantage can not give neither the one nor the other lenses. The advantages of plastic lenses – it's easy – the weight of an optical plastic half glass and because of your glasses with plastic lenses are much lighter. Less traumatic than glass, because plastic is resistant to splitting and its fragments are less dangerous. Plastic provides a great opportunity for treatment, in particular for coloring lenses. The advantages of glass lenses – in general the index of refraction (index) glass lenses is higher than plastic.
In addition, the strength of the glass is higher than that of plastic. This means that the quality of glass lenses, with equal diopters, may be thinner and flatter than plastic. Thus, the choice of points is to begin with the choice of lenses, especially if you need correction expressed violations with many diopters. choosing frames for glasses Eyeglasses Frames should adequately "straighten" your eyeglass lenses. What you should know when choosing a frame for spectacles: the choice of frames needed to pay particular attention to such details as the mobility nosouporov – hard nosoupory often put pressure on the nose and cause rapid fatigue. It is advisable to choose a frame with a soft silicone, mobile nosouporami. Size earhook has to match the distance from the rim to the convexity for the auricle. Temples should not exert pressure on the temples and the area behind the ear. The frame should be convenient and not cause fatigue even after long use. Cheap metal frames, of unknown origin in contact with skin can cause severe allergic reactions and irritation. If we talk about glasses, not only as an instrument for vision correction, but also as a means of image and style of a man, the role of properly chosen Classes here is undeniable.