Glass lenses are often more hardy and resilient against scratching and therefor often the choice of lens for people working in dusty environments or areas where spectacle maintenance is difficult. Glass lenses are generally less impact resistant and often needs to be hardened to make them safer, as breakage of a spectacle lens close to the eye can cause extensive and often irreparable damage.
Plastic spectacle lenses on the other hand are very lightweight, less than half the weight of glass lenses, and are at least four times more impact resistant than glass lenses. They are not as scratch resistant as glass lenses and therefor need to be treated with a special coating to improve their scratch resistance. These coatings make them quite tough and their life expectancy is generally doubled provided that proper care is taken.
How to care for your Spectacle lenses
Spectacles are optical devices not very dissimilar to a camera and therefor deserve to be treated similar in its upkeep and care.
The most damage to spectacle lenses occur when they are cleaned with the incorrect materials. It has become the norm to use the cleaning cloth supplied with your spectacles to wipe lenses down. It was found that these cloths through time collect sand and hard dust particles that can cause immense damage to your expensive spectacle lenses. If you wish to use these cloths, best you ensure that they are regularly washed and kept in a separate sleeve where it would be protected against dust and hard particles.
Tissue paper and paper towels are also not advisable as they are made of hard wood fibres that can cause damage to sensitive non-reflective coatings. Continuous use of paper towels or tissues will result fine scratches developing on your spectacle lenses. The very best material/fabric to use for cleaning lenses, we have found to be cloths made of cotton. Normal dishcloths, towels and lint-free dusters are quite acceptable. If you have spectacle lenses with a non-reflective coating it is advised that you acquire a micro-fibre cloth specifically designed for cleaning these highly specialised and sensitive lenses.
Lens sprays are available to lift greasy dirt from lenses and are very effective. Care should however be taken that no hard particles are present on the lens that could cause scratches or damage to the sensitive non-reflective coating.
General cleaning procedure
If your lenses are dirty with visible particles, it is advisable to rinse the lenses under running warm water in order to remove all the loose particles. Generally greasy deposits will remain on the lenses and these may have to be soaped off with a non-greasy soap such as a dish liquid. Remember that facial and body soaps contain moisturisers which will be hard to rinse off after the lenses have been soaped down. Once the lenses have been soaped down properly it should be rinsed again with warm running water to remove all the soap. The lenses should then be wiped down with a cotton cloth of the type described above. Non-reflective lenses may require a further clean with a micro-fibre cleaning cloth.
Cleaning rimless or semi-rimless glasses can be quite treacherous as breakages often occur when the wrong technique is used. The spectacle should be cleaned by holding the lens that is cleaned. Cleaning the one lens while holding it by the other will cause stress on the frame which may result in a breakage.
Essentially you should look after your spectacles the way you would care for an expensive camera…. WITH CARE!