The sun of these days beats down and is felt not only on the skin, but also on the eyes that are looking for a bit of shade to shelter from the damage that solar radiation can also cause to sight. In the city, but especially when you go on vacation and spend a lot more time outdoors, the only way to protect your eyes from these harmful effects is to use sun lenses, among these photochromics have the characteristic of modulating the percentage of darkening depending on the light intensity.
What are photochromic lenses
All of us will have heard of photochromic lenses and have broadly understood what they are, but perhaps it is not clear what they are for and why it is important that the lenses we choose for our sunglasses have this characteristic. . “Photochromic is a lens made with a particular material that has the ability to change, in a reversible way, its chromatic state depending on the radiation to which it is exposed”, explains Luigi Mele, ophthalmologist surgeon at the Luigi Vanvitelli University – Naples and President of the Scientific Committee of the Salmoiraghi & Viganò Foundation. “More simply, the photochromic lens progressively darkens under the action of UV rays and lightens indoors”.
What are they for
The main damage produced by sun exposure to our eyes derives from the absorption of UV radiation and visible light. “The photochromic lenses have a total absorption for UV and a high absorption of visible radiation, mainly based on the color”, explains Andrea Piantanida, eye surgeon at the Lariano Ophthalmology Center, Cernobbio-Como and member of the Scientific Committee of the Salmoiraghi Foundation & Viganò. “For this reason, a photochromic lens can fully be counted, in the field of protective lenses, among absorbent lenses, or rather as a lens capable of acting as a selective filter for the harmful components of solar electromagnetic radiation”.
When and to whom it is needed
In some cases, photochromic lenses may be a necessity linked to the presence of certain eye diseases that require special protection. This is the case of subjects suffering from macular degeneration, keratitis, cataracts or strabismus. But the photochromic lens is also recommended in relation to some climatic-environmental conditions, for example in cases of strong exposure to solar radiation. “Today, for reasons related to the activity exercised, situations in which the eye is subjected to prolonged exposure to radiation with violent contrasts of intensity both when the activity is exercised outdoors, but also when the he activity is carried out indoors as happens when you work with the artificial light of lamps or the video terminals of the offices ”, continues Mele. Geography also plays a role. Exposure to UV radiation is a function of multiple factors such as latitude (at the equator the exposure is greater), climate and atmospheric conditions, altitude, the amount of radiation reflected by the various types of earth’s surface.
A practical solution
Since the photochromic lens can be used both indoors and outdoors, it is a valid alternative to sunglasses. “Some people – explains Piantanida – find it difficult to use different glasses when the light intensity varies; the prescription of the photochromic lens can be the solution to this problem due to the habits of people and in particular of children who are always running and do not have the patience to change glasses “.
Third generation photochromic materials
Thanks to the creation of third generation materials, it is now possible to produce progressive photochromic lenses. “These lenses – says Mele – currently represent the most technologically advanced result in terms of ophthalmic lenses: in fact, in this case, in addition to the results obtained from research during the activation of the photochromic process, those achieved in the design phase are combined. of the geometry of a progressive lens, thus achieving a lens in which you have comfortable vision and good protection against glare thanks to the high absorption value that this lens possesses together with an almost total protection from UV radiation “.
How they are made
Photochromic lenses are made up of photochromic pigments that have the characteristic of modifying their color depending on the electromagnetic radiation through a reversible chemical process in the presence of heat. “They can be built in both glass and organic material, but those in third generation organic material have superior darkening or lightening characteristics and can be made in different colors,” explains Piantanida.
The differences compared to sunglasses
But what is the difference between a ‘simple’ sunglasses and photochromic lenses? Mainly the difference lies in the ability to modulate the transmittance (editor’s note: the ability of a material to let a part of the incident light pass through) of the electromagnetic radiation. “In traditional sun lenses – explains Mele – the transmittance is fixed, while in photochromic ones it is modulated according to the lightening or darkening”. Therefore, photochromic lenses can be used in any natural or artificial light conditions. “Due to their chemical and constructive characteristics – continues the expert – these lenses guarantee ocular protection both from solar radiation and from artificial ones, characteristics of work environments, and represent an ideal solution for everyone and at any age”.
Not just for adults
The choice of photochromic lenses is not just for adults. “Reducing the phenomena of glare and strong lighting – explains Piantanida – exerts a control on the imbalance of ocular motility avoiding the onset of ocular deviation or strabismus which would lead to double vision. It is therefore important that even from an early age parents use photochromic sun lenses for their children with refractive defects, considering them a real therapeutic weapon “.