What are Photochromic Transition Lenses? Available brands and Price in Nepal

Ophthalmic LensesOphthalmology and Optometry Notes

By Eye Health Nepal Last updated Jun 3, 2021

Introduction of Photochromic/ Changeable/ Transition Lenses

The word “photochromic” derives from the two Greek words “photos” and “chroma” which mean

Photo = Light

Chroma = Colour

So it simply means something that changes colour in response to the light. Photochromic lenses change its darken and lighten shades depends upon the exposure to UV light.

Since 1960s photochromic lenses are available, traditionally these type of lenses were made from Glasses but in this modern time Photochromic lenses which is also known as changeable lenses, Day and Night lenses or transition lenses are now available on plastic and polycarbonate material and now also they contain organic (carbon-based) molecules that react to light in a slightly different way. Now many of premium ophthalmic lens manufacturer produce customized photochromic lenses also which mean they can offer different categories of sun protection to meet specific needs of customers.

How do photochromic lenses work?

The glass version of these lenses achieve their photochromic properties through the embedding of microcrystalline silver halides (usually silver chloride) in a glass substrate. Plastic photochromic lenses use organic photochromic molecules (for example oxazines and naphthopyrans) to achieve the reversible darkening effect. These lenses darken when exposed to ultraviolet light of the intensity present in sunlight, but not in artificial light. In the presence of UV-A light (wavelengths of 320–400 nm), electrons from the glass combine with the colorless silver cations to form elemental silver. Because elemental silver is visible, the lenses appear darker.

Back in the shade, this reaction is reversed. The silver returns to its original ionic state, and the lenses become clear. (1)

Reaction Time (Darkening & Lightening timings)

Typically, photochromic lenses darken substantially in response to UV light in less than one minute, and continue to darken a little more over the next fifteen minutes.(1) The lenses begin to clear in the absence of UV light, and will be noticeably lighter within two minutes, mostly clear within five minutes, and fully back to their non-exposed state in about fifteen minutes. It may also depends upon other variables such as temperature, thickness, exposure.

Advantage

It help your eyes to cope up as they react to different light conditions during the day
Good Photochromic lenses blocks 100% of most harmful radiation
Protects you from UV which can cause lost of harm to eyes. (UV Rays)
Gives a visual comfort whether indoor or out door

Photochromic lenses disadvantages

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These lenses do not adjust immediately.
It could take up to two minutes for the lenses to adequately change from light to dark or vice versa
Another disadvantage for some users is that they will not darken when worn inside vehicles because wind screen green glass absorbs virtually 100% of UV light, so without UV light these lenses won’t darken.
It gradually loses its darkening ability with time.

What are transition lenses?

In United States photochromic lenses are made by Transitions Optical and many people including some eye care practitioners mistakenly call all photochromic lenses as based on their product name “transitions lenses” or “transition lenses.” But there are many brands of photochromic lenses offered by different lens manufacturers in market.

Available Photochromic lenses from various brands in Nepal

Photo chromic are available in single vision, bifocal and progressive lenses forms in Nepal. There are many best photochromic lenses available nowadays.

Popular brands of photochromic lenses sold in the Nepal are as follows.

Crizal UV Transition Classic Thin & Light
Eyezen+ Crizal Transitions Signature
ZEISS PhotoFusion
ESPACE Plus transition
Varilux Progress transition
SOLIO Photochromic lens
Hoya Sensity Photochromic Lenses

Price of Photochromic Transition Lenses in Nepal

Price of these lenses are depends upon power of lenses, model, brands, coating and refractive index of the lenses. So for exact price for your price please visit your nearest optical shops.

Reference:

1. Photochromic lens. (2020). Retrieved 4 September 2020, from https://en.wikipedia.org/wiki/Photochromic_lens

2. https://eyehealthnepal.com/wp-content/uploads/2021/05/photochromic-lens-vector-uv-can-260nw-595609718.jpg