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Lets talk about Lenses

Glass used to the main material to make lenses. Not anymore, thanks to plastic. Yes, for a simple term we called it plastics but there are many names for these sorts of plastics. Let’s name a few which you might come across, High-Index, Polycarbonate, CR-39, MR-7, NK-55, Trivix, ok just to name a few and not list everything.  You must be wondering why so many different types? It all due to the way they are being manufactured, the process steps and the desired function of the lenses.

High Index lens is a much lighter and thinner lenses. The best part is that it allows high prescriptions in Sphere and Cylinder section, typically from -4 to -8. Typically, the stronger your prescription the thicker the edges of the lens. But you do not want to wear spectacle with thick lenses as it spoils your appearances. Therefore, if you have a high prescription, best is to go with High Index lenses and they are more expensive, unfortunately.

Polycarbonate differs from high index. This is a much more common lens partly due to its price comparing to high index. Polycarbonate lenses are hardy, meaning it is strong and impact resistant. If you are into safety, then this lens could be the one for you. Most sports eyewear’s use Polycarbonate as they are thinner and lighter than conventional plastics. Highly recommended for kids eyewear.

Polycarbonate is a thermoplastic that starts as a solid material in the form of small pellets. In a lens manufacturing process called injection moulding, the pellets are heated until they melt. The liquid polycarbonate is then rapidly injected into lens moulds, compressed under high pressure and cooled to form a finished lens product in a matter of minutes.

Trivex is similar to Polycarbonate in attributes. They are both thin, light weight, impact resistant. The difference would be the way Trivex is being produced. Trivex lenses, however, are composed of a urethane-based monomer and are made from a cast moulding process similar to how regular plastic lenses are made. This gives Trivex lenses the advantage of crisper optics than injection-moulded polycarbonate lenses.

CR-39 lens is very similar to Polycarbonate but with slight variance. Its optics are better than polycarbonate as it is nearly as good as glass. It is also less lightly to break, and it retains some hardiness from polycarbonate lens. Let’s see a simple matrix to help you to decide which type of lens you should buy.

Attributes/Material Glass Polycarbonate CR39
Optics Best quality Poor Close to glass
Hardness Poor Very strong Close to very strong
Weight Heavy Light Light
Price Expensive Cheap Cheap

Ok I’m stopping here for now. Happy reading and come back again for more.

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Restricted Substance List (RSL)

These are materials that should not make it into the production of your sunglasses or eyewears.

  • BPA (Bisphenol) Recent research showed there are some health concerns when humans are exposed to high levels. This is a no no raw material.
  • Nickel made it into the list because it causes dermatitis that results in skin irritation. This is a banned material in EU and US.
  • Lead and Cadium are 2 harmful metals to humans that can effect brain developments and the nervous system.
  • Phthalates is what chemical companies use to breakdown plastic and used as solvent in cosmetic products. Eyewear companies can use this chemical to fabricate the frames.

For consumers, it is difficult to identify these RSL in our eyewear. Unless we have the facilities to perform the checking, we are at some risks. The best is to ensure your eyewear manufacturer has certification such as EN ISO 12312-1, EN ISO12870, FDA to mention a few. Normally, you can find these printed at the temple of your eyewear. Ok, I will leave you here today and post another topic soon. Keep reading and stay safe.

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Why Wear Sunglasses?

Many people wear sunglasses for many reasons. Some for fashion while some for medical purposes. Whatever your reason, it is important to know that sunglasses are meant to protect our eyes from harmful UV rays from the sun. A good pair of sunglasses that has UV400 standard will block out UVa and UVb rays.

Do not be fooled by listening to others that say, darker tint lenses provide best UV protection. This is in fact wrong. A UV protected glasses do not need to be dark tint. It can even be clear like your prescription glass. A darker tint lenses without adequate UV coating is in fact more harmful to your eyes. In a darker environment, your retina will open wider to allow more light in. This light contains harmful UV rays that will heat up your eyeballs.

This brings us to the next question, what is UV?

UV stands for Ultra Violent for short. Ultra Violet light is not part of the visible light that we can see but we can definitely feel its presence. There are 3 main types of UV.

UVC

These are the highest energy UV rays and potentially could be the most harmful to your eyes and skin. Fortunately, the atmosphere’s ozone layer blocks virtually all UVC rays. But this also means depletion of the ozone layer potentially could allow high-energy UVC rays to reach the Earth’s surface and cause serious UV-related health problems. UVC rays have wavelengths that range from 100 to 280 nanometers (nm).

UVB

UVB rays have slightly longer wavelengths (280-315 nm) and lower energy than UVC rays. These rays are filtered partially by the ozone layer, but some still reach the Earth’s surface. In low doses, UVB radiation stimulates the production of melanin (a skin pigment), causing the skin to darken, creating a suntan.

But in higher doses, UVB rays cause sunburn that increases the risk of skin cancer. UVB rays also cause skin discolorations, wrinkles and other signs of premature aging of the skin. Overexposure to the sun’s UVB radiation also is associated with a number of eye problems, including pinguecula, pterygium and photo keratitis (“snow blindness”). Because the cornea appears to absorb 100 percent of UVB rays, this type of UV radiation is unlikely to cause cataracts and macular degeneration, which instead is linked to UVA exposure (see below).

UVA

UVA rays are closer to visible light rays and have lower energy than UVB and UVC rays. But UVA rays can pass through the cornea and reach the lens and retina inside the eye. Overexposure to UVA radiation has been linked to the development of certain types of cataracts, and research suggests UVA rays may play a role in development of macular degeneration.


I leave you with some tips:

  • Do wear sunglasses even you are in shade. These harmful UV rays come from all angles and they bounces off surface to reach you.
  • Sunglasses provide excellent contrasts to ease your vision. Especially those polarized sunglasses that blocks out glares.
  • Do not get cheated with darker tint sunglasses that claimed they block out UV completely. Mostly are not UV protected, I will show a simple experience in my next post on how to detect fraud.

What are Polarised Lenses

First we understand that polarized lenses function is to block out glare. Why do have glare and how polarized lenses are able to block it.

We get glares from everywhere, this is due to the lights coming from the sun and hitting at objects. These reflected light travels in a more structured way and usually we term this as horizontal direction. It is this very light that gave us glare and reduce our visibility.

Polarised lenses are coated to block these horizontal light from getting past the lenses. Resulting in better vision experience and better comfort. Polarised sunglasses are best used when you are driving, by the beach, fishing or even playing golf. There are many examples of out door activities that could use polarized sunglasses. As long as you experience glare, you know you need polarized lenses.

There are certain condition where you might find polarized sunglasses are not that suitable. Whenever you view any LCD screen, you will notice at a certain angle, it blacks out completely. If you are required to look at any LCD screen, best is not to use polarized lenses. Luckily we are moving ahead with technology that LCD are going obsolete and replaced with AMOLED. No issues for polarized lens here.


Next we will talk about RSL.