Do you need High Index lenses?

When it comes to prescription glasses, a lot of consumers are still in the dark. There is a lot of terminology that is used in the Optometry practice to describe products and procedures, which often aren’t explained as thoroughly as they should be. A lot of this is around prescription lenses, and the options each customer has. In this post, I’m going to give you a little info on High Index lenses.

Firstly, what exactly are high index lenses? In extremely basic terms, they are prescription lenses made from a more compact material than the ‘standard’. Now, I could get extremely technical on this topic, but given a lot of my readers are from outside the industry, I’ll stick to the basics this time around! Lens materials are generally listed in the refractive index, 1.5 being the ‘standard’ across the industry. The higher the number equals a higher refractive index, and thinner and more compact the lens material. The most commonly used lens indices across Australia at the moment are: 1.5, 1.53, 1.6, 1.67 ad 1.74. There are more, but they have quite limited ranges of lens designs to choose from, and I don’t want to turn this into a novel;)

img_8915

The first reason your Optometrist or Optical Dispenser may recommend you consider high index lenses, is due to your prescription. When you have a prescription that requires a plus lens (+) the thickest part of the lens will be the centre. And when you require a minus lens (-), the outside edge will be the thickest part. The stronger (higher) the prescription, the thicker the lens will be. Let’s take a look at a few benefits of high index lenses for both plus and minus lens types.

img_1339Plus lenses

Plus lenses are thickest in the centre, which means you re more likely to see more edget thickness in a smaller frame. However, having the thickness in the centre means that once your prescription is close to or more than +2.00, the weight of your lenses can become an issue. On top of this, thickness in the centre of your lenses means there is more room within the lens for light to refract, which can cause aberrations resulting in vision that isn’t as ‘crisp’ as it could be for you. By looking at high index lens options you:

  • May reduce the weight of your lenses resulting in a more comfortable pair of glasses
  • Have less aberrations within the lens meaning a clearer result for your visual correction
  • Cosmetically your lenses will not look as ‘magnified’ to people looking at you, due to the more compact finish.
  • High index lenses are stronger than the standard material, so you will get better longevity from them too.

Minus lensesimg_1338

Minus lenses are thickest at the outside edge, and with high prescriptions, the lens can be sometimes seen to ‘overhang’ the frame. This is most noticeable with metal frames, but depending on the strength of your prescription, may also be noticed with acetate frames. As with high plus lenses, weight can be an issue, and having too much thickness on the outside of your prescription can cause a ‘swimming’ effect in your vision in the peripheral zones, especially when wearing progressive lens designs. Looking at high index lens options for you could:

  • Reduce the weight of your glasses resulting in more comfortable eyewear
  • Compact and reduce the amount of aberrations and ‘swim’ effect in your peripheral vision
  • Fit into your chosen frame better meaning you are less likely to have issues down the track
  • Cosmetically more appealing as the thickness won’t be as visible around the edge of your frame.
  • High index lenses are stronger than the standard material, so you will get better longevity from them too.

 

Below are some examples of when consumers should consider high index lenses, with any type or strength of prescription:

  • When you are looking to purchase eyewear with a higher than usual base curve, most commonly wrap sunglasses. The benefits in this case would be the more impact resistant properties of the lens material, as well as minimising any distortions to the side of the lens. When considering wrap sunglasses there are a lot of things to consider including lens design depending on your prescription, so always ensure you ask if your prescription is a good match for the frame you like.
  • When purchasing a semi-rimless frame. These are the frames that look to have frame at the top, but not the bottom. These designs actually have a piece of nylon attached to both sides of the lens area, which holds the lens in place. When your lenses are being made, a groove is bevelled into the centre of your lens where the nylon will sit in place. High index lenses are beneficial in this example again, for the strength – to help avoid chipping on those raw outside edges. Your Optical Dispenser should request a minimum edge thickness when you order this type too, also helping reduce the likelihood of lens chipping.
  • When purchasing a rimless frame design. Rimless frames are also referred to as 3 piece designs; two temples (arms) and the bridge (across the nose). These frames require the lenses to have holes drilled through them for the frame to then be fitted into place. You must have a high index lens material in this case as a 1.5 index will crack. On top of this, in a rimless design if your lenses are too heavy, the entire frame will always slip forward nomatter how well it is adjusted to your face. Balance and weight distribution is extremely important when considering a rimless frame design.
  • All children’s glasses! You guessed it: Mainly for the impact resistance, however there are obvious benefits for minimized weight (better fit) and thinner lenses (better clarity) as well.

So in summary, there is a reason every single consumer should at least consider high index lenses, but every single pair of glasses needs to be considered independently. Most reading glasses that stay at home with a prescription under +2.00 for example, wouldn’t need to be high index lenses unless the wearer is extremely sensitive to weight.

As always, have a more detailed discussion with your Optometrist or Optical dispenser on your specific needs, wants and expectations of your lenses. They will be able to inform you when it would be beneficial to go down this track, and give you examples of what to expect with the different outcomes for each material.

If you would like more detailed information on any of the above, please email or message me – I’m always happy to help! And as I mentioned earlier, this is a very basic summary of the topic….I could honesty write for days! But I hope this helps empower some of you to investigate a little further than you normally would. After all, when you have to wear them every day, your eyewear is one of the most important purchases you make.

Em x

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The Eyewear Girl is an Eyewear Influencer and blogger from Australia. I share reviews, tips, fashion and advice on all things Eyewear and Optical. Eyewear should enhance you personality, not hide it!

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