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

Lens types

Ok, so this is going to be obvious for some of you, but I know there are plenty of people out there that need to know this – I get asked every day!

Know what you’re buying class #1 is in session, it’s time to get the basics right.

What type of lenses am I wearing?

Single Vision: Exactly as it states, these lenses have one prescription across the entire lens. There are no distortions, visible sections or marks on the lens. img_2830Singe Vision lenses are most commonly made up as reading glasses (near), Distance, or intermediate (computer distance), however your Optometrist can make them up for you at basically any specific distance you need – just make sure you mention it to them at the time of your eye exam.

 

 

Bifocal: Bifocal lenses have 2 distinct sections in them, traditionally Distance and Near. Bifocals can also be used as Near and Intermediate, or Distance and Intermediate. With Bifocals there is a visible section at the bottom called the ‘Seg’ (Segment). This section is clear, but visible due to a different thicknesBifocals of lens on the bottom half, closer to the nasal side of the lens. The most common design of Bifocal is a ‘D-Seg’, because the Seg looks like a letter ‘D’ on its side. This Seg is available in different sizes, and you can also (with some prescriptions) get an ‘Executive Bifocal’ where the segment goes right the way across the lens.  These lenses are now not being used as often as in the past, as all of the technology advancements have moved forward in multifocals lens designs instead. Basically, Bifocals are old technology, and while still useful, we rarely see new glasses wearers opting for them.

 

Green Face a faceVocational lenses: Vocational lenses are the step between a single vision and a full multifocal (See below). They look like a single vision lens with no visible sections, but act more like a bifocal in that they offer 2 different sections. Unlike a bifocal, vocational lenses have a soft and smooth graduation between the sections, which is hardly noticeable. These are widely used for students and office workers, so that they can view near objects such as books or paperwork and still see computer screens (most commonly set at an intermediate distance) with one lens. 

 

Multifocal lenses (also knows as Progressive lenses): Multifocal lenses have three sections  – Near, Intermediate and Distance. They do have some distortions out in the peripheral sections on both sides of the lens, however large advancements have been made over the last few years to eliminate this and it is much better than it ever used to be. The lenses physically look like a single vision lens, with no noticeable sections to be seen. The pro’s of this type of lens is once you find the right design, you should be able to put them on in the  morning and do anything in them. The Eyewear Girl Face a Face hello 2The down side, is if you get motion sickness, or have someone dispense them incorrectly (happens WAY too often unfortunately) you may have issues adapting. But don’t let that dissuade you from trying them; there are non-adaption warranties with every lens manufacturer I have ever dealt with but of course, you will need to discuss this with your Optometrist before purchasing. Don’t give up, they’re worth adjusting to but also don’t keep quiet if you’re finding it difficult. There are plenty of options out there and your Optometrist can’t help if they don’t know there’s a problem.

 

So, that is a VERY basic run down of the main types of prescription lenses. On top of the above, each of these lens types come in different materials, with many coating options and most can be designed using many measurements of where your eye sits in the frame you have chosen and takes your unique prescription into account as well.

As mentioned earlier, this is your Know what you’re buying class #1, there will be plenty more with more info on everything, but please don’t hesitate to ask any questions below!

M.