When it comes to brass tacks, the choice of prescription lenses for your new glasses most often boils down to how much you’re willing to pay to reduce weight upon the bridge of your nose: Opt for the cheapest eyeglasses lenses and you’ll have also opted for the heaviest lenses; lenses which may not have anti-scratch or anti-reflective coatings to boot (these ‘nice to haves’ usually come as standard on more expensive lens packages).
Lens indices: Thickness & weight.
These days glass lenses eyeglasses are a thing of the past having been replaced by plastic lenses which although lighter than glass is not necessarily much lighter in the case of cheap plastic lenses. Many customers still approach their opticians seeking “sunglasses with glass lenses” while looking for prescription sunglasses with modern (plastic lenses). For clarity then this article shall be confined to considerations of modern lenses only. Lens thickness/weight is described by one of four lens indices: 1.5 index is the thickest and heaviest, while 1.61, 1.67 and 1.74 become progressively lighter and thinner (as well as progressively more expensive) as the index value increases in magnitude.
While the one might find one’s self swaying towards the very thinnest and lightest lenses every time (ie. 1.67 and 1.74 indices) these are not recommended for rimless & semi-rimless frames for practical reasons to minimize the risk of chipping and/or cracking. That said, sometimes a choice of thick and heavy lenses suits some people just fine. There are some trade off’s to be made, the final choice will ultimately be the consumers so following general advice should help you make an informed decision:
Have you chosen rimless or semi-rimless frames?
We recommend a 1.6 index lens for rimless and semi-rimless frames because these are more resistant to chipping and cracking. One could opt for the 1.67 and 1.74 anyway but be warned: While these glasses are very light on the bridge of the nose, they must be treated with extreme care to prevent damage. For lenses of these indices risk of chipping and cracking is increased from ‘could happen’ to ‘chipping and cracking is highly likely’. Furthermore, should you decide to disregard this advice and opt for 1.67 or 1.74 you probably won’t get the usual one year guarantee on your lenses from most opticians. Often, they’ll only guarantee the bridge and the temples under these circumstances so if chipping or cracking does occur you will not have recourse to refund or return – ouch!
Thick frames vs. thin-delicate frames lens-choice debate:
Thick eyewear frames will hide a thick lens quite well but that same thick lens will definitely be more noticeable if placed within a thin, delicate frame (so we advise you to be careful of this fact and take note!) Thus for thin frames, a thinner lens will certainly be the more aesthetically pleasing choice.
However (getting back to thick frames for a second), should you opt for thick frames and thick lenses, you will have a pair of glasses that are going to feel heavier on the bridge of the nose which may not be very desirable.
Lastly, if you choose a thin & delicate pair of fully rimmed spectacles you can safely opt for any of the higher (lighter-weight) lens indexes without fear of cracking or chipping during normal usage for a pair glasses that will feel very light on the bridge of your nose. Your choice of the index depends upon budget and upon how light you want your glasses to be.
A Quick Overview of lens types – you’ll have to choose one!
(1) Distance Lenses: Choose these if you use your glasses all day but do not have bifocals or varifocals. These are general-purpose lenses intended to be used for everything from reading to driving and (at risk of laboring the point through repetition), are usually worn all day.
(2) Reading lenses: Choose these if you want glasses specifically for reading documents and seeing things very close to you or at arm’s length away including computers, sheet music, documents, etc
(3) Enhanced reading: These lenses are specialized: Only choose these if they have been specifically recommended by your optician.
(4) Bifocal lenses (with a line): Choose if you’ve had them before, you liked them and your optician recommends them. Read more on the bifocal lenses below.
(5) Varifocals: Choose if you’ve had them before, you liked them and your optician recommends them. Read more on the Varifocal lenses below.
Distance Lenses:
These are the most common lenses of all; they’re usually worn all day and can be prescribed for both long and short-sightedness. When choosing lens types on glasses websites you may see the word ‘distance’ used interchangeably or in conjunction with the term ‘single vision’ and may see (for example)
Distance (single vision)
Reading (Single Vision)
You’ve guessed it, these are corrective lenses for short and long-sightedness respectively.
Bifocal Lenses:
These lenses contain both distance and reading prescriptions in one lens. They’re easily recognizable by a horizontal line that runs through the middle of the lens. Although they’ve been overtaken in popularity in recent times by varifocal lenses, they nonetheless still retain notable popularity as they remain a very cost-effective lens solution. There is a however a very noticeable jump between reading and distance parts of these lenses.
Progressive or Varifocal Lenses:
These lenses also known as progressive lenses, contain distance, intermediate and reading prescriptions all in one lens. The transitions between each of the prescriptions are very smooth in contrast to bifocal lenses which have a noticeable jump. There are no visible lines on a varifocal lens but the segment containing the reading prescription is just about visible as a semi-circle. In the old days, there was some noticeable distortion present at the right/left extremities of varifocal lenses which often made the wearer feel a little seasick. Thankfully these days have gone with the evolution of free form varifocal lenses that are now very easy to wear.
Varifocal lenses include corrective prescriptions for all of the following vision ranges within a single lens:
i. Distance
ii. Intermediate
iii. Close-range
Note: if you buy these lenses from an online seller, they will require a varifocal prescription and very accurate papillary distance [PD] measurements for each of the above ranges. For this reason, we do not recommend PD measurements are taken at home for varifocals lenses: The required accuracy of PD measurements for varifocal prescriptions is such that nothing less than professionally measured PD measurements will suffice. In this particular case, an optician must take the PD measurements for you.
Transitional lenses:
Also known as Reactions, Photochromic and Sun sensors, these lenses darken in response to increasing levels of U.V. light and can be ordered in either grey or brown tints. They tend not to work at all in your car: car windscreens tend to block the U.V. light these lenses need to sense to darken.
Enhanced reading lenses:
These provide a greater depth of focus than conventional single vision lenses for reading. Also known as office lenses, the top half of the lens will have a longer focal distance at the top and closer at the bottom. As the term “office lens” implies these have been developed for use with the VDU although have other applications such as for use with reading music or DIY. Like a varifocal lens, they have no line but will give a much wider field of vision for the intermediate distance. They have a little or no distance vision and are not suitable for driving.
Scratch-resistant coatings:
These days, all lenses are made of plastic and not glass. Left without scratch-resistant coating, this plastic remains soft and scratches easily. A scratch-resistant coating is not a coating in a similar sense to a coat of paint but is rather a process where the plastic surfaces of the lens are toughened to make them more scratch-resistant. While this process will not make your lenses scratch proof, it makes them a good deal more resistant to picking up scratches during normal use. We would advise that scratch resistance is very nice to have featured on your lenses.
Anti-reflection coatings (a.k.a. MAR / anti-glare coatings):
This coating reduces reflection on the outside of the lens so that when people look at you they will not see a glare or reflection from your glasses lens surfaces. Instead, your lenses shall be 100% transparent and glare-free to the onlooker. As such they are therefore aesthetically more attractive than non-coated lenses. Anti-reflect coatings also reduce the glare coming into your eyes from PC’s, or the headlights of on-coming cars at night.
Tinting:
All prescription lenses can be turned into sunglasses by choosing tinting options. It is possible to choose a homogenous tint which will make the entire lens the chosen color or else choose a graduated tint where the lens is darkest on top while getting progressively lighter towards the bottom.
Polarizing:
Glare is caused by light reflecting off of surfaces and horizontally bouncing into the human eye. Polarizing tinted lenses will ensure that only vertical light can get through thereby eliminating glare. The polarization of lenses usually incurs an extra charge.
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