We realise that when you’re buying glasses online it can at first seem like a bewildering experience. We believe that customers should receive guidance in how to do this correctly and that’s why we have produced this guide to purchasing glasses online.
This guide will assist you in avoiding pitfalls and help you to decide upon a frame and lens that will give you good vision, be comfortable and look great too.
HOW TO CHOOSE A FRAME THAT FITS...
Frame sizes are usually in the format of “51 - 16 - 135”. In this example this means that the lens diameter is 51 mm, the bridge is 16 mm and the side length is 135 mm.
• The first number is the lens diameter
The size of your frames can affect the look of the glasses on your face and how comfortable they are to wear:
• The top edge of the frames should not be higher than the line of your eyebrows and look good if they follow the same shape.
• The lower edge of the frames should not sit on your cheeks, (even when you smile!) so that they don't rub or irritate you.
• The width of the frames should not be wider than the overall width of your face at the temples.
• The scale of the frame should be in proportion with you - If you are petite, don't choose large chunky glasses.
If you want to compare the width of some new glasses with your own glasses the easiest way is to compare the total width. The total width of the frame is the horizontal lens diameter x2 added to the bridge distance.
For example, for the frame described above
56 X 2 = 100 + 17 = 129mm
Each of the frames on our website show these measurements in millimeters and the total frame depth in millimeters. You can compare these to your current frame using the method above.
IDENTIFY THE FRAME YOU WANT...
Have you spotted a friend or work colleague wearing a frame you really like?... Perhaps you’ve seen your 'must have' frame in another shop but you want to buy it online with Eyewear Heaven.
With our simple ’How To’ guide you will be able to confidently identify the brand, model, colour code and size of the glasses you want.
Using this information on our site you will be able to find the exact frame you want.
Your prescription may seem a little confusing at first glance but it really is quite simple to understand.
Firstly, every prescription follows the same format wherever you are in the world. There may be a few variations and abbreviations and our guide will explain those later, let’s describe what it all means first.
Each prescription will have a right and left value for the correction of your vision within the following boxes:
• ‘SPH’ (sphere).
This is the correction for long or short sightedness and is measured in dioptres. It will consist of a ‘+’ or ‘–’ power in 0.25 steps. Eg. -0.25, -0.50, -0.75, +1.00, +1.25 and so on. Unless 0.00 or plano is prescribed which means no power.
• ‘CYL’ (cylinder).
This is the correction for astigmatism, which also has a direction or ‘AXIS’. This may consist of a ‘+’ or ‘–’ power in 0.25 steps. Eg, +0.25, +0.50, +0.75, -1.00, -1.25 and so on.
The AXIS will be specified as a numerical value from 1 to 180 and represents the direction in which the CYL power acts, BUT, this is only specified when you have an amount of CYL correction.
Sometimes a ‘Near Add’ or ‘Addition’ will be included in your prescription. This is usually for people over the age of 40 or for people who have a high near usage, causing eyestrain such as VDU operators. Your Optician may also prescribe an ‘Intermediate Add’ if you are a VDU user.
The ‘Near’ or ‘Intermediate’ add will always have a ‘+’ value. (Just think, it adds power.)
In some rarer cases ‘PRISM’ and ‘BASE’ are used for the correction of muscle balance problems. If your prescription has this then you will need to have your PD measured professionally.
When buying glasses online you can select your prescription from the drop down boxes so you can simply copy the details you have on your written prescription.
Do not fall for this most common mistake!
The single most common mistake when entering prescriptions online is selecting a ‘+’ value instead of a ‘–’ value or vice versa.
Your prescription may consist of both ‘+’ AND ‘–’ Values. For example: +1.25/-2.50X147. Usually opticians will write the ‘–’ and ‘+’ signs above the value.
Some opticians will write out your complete reading prescription underneath your complete distance prescription. To calculate your ‘Near Add’ you subtract the distance sphere value from the near sphere value. For example:
Therefore, the Near Add is: +4.50 - +2.00 = +2.50
Some common abbreviations...
• PLANO, 0.00, INFINITY - All mean the same thing… nothing. No power or correction is needed.
• DS (Dioptre Sphere) - This refers to the amount of power being prescribed to correct and long or short sightedness. If DS is written in the CYL box this indicates that there is no astigmatism (No CYL value). It‘s a way for the Optometrist to note that he/she has not forgotten to include the CYL prescription, there simply isn’t any!
PD (Pupillary Distance) - is the distance between the center of one pupil to the centre of the other in millimeters. It is probably worthwhile to take a moment to explain a little more about your PD because this mesurement has caused much debate in the dispensing of glasses online.
Opticians generally do not give this to you because this is considered to be a dispensing task, so it will only be measured when you’re buying glasses from that particular optician. In most cases, except for those with particularly high prescriptions, we can use our experience and certain criteria such as your gender and the size of frame you have chosen to determine a PD, measurement for you. Your optician can measure this for you, however it is quite simple to measure your own PD.
The best way is to have a friend help you. Look at a point in the distance whilst your friend takes the measurement in millimeters. It is easier and more accurate to measure from the limbus to limbus (the limbus is where the white part of the eye meets the coloured part of the eye). This will give you the same measurement as measuring from the center of the pupils as the high contrast boundary is easier to see.
Both of these methods of measuring your PD will give you the same value.
CHOOSING THE CORRECT LENSES...
Lenses come in many types and again at first, things can become a little confusing. But don’t worry. We’ll explain your options in detail so that you can understand and choose the best lenses for you.
Firstly, lenses can be made in two materials Organic (Plastic) or Mineral (Glass). Most lenses sold today are of the plastic variety as they are far lighter than glass. In some rare occasions when extremely thin lenses are required for very high prescriptions glass can be the best option. We only sell glass lenses through our practices.
Each lens has a ‘Refractive Index’. The way in which the refractive index is calculated is not important at this time. What is important is what it means to the thickness of the lens.
Most people think that when we talk about a “1.6 lens” this means it is going to be 1.6mm thick but it actually means that the lens has a refractive index of 1.6.
Basically, the higher the refractive index the thinner the lens will be. This is because materials that bend light more than others have a higher refractive index and hence a shorter or longer ‘Focal Length’. This means that the same correction and focal length can be achieved from less lens material making them thinner.
Here is a key to choosing the best lens:
• Standard Plastic CR39 (1.5) - We use this material for our standard lenses, which is suitable for many prescriptions. However, prescriptions with powers stronger than +3.00 and -3.00 may start to look thicker on the edges for a minus lens or thicker in the middle on a plus lens.
There are also many different styles of lenses. Lenses for single vision correction e.g. distance or reading, to Bifocals and Varifocals for the correction of both distance and reading within one pair of glasses.
We only provide single vision lenses online, multi-focal lenses are available through our practices.
Varifocals (Practice order only) - Varifocal glasses blend gradually from your distance vision through your intermediate and in to your reading vision. This means that the lenses have to be accurately measured and aligned perfectly with your pupils.
Bifocals (Practice order only) - Bifocals are basically distance glasses with a reading segment in the bottom due to the fact that there is no gradual phase. Bifocals have a far wider area for reading than Varifocals but have no intermediate correction.
There are also various types or ‘shapes’ of the reading segment. Typically the standard is the ‘D-Seg’. This looks like the letter D on its side with the flat part it the top hence the name. There is also a ‘Round-Seg’ in various sizes and ‘Executive’ or ‘E-Type’ bifocal where the whole bottom half of the lens is dedicated to reading, great for people who do a lot of reading at work using plans etc.
Single Vision - These lenses can be used only for distance, intermediate or reading hence the name ‘single vision‘. However, some people who are slightly short sighted (’-’ Power SPH prescriptions) will be able to read without their distance glasses.
Single vision lenses are available in both plastic and glass materials and in all index’s.
Tints - Tints can be used to turn ‘Plastic’ lenses in to sunglass lenses. They are available in many colours. However, 1.67 and 1.74 single vision lenses cannot be tinted as they already contain an Multi Anti-Reflection Coating (MAR) to reduce ‘Power rings’ and protect the lens from scratches. High index materials are actually softer than standard and this is why they need protection.
Photochromic - Photochromic lenses are usually referred to as ‘Reactolite’ which is a brand name for the glass variety or ‘Transitions’ which is a brand name for the plastic variety.
Basically they do the same thing. These are lenses which are clear indoors but then react to UV (Sunlight) and transform into sunglasses.
As photochromic lenses require UV light to change, if you use them behind a car windscreen they will not work as effectively as normal due to the windscreen filtering out some of the UV.
Polarized - Light reflected from surfaces like a flat road or smooth water is generally horizontally polarized. This horizontally polarized light is blocked by the vertically oriented polarizers in the lenses filtering out glare and allowing you to see below the water line. Available in grey or brown polarized lenses are ideal for fisherman and also for drivers.
Usually an anti-reflective coating is referred to as an "MAR" (Multi, Anti-Reflective Coating). There are many benefits to a MAR. Firstly, they are far more aesthetically pleasing as they reduce the amount of light reflecting off your lenses especially when having your photograph taken. Other benefits include:
• Reduced glare when driving at night
• People can see your eyes and not a patch of light
• They filter out reflections from computer screens
• Reduced ‘Power rings’ (visible rings on the lens in high prescriptions which is caused by light constantly bouncing back and forth within the lens due to total internal reflection.
• Provides UV protection
• Anti-Static which aids lens cleaning.
A FINAL NOTE...
The internet is reaching further and further into our daily lives as more and more products become available online. Never before have you had the choice of ordering your glasses in a practice OR in the comfort of your own home.
We hope that you’ve found the guide useful and that it will help you to select a great pair of glasses.