Buying Prescription Glasses Online Guide – Nuspecs

Buying Prescription Glasses Online Guide

Buying prescription glasses online can seem daunting but it’s easier than you might think. There are two basic components to consider – the frame and the lenses.


Choose Your Frame


The first step to buying prescription glasses online is to choose the frame style that appeals to you. The design of a frame can either be full rimmed, semi rimless [often referred to as supra] or rimless. Each design can come in a variety of shapes, materials and colours. In general plastic frames will give the wearer a bolder look, whereas metal frames are generally more subtle.

The basic rule for selecting frames is that shapes should be selected that are opposite to the shape of the wearers face


For example:


Oval Face – Choose frames that are as wide or slightly wider than the broadest part of the face.


Oblong Face – Select frames that are deeper in size rather than width


Round Face – Choose angular shapes frames that will lengthen the face


Square Face – Select frames that are wider than the widest part of the face and not too deep


This list is by no means definitive and you should always choose frames that you feel reflect your own individual style.


Glasses Frame Dimensions


There are three size details to evaluate when choosing your frames. If you look on the inside arm of a current pair of glasses you may see some figures set out for example like this:




The first number refers to the ‘Eye Size’ or ‘Lens Diameter’ of a frame. This is the diameter [taken along the middle horizontal] in millimetres [mm] of one lens shape. It is not the total width of the frame.

The second number is the ‘Bridge Size’. Again taken through the middle horizontal this refers to the length in mm between the rims of each eye size

The last number refers to the overall arm length in mm usually measured from the screw to the end of the tip.

What The Numbers On Your Glasses Prescription Mean?

After selecting your frame, you now need to order your lenses. Before doing this please take time to study and familiarise yourself with the prescription you have been given by your Optometrist. This may make things slightly easier when selecting lens options etc. A typical prescription might read:


SPH (Sphere) is measured in "dioptres" and shows how long or short sighted you are. If you are long sighted the number in the sphere column will have a plus "+" before it. Conversely if you are short sighted the number will have a minus "-" before it. 


CYL (Cylinder) is a measure of the amount of astigmatism (distortion) that needs to be corrected for and is also measured in dioptres. Again the CYL value can either have a “+” or “-“ before it.


If you do not have any astigmatism the CYL and the AXIS boxes will be blank. Occasionally an Optometrist will enter ‘DS’ in the CYL box to indicate no astigmatism.


AXIS gives the direction of the astigmatism and is measured in degrees.


PRISM corrections are sometimes needed to balance the eyes so that you use them both together. An imbalance can occur when one or more muscles in one or both eyes become weak.


The NEAR ADD is also measured in dioptres. This is the value added to the SPH of a distance prescription to achieve a reading prescription when necessary. A NEAR or READING ADD is usually prescribed to someone who is PRESBYOPIC. 


PRESBYOPIA is a condition that starts in your forties and ultimately affects everyone. Its symptoms are blurred vision when reading or doing other close work where previously there was no such blurring. This is caused by a loss of elasticity in the muscles that operate the lens in the eye. It is typically characterised by people with normal vision having to hold newspapers at arm's length in order to be able to read them. Presbyopia can be corrected with bifocals, varifocals or single vision reading glasses.


Some Optometrists may write out a reading prescription in full, rather than just entering a reading ADD.


Intermediate vision is calculated when the wearer wishes to view objects that are not necessarily close to or far away. Typical examples of this are viewing VDU screens, reading music or cooking on a hob. Some Optometrists will enter an INTERMEDIATE ADDITION onto the prescription. Again, this is added to the distance SPH to calculate the intermediate prescription. If there is no intermediate ADD on your prescription, and you want to order intermediate glasses, enter your Reading ADD and a qualified Optometrist should be able calculate the Intermediate ADD measurement for you.

Choosing Your Prescription Lenses

Once you have familiarised yourself with your prescription you now might like to consider selecting your lenses. Before doing so please consider carefully what you want your glasses for i.e. DISTANCE, READING, INTERMEDIATE, BIFOCAL or VARIFOCAL.

When you have decided what you would like your glasses for, enter the values from your prescription into the prescription form provided onto the website.  Many sites also offer the option of uploading your prescription via file or jpg – this can often be the best method because it minimises the risk of details being incorrectly transposed.  If you are entering your prescription details manually please ensure you do this accurately and take time to check and double check that the numbers have been entered correctly. PLEASE ALSO ENSURE THAT YOU HAVE ENTERED THE CORRECT SIGN FOR EACH VALUE WHERE APPROPRIATE i.e. “+” OR “-“  


Pupillary Distance (P.D.)


This measurement is sometimes required to ensure maximum visual comfort when looking through your lenses and is simply the measurement in mm between the pupils of the eyes. If the Optometrist has not written your PD on your prescription it is generally advisable to leave this blank or seek advice – if a PD measurement is not known the industry average measurement of 63mm is then typically used to calculate this.

Prescription Lens Types

A standard lens is a plastic lens [often referred to as 1.5 or CR39]. It can also be Anti Scratch and Anti Glare coated [see later] and can also be easily tinted for sunglasses. For a low cost entry product, this lens is ideal for most single vision prescriptions up to approximately + or – 4.00 SPH. However, a thin and lightweight 1.6 lens might be considered if thickness and weight were issues for the wearer

For prescriptions between + or – 4.00 SPH and + or – 6.00 SPH it may be worth considering a 1.6 thin and lightweight lens type or thinner be selected. This option not only gives the wearer a more comfortable experience, the glasses will also look more cosmetically pleasing. These lenses often come as standard with an Anti Scratch & Anti Glare coatings.


Lens Coatings


Anti Scratch


All lens material is prone to scratching, even glass. However, applying an invisible hard coat treatment to the back and front of the lens does provide protection on a day-to-day normal use basis. Please be advised that if you drop your glasses onto a hard surface they will still scratch.


Anti Glare


Lens reflection can be a major problem for glasses wearers. Driving at night, watching television and operating computers are just some of the many situations where the spectacle wearer has to put up with annoying and distracting reflections.

All these reflections can reduce the amount of light reaching the eye by as much as 15%. Which means both vision quality and contrast are impaired. Because the reflections cause a mirrored effect on the front of the lenses the eyes can be unflatteringly obscured and even the most stylish frames look less attractive. By treating the lens with layers of a special metal oxide coating reflections can be limited to less than 2% and the problems are eliminated altogether. Because Anti Glare lenses give such a dramatic reduction of reflections the benefits are tremendous; suddenly the lenses provide much clearer and sharper vision - about as close to natural vision that glasses wearers can get. The mirror effect often seen by onlookers is virtually eliminated which means the wearer's eyes can be seen more attractively. Drivers can really see the benefits when driving at night as reflections from headlamps and streetlights are kept to a minimum.

An Anti Glare coating often comes as standard with Anti Scratch.


Light Reactive/Photochromic Lenses


Photochromic lenses change from lightly tinted when indoors, to sunglass darkness when exposed to the sun’s UV rays. Advanced technology means that the lenses adjust quickly to changing light, so that the wearer sees more clearly and comfortably in virtually any light condition. 



Prescription Sunglasses Tints


A permanent ‘sunglass’ tint typically offered in dark grey or brown. The lenses are darkened to a 15% transmission, meaning 15% of the light is transmitted through the lens.




Buying Prescription Glasses Online is a straightforward process.  If you have any specific requirements or issues it is always advisable to consult with a qualified Optometrist.


If you have any questions or would like more information about ordering your prescription glasses online please do not hesitate to email us at or speak to one of our advisors on 0330 223 1026 – we will be happy to help.



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