Thursday 20th June 2024

A DO's desk

The whole reason most of us wear glasses prescribed or non-prescribed are the lenses. Spectacle lenses are available in "glass" and "plastic" to a lay person. Glass lenses have almost become so rare that we are not going to write about it here.
Single, double of multi focal
The question to ask here is, why are you buying a pair of glasses and what is the working distance? For example, if you are requiring glasses to read, then the working distance is where you hold your reading material, and this usually is within 35 to 45cms. So, the pair of glasses should match this single area and you should choose a single vision lens. If the working distance moves further away from your eye and within 75 to a 2 or 3 metres then it is classed as Intermediate. Anything further away from 3 metres will fall into a distance prescription category. At Specsonweb, you have the option of choosing what working distance you need your glasses to work for and we will work out the prescription you need from the Eye Test results you have up loaded. (Note - only applies to those who are a Presbyope and have a separate reading addition).
If you need to look far (more than 3 metres) and look at the reading (35 to 45cms) then you have two or more working distances and you will need either bifocal or multifocal lenses.
The way to identify this from your Prescription or Eye test results, is by looking for an ADD number or if they have written the prescription in the Near or Reading section of the prescription. Optometrists also would have mentioned this to you and written or ticked off in the recommendations section.
At Specsonweb, we ask you to note this down and as part of our order acceptance process, we call or email you to ask these additional questions.
Thick or Thin
In the "plastic" lens category, we have different refractive indices and this is the way the lens is measured. The refractive index is a measurement that tells us how much the light is bending through the surface of the lens.
Now the most common refractive indices in "plastic" lenses are 1.498 (standard), 1.54, 1.59, 1.6 (level 1), 1.67 (level 2), 1.74 (level 3). The levels in bracket denoted the Specsonweb categorisation of the types of lenses. The main thing to remember from this is that the higher the refractive index the thinner the lens. So, if you have a higher prescription, this means the lens thickness also increases. Therefore, it is recommended to choose a lens with a higher refractive index, so the finished spectacle lens can accommodate your prescription and at the same time be comfortable to wear.
It is worth noting that, we have not talked about different surface treatments on a lens in this blog and will cover the coatings in a separate post.