It is important that when we make your spectacles that the optical centre of the lens sits in front of your pupils. This will give you the best vision possible.
Pupillary Distance - PD
For every pair of spectacles this means we need a measurement usually referred to as your PD, which stands for Pupillary Distance. This is the distance between your pupils measured in millimetres. For most people this will be in the range of 56-70mm. It would be unusual (but not impossible) for an adult PD to lie outside this range.
Although we are measuring the distance between the centre of your pupils this is quite difficult with a ruler so we actually measure the distance from the outside of the iris in one eye to the inside of the iris in the other eye. The contrast between the coloured part of your eye (iris) and the white part (sclera) make it easier to measure and the distance is exactly the same.
Once you are an adult and have stopped growing this measurement will stay the same. We can get this information in several ways.
1- Your Optician may give it to you. It is not normally written on the prescription and you may have to ask. In most cases Opticians are happy to supply this although they may make an extra charge for it.
2- We can measure it from a previous pair of spectacles. If we are reglazing your frame simply send it to us as requested and we will take the PD measurement from these. We can tell if they are distance, reading or otherwise.
3 - Send us a photo of yourself wearing your current spectacles, straight on to the camera and as big as possible and we have software that allows us to measure the PD from the photo. In order to do this we need to know the size of your frame. This will be written on the inside, usually inside on of the sides but occasionally inside the bridge. It will be in the format of 53/16, 49/20 etc although it may be written as 50 (small box) 17. (I cannot reproduce that here.) Send it to firstname.lastname@example.org labelled with your name and the size of the frame and we will email you back your PD.
4 - It is possible to measure this yourself or with the help of a friend using nothing more than a ruler, (and a flat mirror if doing it yourself) using the following procedure. Don't worry we have a good idea of what your PD should be and we will query anything that doesn't look correct.
5 - If you have a fairly normal prescription we can use an average value for a man or a woman based on thousands of previous measurements. It is always best to use methods 1,2 or 3 but unless you have a high prescription an average PD will normally be ok.
Measure your PD
1- Looking into a mirror place the ruler flat along your forehead so that the edge is just above your eyes. Line up the end of the ruler with the outside of your iris in your left eye.
2- Without moving the ruler, now look at your right eye and measure to the inside of the iris. This measurement in mm is your distance PD. Your eyes will move to refocus on your right eye and the left eye will not now line up with the end of the ruler. This is normal.
Most normal rulers will be upside down, if you are having trouble reading the ruler you could try it by placing the ruler the correct way up on your nose but be careful to keep the ruler straight. In this case the PD is 63mm.
Make sure you are directly in front of the mirror and looking straight ahead.
This takes a bit of practice but this method is how I have taught probably hundreds of members of staff how to take a PD. We suggest taking three measurements and using an average value. Get a friend to check if you are unsure.
Your distance PD will be different to your near PD as when we read our eyes rotate inwards slightly to allow us to focus on an object that is close to us. This means your near PD will be smaller than your distance PD. We will calculate your near PD from your distance PD exactly the same way as your local Optician would do.
Bifocals and Varifocals
If you are ordering a Bifocal or Varifocal lens we need an additional measurement in order to determine where to set the segment for a bifocal or the centre of the distance vision for a varifocal. This normally referred to as the Height.
If we are reglazing your old spectacles we can take this directly from your old pair and nothing more needs to be done. However if you are ordering a new pair we need to see the new frame on you as this measurement depends on where the frame sits on you. In order to do this after we have received your order we will send you the frame. We then need a photo like that requested above for the PD measurement. (We can do both from the same photo) Send it to email@example.com labelled with your name and we will then order the lenses. The lenses cannot be ordered before we get this measurement as it helps determine which size of lens we need. Then return the frame to us in the pre-addressed bag so that we can put the lenses in.
We do not need heights for distance, reading or intermediate lenses.
These two measurements are all we need to make any pair of spectacles and are exactly how your local Optician would do it. If you have any problems please contact us on firstname.lastname@example.org