Today we are talking about the special set of conditions that you are in when the doctor is giving you your refraction (which is your eyeglass prescription).
Your eye exam, you’re sitting in a dark room and you are looking through a phoroptor which is 12 millimeters away. The lens that you are looking through is made out of glass (index of refraction of 1.53) and it is also non-glare treated (so it has anti-reflective coating). Those are very specific conditions and the higher the prescription is, the more likelihood that the optician who is making your eyeglasses, if it’s even an optician, your eyeglasses are not going to reflect the special set of circumstances that the prescription was written in.
What I mean by that is that it’s not compensated!
So, to them, they are taking your eyeglass prescription (and so they’re order takers) and they are going to fill in the blank and type in that same exact prescription; but in reality, it is not going through a calculation which it will compensate for new conditions of the eyeglasses when they are sitting on your face.
Not all glasses are going to sit exactly the same distance away from your eyes. If they have nose pads they’re going to sit further away. If they don’t have nose pads because they are acetate then they’re going to be much closer to your eyes and that affects the total prescription that you’re going to wear.
If you have a +5.00 Sph prescription and the glasses are going to sit further away, that means that that +5.00 Sph is going to be a stronger total strength than what the doctor wrote. So your prescription is already wrong to begin with.
Or, if it (the eyeglasses) is closer, then that means that the prescription is going to be less and therefore it’s going to be wrong and it’s not going to be what the doctor wants you to have under those specific conditions when your refraction was taking place.
So, keep this in mind because it is a little confusing but this is called a compensated prescription and free form digital quality lenses are what we do, which we take that (compensated calculations) into consideration.
Here, we dive even deeper into compensating the prescription. It is not just about the prescription by itself. It is also about how the measurements are taken. If you notice the accuracy, this is 1/10th of a millimeter in accuracy.
Also, the wrap angle:
that describes the face form or the curvature of the frame. Not all frames have the same curvature.
This one has a lot of wrap (pointing to a sports sunglasses). This one does not (pointing to a frame with a flat front). This one is a very flat frame.
The prescription has to reflect the wrap of lack of in each frame.
So, if you’re getting three different pair of glasses,
You will have three different set of wrap measurements (or face form measurements).
Not every pair of glasses is going to fit you the same way. The pantoscopic tilt will differ depending on how high or how low your ears are.
A good example is the Ray Ban Wayfarer the Classic Wayfarers, they have a very steep pantoscopic tilt. When you get three different pair of eyeglasses, you’re going to have three different pair of pantoscopic tilt measurements and that has to be included and customized when you’re getting glasses.
Most people don’t factor that in. So, when I make you the glasses, I’m going to make you the most perfect pair of glasses because I’m going to factor in all of these detailed measurements:
Wrap angles, pantoscopic tilts, vertex disctance, and more.
Vertex distance is how far away the lenses are from your eyes. Whether they have nose pads or whether they don’t have nose pads, that is going to vary quite a bit (the vertex distance).
The measurements that I take are exact anatomical measurements based on your anatomy not my opinion as to where the elevation should be on your optical height or your progressive lenses.
A lot of people are not perfectly symmetrical, so one eye might be a little higher than the other. That is going to be reflected on your prescription lenses. Every single little thing about the way your face structure is going to be reflected on your measurements. All of this is really important.
We had one person come in one time and they said (after they were seeing amazingly great with these glasses). So they came back and said, “oh Jairo, my doctor said one of my seg heights (optical centers) is higher than the other”.
And I said, “they probably are, please come in so I may show you why”. And sure enough, we went back to the measurements and you could clearly see that the optical center was one higher than the other because one eye was higher than the other.
So, everybody else (other opticals and doctors) likes to make things equal when they are NOT.
We make the glasses absolutely perfect. Compensated measurements based on the accuracy of 1/100ths of a diopter and the measurements are taken at 1/10th of a millimeter in accuracy.
Alright, have a great day!