Rimless Frame Mount and Contact Lenses Addition
Q: Hi! I'd like to ask you a few questions on two different matters:
1. I have an uncut pair of -3.25 diopter Zeiss (PhotoFusion, Duravision Platinum coating) plastic lenses, 1.5 refractive index.
Can they be mounted on a rimless frame (taking in consideration that they are quite thick due to this diopter value)? Is it risky to assemble this kind of frames on the lenses I’ve mentioned, as they say that while drilling the holes for the plugs, the lens can crack?
2. How is the addition on the contact lens working? When is the low addition used and when is the high one used on a myopia contact lens, in relation to early or advanced presbyopia?
For instance, a +1 low addition makes the -3 diopter of the contact lens like a -2 diopter on that specific area of the lens, respectively a +2.5 high add. makes the same -3 diopter like a -0.5?
Thank you in advance for your answer,
A: For the first question
As you know and see, the (-) lenses are thin in the middle and thick on the edge, and the thickness is diminishing from the edge to the center.
The rimless frame has screws that go through the lens, so there is a maximum thickness accepted for this kind of eyeglass. But the good news is that they will not mount the lenses on the edge where is the maximum depth.
The lens will be shaped and become smaller and thinner. So my advice is that you should choose a smaller frame, so the screws go in the glass in the thinner part and this way it should be ok.
For the second question
I'm not sure I understand the question correctly.
For example, if you mean a multifocal contact lens that has multiple diopters, then the lens has all the diopters without intersecting one with each other, so you have -3.00, then -2.75, -2.50. And so on from the center to the edge of the lens, and the addition is decided with an ophthalmologic consultation. This lens helps you see far and close.
If you mean that you have contact lenses for far vision, and want eyeglasses to put on with the contacts in your eyes, then you are right. The calculations are made the way you described, and you will have (+) diopter eyeglass that compensates your presbyopia so the total diopter will be the sum of the two diopters. Because one is (-) and one is (+), the total will be your close vision diopters.
Hope this helps