We've gone over picking frame shapes for your face, and possible frame materials, but what makes a good frame choice for your prescription?
You may think its simply a matter of "I like this, lets make it", but there are certain things to consider when you have limitations based off of your actual glasses prescription!
First off some lens basics.
If you h
ave a prescription that starts with a + sign, you will find that your lenses will be convex, therefore the thickest area of lens will be the optical center of the lens. However, if your prescription starts with a - sign, you will need a concave lens, which will have its thickest area at the very edges of the lens, making the optical center the thinnest area of the prescription lens. Most of the limitations will have to do with how strong the prescription is itself.
Lens thickness
Of course there are different thicknesses of lens, which your optician will be able to recommend the best 
option for your prescription, although some frame choices may also determine which lens is used. Lenses will come in what we call indexes - the lower the index number, the thicker and heavier the lens will be. A 1.5 index lens is the most basic and thickest of them all, a 1.6 is the next step up and has the best optical value of all the lens indexes no matter what your prescription is. Both of these plastic lenses will be used in a more minor prescription, but if you have a stronger than average prescription, you may want to choose something even thinner and lighter which would be a 1.67 or a 1.74 (for the really high prescriptions), but of course your optician will be able to recommend the best index of lens for your prescription.
Low to Mid Strength prescription
If your prescription is fairly minimal, you will usually be fine in a 1.5 index lens as long as the frame you choose is also appropriate to this lens. Anyone who's prescription is +/- 2.50 and up you would certainly want to consider going into a 1.6 index lens. Either of these lenses will work with a low to mid range prescription, depending on your frame choice, and will work well in almost any frame size and shape.
Higher prescriptions
Once a prescription gets up in powers, you will start to have more limitations in your frame choices. There are certain shapes and styles that may work better for your prescription lenses than others. For example, if you have a very high + prescription, you will need to pick a smaller eye size frame, and
ideally something more rounded. This will not only help cut down on weight of the lenses itself, but will help to bring down any fragility in the thin edges of the lenses. Depending on how high your plus prescription is, it may not even be possible to cut lenses if you choose a frame with an eye size too large, as the thin edges will get just too thin as the eye size gets larger. On the other hand, if you have a high minus prescription, you would be more advised to choose some kind of plastic frame if you like them, because the thickness of the plastic frame will help to hide any additional edge thickness you may have. Of course, the bigger the lens gets, the thicker the edges will be, so choosing a frame on the slightly smaller side will benefit your lens thickness and weight as well in this situation. If you are a very high minus prescription, its a good idea to consider a frame that has some rounded edges to it, as the severe angles will show edge thickness more as well. That being said, depending on the actual strength of prescription, simply choosing a higher index of lens may be enough to get you into the frame you fell in love with.
Nylor Frames
Have you seen those semi rim, half rim, or floating frame glasses before? They are super cool and many people will prefer them over full rim frames for many different reasons. Just how does this lens stay in the frame without a full rim, you ask? Well it's very simple really! There is a little nylon cord that the lens sits in that is attached to the frame! The one catch is this: that lens needs to be strong enough and thick enough to drill a tiny little bevel around the entire edge of the lens for that cord to nestle in. This means that you should never ever use a 1.5 index lens in any kind of nylor 
frames because they are just not strong enough! The basic 1.5 lens is more likely to chip or break along that nylon cord, and many lens companies will not honor any warranty for this if the lens was done this way. You absolutely MUST have a 1.6 lens or higher (1.53 Trivex and 1.59 Polycarbonate is also useable, but we are only focusing on the average plastic lenses for the sake of this article) in order to be able to use any kind of Nylor mounted frame. Nylors can also be very sneaky! There is also a Metal Nylor style of frame available. This appears to be a full rim frame, but it actually isn't! Metal Nylor frames will have a full rim of metal that sits in the lens bevel instead of holding a lens in a frame bevel like the standard lenses would do. Metal Nylor frames are no different than other nylor frames, in which you just cannot use a 1.5 index lens, it just is not strong enough. It should also be mentioned, a metal nylor frame does not work very well for a higher prescription: in the high minus it will not hide the edge thickness at all, and for the high pluses the edges could be too thin to bevel, depending on the frame size.
Rimless frames
Many people just love the rimless glasses! These frames are generally made from Titanium, which is super duper strong, as we discussed last time in this blog series. The biggest reason people enjoy this style of frame is because they are the lightest weight frames you can get, and many people love
how they basically look like you aren't even wearing glasses, they just tend to blend right in! Rimless glasses are attached to the frame by a drill mount - which is essentially little holes that go through the lens, and then the temples and bridge are attached via these little holes and some clear plugs. So once again, this lens needs to be strong so that we wont have any chipping or cracking around the drill mount holes in the lenses. Just like Nylor frames, you will not be able to use the 1.5 index of basic lens thickness. Another thing to keep in mind is how long these drill mounts will last. The most successful rimless wearers are the full time wearers. You know, those people who put their glasses on as soon as they wake up and then they leave them on all day until bedtime! For anyone who tends to take their glasses off and on all day long, a rimless would not be the ideal choice for you, because the more you take the frames off and on, the more you open and close the frames, the more likelihood that the plugs holding the lens in the frame will loosen up over time and get pretty floppy and sloppy looking on your face! This can easily be fixed, but may take some time to do, as not all lab workers have the ability or the confidence to remount a rimless frame.
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Of course this doesn't cover every style of frame that is out there, but it certainly covers some of the most popular styles and the most common issues for people when choosing new glasses. It is certainly important, especially for those with stronger prescriptions, to consider not only what a frame looks like on their face, but also how the glasses will end up looking once the lenses are cut into it.
