Now before we start talking about the lens materials that are available to use for your patients. it's important that we understand the different terminology in talking about those materials. So, let's talk about abbe value, specific gravity, and index of refraction otherwise known as refractive index.
Now Abbe value simply describes how clear a lens is. So, the higher the Abbe value of a certain material, the clearer the patient is going to perceive their vision through that material. Specific gravity is just simply how heavy is it. So, the higher specific gravity the heavier that material is meaning the heavier the lenses will be on your patient's face. Finally, the index of refraction or refractive index speaks to actually how thick the material is. So, the higher the index of refraction the thinner your lens is which is why high index materials are thinner.
Now, let's get into the different materials out there. First, we have CR-39. CR-39 is the base stock material that all lenses come in. When you order them from your lab, CR-39 actually stands for Columbia Resin 39th. It's the 39 formulation of that material. And this is the base option, which if you look at our chart that we’ve attached, that's actually the clearest material next to glass which is the most obvious choice when we're talking about High Abbe value but it's also the heaviest and not as impact-resistant as these other plastic materials. So, CR-39 is the base material that everything comes in.
Next and probably the most popularly known option is polycarbonate. Now polycarbonate was the standard for a long time. It’s impact resistant which means it's really really safe. The index of refraction isn't too bad, but also, it's very light. It has a very good specific gravity. What it actually lacks in is Abbe Value. Abbe Value of a plain polycarbonate lens isn't that great, so somebody that is used to glasses made of actual glass or CR-39 that you put into polycarbonate just aren't going to feel like they see as clear through it.
Next we have Trivex. Trivex is also known as Phoenix in certain labs. And trivex was actually designed specifically for those drill mount frames, the rimless frames. It’s light right so the specific gravity is pretty good on this. The Abbe Value is actually clearer than polycarbonate and it has the added benefit that when we drill holes into it, it doesn't crack like Polycarbonate would. So, it is actually a stronger material and even when you put anti-glare on it and compare that to something like polycarbonate the impact resistance is identical.
Next we have high index. Now a high index you’ll see with a lot of numbers after it. High index materials go anywhere from 1.53 all the way up to 1.74 and what that number actually refers to is the index of refraction or refractive index of that lens. So, the higher that number, the thinner the lens is, now what you need to understand is while that lens material is made up of a lot of different materials, the higher index actually has a little bit worse Abbe Value. So, your patient is going to get something that's thinner and lighter, but maybe not as clear. And it's really to understand the difference in those when you're talking your patient to not go too high just to try and give them thinnest, because our ultimate goal here should be to give somebody of the best quality of life, which is creating a balance between how clear do I see and how comfortable do I have that vision with. Because if I'm not comfortable in my glasses, I'm not going to wear them which means I’m not going to see clearly.