george wrote:I'm not an eye doctor, but I am pretty good at math. I'd say the difference is 0.02.
It's an interesting question and I'm guessing if I did a bit more searching around I could find more on the mathematical formulas behind lens thickness and lens material. The important factors I would think would be the lens thickness as well as the weight of the material. One interesting aspect of your question is that polycarbonate lenses are typically 1.59 index, yet Zenni has some sort of material they typically use with an index of 1.57.
Looking around, I did find this lens thickness calculator that you can try out. Your prescription seems to be in the medium range - mine is MUCH weaker, but many people have much stronger prescriptions. A stronger prescription will need a thicker lens (I'm not an eye doctor, but I'm pretty sure this is correct). The material of the lens determines how thin glasses can be in the center. A stronger material like polycarbonate can be cut thinner in the middle. The strength of the prescription combined with the refractive index (higher in high index lenses) determines how much thicker the lens needs to be at the edges. A larger lens will get even thicker at the edges.
The above referenced calculator will give you an estimate of the lens thickness at the edge. I just guessed at how to enter in your prescription and guessed at a pupillary distance and a frame eye size. I then selected the mid-range 1.56 index (which is close to the 1.57 of Zenni's lenses) and compared the numbers to the polycarbonate lens, which should be a 1.59 index. While I don't really know what I'm doing - it looked like the difference was about 0.2mm - which to me seems like it wouldn't be worthwhile.
Perhaps there is a real eye doctor out there that can weigh in on this one? I saw you posted a message on optiboards, but unfortunately, they don't allow non-professionals to post messages, as I'm sure you'd get an answer that you can be much more confident with from one of their users.
alpjeffrey26 wrote:There is not much difference between a 1.57 or 1.59 lens. Usually with my patients, if they're prescription is -3.50 or higher I put them in a 1.67 hi-index lens to help with the thickness. But that's just what I do. Others may feel differently. There is also the difference between the materials. 1.67 hi-index is the plastic lens which if you're used to wearing a polycarbonate lens you may notice a difference in the clarity of the lenses. I know that I've switched back and forth myself and I like my poly lenses better. But I'm just used to poly more than the 1.67. I also end up picking out plastic frames for myself so the outer edge thickness is hid pretty well with that style of frame. Hopefully this helped and I didn't ramble too much.
Blindman wrote:Is there a reason for this? Isn't the object for me to get as close to 20/20 as possible?
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