What is the difference between a 1.57 and 1.59 lens?

Getting the best value for your money when it comes to eyeglasses, sunglasses, eye exams, and contact lenses.

Postby Blindman » Sat Aug 28, 2010 2:00 am

My prescription is -4 and -3.50 diopters with a cylindrical of -.50 on each. I plan on buying a plastic frame from zenni. Should I even bother upgrading to a 1.59 lens or is 1.57 and 1.59 barely noticeable in thickness?
Blindman
 
Posts: 2
Joined: Sat Aug 28, 2010 1:43 am

Postby george » Mon Aug 30, 2010 10:53 pm

I'm not an eye doctor, but I am pretty good at math. I'd say the difference is 0.02. :D

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.
george
 
Posts: 179
Joined: Fri Apr 11, 2008 8:23 pm

Postby alpjeffrey26 » Tue Aug 31, 2010 2:02 pm

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.
alpjeffrey26
 

Postby Blindman » Wed Sep 01, 2010 1:23 am

george wrote:I'm not an eye doctor, but I am pretty good at math. I'd say the difference is 0.02. :D

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.


I tried out the calculator and it also gave me a .02 difference on the edge, which seems like nothing. I guess I'll with 1.57 for now. Thanks for the url and your reponse.

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.


It did, thank you. If you don't mind I have a couple of quick questions I'd like your opinion on. I went in for an eye exam not that long ago and I noticed that when the optometrist was telling me to read the eye chart I couldn't focus on the last and smallest line of numbers to tell what they were. I assumed the optometrist would keep switching to a stronger lens so I could focus in but after one or two tries they stopped. Is there a reason for this? Isn't the object for me to get as close to 20/20 as possible?
Blindman
 
Posts: 2
Joined: Sat Aug 28, 2010 1:43 am

Postby sam » Wed Jan 23, 2013 10:04 pm

Blindman wrote:Is there a reason for this? Isn't the object for me to get as close to 20/20 as possible?


some doctors will go as far as using the 20/15 line during their exams, which is smaller than 20/20. So if he/she can get you to read a few letters that small even though you can read all of them it's good that you can aleast read a couple. There is really no way to tell if this was the situation unless you ask the doctor who refracted you.


Last bumped by Anonymous on Wed Jan 23, 2013 10:04 pm.
sam
 




Return to Eye Care

Who is online

Users browsing this forum: No registered users and 5 guests