Avoiding the coke bottle look: do I need high index lenses?

October 1, 2015 4:40 PM

Ordering new glasses. Should I spring for high index 1.67 lenses over polycarbonate?

I'm finally replacing my old and broken pair of glasses. These will primarily be a backup to contacts but I will wear them around 1/4 of the time, so I'd like them to look good.

My prescription is -4 in both eyes.

In my initial order through Warby Parker, I ordered their standard polycarbonate lenses. They emailed me saying my prescription is high enough that I should go with 1.67 lenses for $30 more.

My current pair is 1.57 which was fine, although if they'd be noticeably thinner at 1.67 I might go for it. I'm not sure how 1.57 index compares to polycarbonate. I just don't want to pay for an upgrade that doesn't actually make any real difference in the function or look of the glasses.

Anyone faced this dilemma and have sage advice?

posted by geegollygosh to Grab Bag (13 answers total)

I'm deep on the + side- the biggest difference I noticed with the somewhat higher index lenses I got was a lot of chromatic aberrations. The lenses were thinner, sure, but not thin.
posted by wotsac at 4:46 PM on October 1, 2015

I think if you got more chromatic aberration, you must have ordered polycarbonate, actually. I was coming in here to say how much the chromatic aberration annoys me -- polycarbonate has the most among common lens materials.
posted by mister pointy at 4:51 PM on October 1, 2015 [1 favorite]

How much it matters depends on the shape and size of your glasses (and your interpupillary distance, since what really matters is how far from the center of the lens the glasses go). Plugging in some typical numbers in this lens thickness calculator I get that the thickest part of your lens lens might be 4.6mm with a 1.67 index of refraction and 5mm with polycarbonate. So it looks you should expect maybe a 8%-10% difference in maximum thickness.
posted by aubilenon at 4:52 PM on October 1, 2015 [1 favorite]

My prescription is -3.75 in both eyes. My 1.57 index lenses don't look at all coke bottle-y and I even have pretty large, roundish, frames. I wouldn't (and didn't) bother. I get compliments on my glasses frequently, in fact.
posted by bobobox at 4:58 PM on October 1, 2015

I love love love mine. -5.5 though, so I might be getting more bang for my buck!
posted by susiswimmer at 5:07 PM on October 1, 2015

The difference is a matter of a few tenths of a millimetre at the edge of your lenses. It really won't be noticeable unless you have incredibly large lenses. In fact, the width of your lens makes far more difference to the edge thickness than the refractive index does - try playing with some numbers in the calculator aubilenon posted above.
posted by ssg at 5:41 PM on October 1, 2015

Think about how long you wear glasses. Are you getting new pairs every few months? If not, amortize that $30 over years and you'll have your answer. Even if it's a 10% difference, I'd do it. It really depends most on how large the frames and lenses are. Larger frames/lenses are far more forgiving.
posted by quince at 5:46 PM on October 1, 2015

In my experience, this depends to a surprising degree on the skill of the lensmaker. I sprung for the high-index material and ended up with constant chromatic aberrations. The optician said there was nothing wrong with the glasses, so I assumed the material was a waste of money. When I got a new prescription, I went to a new place and explained my problems. They checked out the old glasses and found that the focal point was in the wrong place and the lenses were badly centered. My new glasses are high index and are great, definitely better than the polycarbonate I've used.

This is an interesting article on the subject from an optician POV.
posted by thetortoise at 5:50 PM on October 1, 2015 [1 favorite]

At a -4 I'm not sure you'll see a huge benefit of high over mid index, but you should get the best multi-AR coating available.

No anecdata about Warby personally, but I can second thetortoise that a skilled lensmaker and coating are critical. Perhaps consider ordering your frames without lenses and having the lenses made at an independent optician?
posted by a halcyon day at 5:56 PM on October 1, 2015 [3 favorites]

I'm at -7.5 and quite reasonably refuse to buy anything except 1.67 high index (to minimize chromic aberration, I also buy the narrowest frame that looks good, which is unfortunate because my face looks best in wide frames). I made the switch a long time ago though, and -4 is right about the tipping point.

A 10% difference would absolutely be worth $30 to me. And don't be afraid to get a second opinion on the prescription being made correctly if they don't feel right. You might feel a little dizzy from everything being crystal clear if your script has changed, but unless you're switching to progressive the transition should be very easy.
posted by serelliya at 6:02 PM on October 1, 2015 [1 favorite]

+ 1 for serelliya's comment about buying a narrow frame.

Another benefit of high-index lenses is that your view will be slightly sharper because you're looking through a smaller amount of material than polycarbonates.
posted by dlwr300 at 8:15 AM on October 2, 2015

Actually, the higher index lenses have more chromatic aberration than lower index lenses, i.e. higher index lenses are less sharp than lower index lenses. Howver, this would very likely not be noticeable in this case.
posted by ssg at 10:06 AM on October 2, 2015

Yes. Better vision, more comfortable, looks better in the frame, and better for the skin on your nose (less indenting).
posted by radioamy at 8:36 PM on October 3, 2015