Trying to work off my mild astigmatism, and wondering if there’s a place online I can order from that will let me put in say 0.35 CYL instead of having to choose between 0.25 and 0.5. Is that a “thing” anywhere in the world, or are quarter-diopters the smallest units anyone uses?
I’ve read that you can get lenses cut at 0.125D SPH steps rather than 0.25D SPH, but they are custom rather than mass-produced, which means they are expensive and probably not something you can just order anywhere.
I would imagine that whoever is making them could also make them with cylinder at the same steps, but I don’t know if they do.
I cannot make any recommendations since I don’t have any first-hand experience with them and I don’t recall where I saw this mentioned.
That said, 0.25D is the standard since the impact of a 0.12D difference in lens power is small enough that most people probably wouldn’t notice the difference except in specific circumstances. This is one of the reasons why astigmatism below 0.75D (and particularly below 0.50D) is hard to measure or even confirm––at that power, the difference can be too small to recognize. So, IMO, even if you can find a company that will cut lenses at 0.125D steps, it probably isn’t worth the extra time and money to do so.
Thanks for the answer. I was thinking that these days the lenses are probably made by some kind of computer controlled lens cutter and that it might just accept whatever value the operator types in.
I can believe that 1/8th diopter changes are hard to diagnose or measure, especially because the optometrist is dealing with people with bad / tired eyes who are sitting there looking through a bunch of different lenses, but for our purposes I think they’d be great. As you get down to low astigmatism values, there’s a big difference between “perfect” and “almost perfect”. I think 0.5 to 0.25 is a “big jump” vs 3.75 to 3.5.
If anyone seeing this knows of a place that does high-quality-custom-cylinder lenses for cheap bastards like me, please let me know!
No, basic lenses are made in factories (often in China) and produced in quantity. It is probably not cost-effective to make lenses in-house, particularly when they can pay less than a dollar per lens to buy them from Essilor (or whomever). I imagine that the equipment to make them probably requires high heat, a lot of ventilation (since you’re melting large amounts of plastic and resin), and takes up a ton of space. So making them in small batches would cost far more than just buying them.
Once the lenses arrive at the optician, they can be ground and cut to match the specifications of the frames and client. That process must be done on a much smaller scale, so the equipment is commodity priced and available in most optical labs.