LC_Tuning-Outside_the_Box

Sliding class-A hearing aid...

I can assure you, wearing a DSP-based hearing aid myself, that analog is far superior for intelligibility, but does eat more battery. ...Jim Thompson

I had progressive lenses in the mid '70's, but went R-K in the late '80's. Then lens implants after that. So I have two pairs of "Clic's", one pair at 22" for the monitor, and one pair at 14" for book reading.

I keep hoping that speert.com will soon offer a "Clic" that is bifocal. ...Jim Thompson

Hearing aids aren't exactly telephone equipment. Completely different product with completely different tradeoffs.

I have a pair of progressives set for about those distances. I keep a set of such Zenni's at work and one here at home. I have a couple of pairs of distance glasses, too (good thing since I just broke one lens).

Didn't wear any glasses until '07. There really isn't any point to corrective surgery for presbyopia because glasses will still be needed. I'll probably have cataract surgery in a couple of years, anyway.

Doesn't work for me. I have to take them off to read a book, and it's only slightly better than with the computer glasses.

I had progressive lenses in 2000, but the VA won't provide them, and I can't afford them out of pocket.

Wow. Glass? That's nasty.

I prefer glass--they don't scratch nearly as easily. IIRC the minimum USA thickness is 2mm, and 1,0mm in Europe, the result being that some people order glass lenses from Europe.

The math is easy. The units are 1/(focal length in meters) = diopters, and you add them, like conductances.

You print a starburst pattern with compass markings, like this:

\|/ --+-- /|\

put it beyond your focal length, then slide it toward your head along a ruler until any first line is clear, and note the distance. That gives you your first focal length and first angle.

If it's 33cm, your eyeball's focal length is 33cm or

-3 diopters. Rx = -3D.

If all the lines clear up simultaneously you're done (no astigmatism). Otherwise, continue bringing the pattern closer until the line perpendicular to your first measurement is clear.

If the 2nd measurement is 28cm, your focal length on that "axis" is

So, your focal lengths are 3.00 and 3.57 diopters in that eye. The lens to correct that can be specified as either -3D sphere with an additional -.57 cylindrical correction in the 2nd axis, or -3.57D sphere with 0.57D cylindrical along the first axis. They'll round that to 0.50D.

If it's your left eye, that's written O.S. -3.00 -0.50 x . It's a lot easier than it sounds. It takes me 30 seconds per eye. Definitely less trouble than ordering and trying multiple sets.

No. The line that's aligned with the axis you're measuring will come into *perfect* focus (assuming simple astigmatism, which is as good as they can correct anyhow).

The O.D.'s test is confounding. It conflates the errors of the two axis, and the test patterns don't let you clearly distinguish which axis is out of focus. The method I describe separates the two so they can be handled independently. (It's more robust, but it takes sophistication.)

Yes, but apparently not everywhere online.

I still like knowing in advance--I've had to gently correct them a couple times.

Cheers, James Arthur

Nope. Polycarbonate. Zeiss lenses, in fact.

I scratch a few pair of lenses every year. Optometrists guarantee them for a year. I've collected a few times. Zenni makes self-insurance less than a big deal, though.

Simple enough, unless it goes negative. ;-)

Makes perfect sense. Thanks!

I didn't think of the starburst. That clarifies everything.

They're supposed to but there is no way to enforce the issue. Zenni asks for the prescription and date.

I'll definitely give it a try. Thanks again!

even

So raise hell with the vendor. You have designed better analog hearing aid ICs haven't you?

?-)

Right! Hearing is a System. There are MORE nerves going FROM the brain to the ear than going from the ear TO the brain. Absolutely an incredibly complex system.

Not everyone is created equal! :)

Jamie