Sharp eyes, sharp eye exam?

September 17, 2012 9:27 AM

Eyes 20/10 with correction, where to get the sharpest prescription in the US?

L C F T D ... CWA Local 7019

I am nearsighted but with no astigmatism, and have 20/10 vision with correction.

How do I get a prescription in the US that gets me the absolute maximum supervision?

That is, I've seen my prescriptions over time vary by I think 0.25, but never less than that. I'm assuming this is the limit of measurement ability at an optometrist's office. Is that so?

Would a more precise measurement make a noticeable difference with glasses? Do optometrists even have the equipment to measure more precisely? And can lensmakers work with more precise measurements than standard?

(Feel free to hit me with the sordid details of the world of optometry, lens equations, etc. I'm a geek)

posted by zippy to health & fitness (12 answers total)

I got contacts for the first time a few years back and was stunned by the world they revealed. I had super-vision as a kid and could make out the jacket color of a mountain climber miles away. With contacts, its very similar. All of these details that I'd never noticed with glasses jumped out (20/15 I think). It takes a few tries to get the right contacts though. The eye doc (there is a difference, BTW) used a retinal imager and automatic refractor for measurements, in addition to the regular "1 or 2?".

BTW - uncorrected we have another form of super-vision: microscopes. I use that more than long distance so I stuck with glasses. It's nice to have the option though.
posted by jwells at 9:46 AM on September 17, 2012

That is, I've seen my prescriptions over time vary by I think 0.25, but never less than that.

No, it's the limit of how accurate the correction is. I seem to remember my optometrist telling me contact lenses go in .25 increments while glasses go in 0.1 and are therefore more accurate, but it was a while ago so I may have got those around the wrong way. Basically, how great your correction is depends on how close you are to one of the set increments they can correct to. Astigmatism also makes it more complicated but you don't have that problem.

Personally I find contacts seem more clear even though mine are less accurate than my glasses, presumably due to lack of frames and having the correction right up by my eye (so I don't end up looking out the side when I turn my head). So factors like that can make a difference too.
posted by shelleycat at 10:04 AM on September 17, 2012

Oh, my "no" at the start above is in reference to the accuracy of measurement part of your question. They can measure a lot more accurately (or my super-awesome optometrist could anyway) but glasses and contact lenses come in set increments of correction.
posted by shelleycat at 10:05 AM on September 17, 2012

I asked a similar question once while getting an eye test at an optometry school at a major US university. Instead of the normal test, they actually dilated my pupils and I believe relaxed the muscles in my eyes (maybe it was the same thing). They then went through the normal testing procedure. Apparently this was to ensure I was not using the eye muscles to compensate for the variations. I don't think this prescription differed significantly for me compared to the standard methods...

One other variable, your optimum prescription might also change as a function of time of day and/or lighting - or probably other external perturbations as well.

When I got contacts we tried several brands and several variations around the measured prescription each for a couple days at a time. I got lucky with one brand and in the end a prescription not very close to my measured value (I have an astigmatism as well which complicates things somewhat) - the set I found just gave me the best possible vision of all the sets we tested...
posted by NoDef at 11:18 AM on September 17, 2012

Your eyes actually vary considerably over the course of the day. Measured extremely accurately, your prescription could be +/- 0.25 diopters just between morning and night on the same day. Given that, there's not much point to measuring too finely (until we develop glasses which can adapt fluidly, but by then we'll probably have better corrective surgery and... yeah).
posted by anaelith at 11:21 AM on September 17, 2012 [1 favorite]

The sharpest glasses I've gotten are from Zenni. You can pump up the refractive index to a higher level than what they give you at the mall. (I think I said that right)
posted by thylacine at 1:12 PM on September 17, 2012

If you will do contacts, gas permeable ones gave me sharpest vision. (I had astigmatism and myopia before I had LASIK.) The gas permeable ones are less comfortable, but miles better than soft contacts or glasses.
posted by artychoke at 1:22 PM on September 17, 2012

Lens material makes a difference in the optics. Regular plastic is better than high index (thinner). Polycarbonate is the most common lens material, but I believe has the worst optics. Glass is best, but I'm not sure anyone will give it to you, at least not in the U.S.
posted by still_wears_a_hat at 2:50 PM on September 17, 2012

I'm not sure if this is what you are asking, but there isn't a "more is better" thing going on with vision correction. Like focusing a camera, there is a right spot. And all the other spots are not going to be in focus.

The dioptre is the unit of measurement for eyeglass prescriptions, and a quarter of a dioptre is pretty tiny when you consider the size of the eyeball. It is within the "noise" of what your eyeball can accommodate.


The sharpest glasses I've gotten are from Zenni. You can pump up the refractive index to a higher level than what they give you at the mall. (I think I said that right)

The refractive index is not a measure of sharpness. It is a measure of how much the material bends light as it goes through the lens. It is sort of like a multiplier. (I am surely wrong on the math, but the general idea is this: if you need a -6 dioptre correction and you are using glass with a 1.5 index, the lens can be ground with a -4 curve to get to -6. But if you are using 2.0 material, you only need a -3 curve. Thus your lens can be thinner and lighter.) There are vision tradeoffs for each type of material. Some materials can go really thin, but they will give you the rainbows in your periphery effect. Or the fisheye effect.
posted by gjc at 6:57 PM on September 17, 2012 [1 favorite]

You might be interested in something like high-definition eyeglass lenses. (I have zero experience with them, so just mentioning as a possibility you might explore.)
posted by exphysicist345 at 7:25 PM on September 17, 2012

As fodder for future researchers of this topic, the closest external info I've found in the neighborhood of an answer is on optometry for 'sports vision,' with some optometrists specializing in vision correction for pro athletes.

The testing they perform is more thorough than the exams I've had, with additional task-relevant exams (they look for moving object detection and eye dominance, which I understand can reduce peripheral motion detection in the non-dominant eye, I believe.) They measure eye correction in increments of .125 diopters. They think they also test for which color of light provides the best visual acuity for the patient.

The fact that the article in the link is titled "Sports Vision Testing:
An Innovative Approach To Increase Revenues" is a billboard-sized red flag, but the two authors, Kirschen and Laby, have other, more academic publications on the subjects, and their PhD/OD/MDs from schools I've heard of, instead of Hollywood Upstairs Medical Academy.
posted by zippy at 9:47 AM on September 18, 2012

Exphysicist's link answers one of my questions: whether some lens labs can accomodate a more precise measurement of correction. From the link:

"With free-form lenses (also called digitally surfaced eyeglass lenses), the fabrication of the lenses from wearer's eyeglass prescription is optimized with advanced manufacturing tools ("surfacing" equipment) that are much more precise than conventional tools. In fact, digital, free-form technology can surface lenses in power intervals of 0.01 diopter (D), compared with 0.125 to 0.25 D increments of conventional eyeglass lens tooling."
posted by zippy at 9:53 AM on September 18, 2012