This clinic, doing various eye surgeries for visual disturbances, have come up with a nice promotional material. They sent many ophthalmologists (Possibly other people as well, but I’ll stick to what I know) this small folded page to show clients/customers. On the outside a text instructs to Open the page, hold it in front of you with a stretched arm (about 40cm), and check your visual acuity. If you open the page, the inside have an almost standard visual acuity test page, with lines of text in decreasing sizes, each line marked by the visual acuity level matching the ability to see it clearly.
So far so good. You can look what is the smallest line you see clearly, and check if it’s the standard vision, or if you have a problem. And hopefully (from their POV), if you have a problem you’d notice their company logo and consider contacting them for treatment instead of buying glasses.
As a nice touch, it’s been the Jewish New Year recently, so the lines consist not of random numbers but of a text telling you to have a happy and successful (and so on and so forth) new year. Not good for a proper professional examination, but cute for this crude check.
If you go to an optometrist, or a doctor, to have your vision checked, you’d notice that there are two different checks. One is for distance vision, where you’ll usually sit in a chair a few meters from the test patterns you’ll need to try and read. The second is near vision, where you’d be given some card to hold in your hand at reading distance (about 20cm officially). The near vision of course you’ll only get if you’re over 40 years old, unless there’s a specific medical reason to consider a problem earlier. The important thing here is that there are two different systems, measuring two different problems. Well, not entirely separate of course, you’re using the same optical system after all. But the optical problems that glasses or laser surgeries address are commonly the result of different problems.
When looking to the distance (Infinity officially, but a couple of meters are close enough) you don’t focus your eyes, that is the lenses in the eyes are relaxed and stretched. The common optical problems are caused when light passing through the lens doesn’t focus on the retina, but either in front of it (Myopia – Nearsightedness. More common) or after it (Hypermetropia). This tend to change with age, since as you grow your eyes grow, resulting in light focusing in a larger distance from the front of the retina. That’s why usually glass numbers tend to grow, you need more correction to offset the distance. At about 24 years old, the body stops growing, and you no longer need to change your glasses.
Near vision, or reading, problems start at about the age of 40. In order to look at close objects the muscles around the lens need to push it. The closer the object, the more force needs to be applied in order to allow you to focus. With age the tissue of the lens becomes less flexible and it becomes harder to apply enough force. Then you need reading glasses to provide some of the optical correction. And unlike distance, using reading glasses increases the pace in which the problem grows, since the muscles become less exercised and weaken faster.
There are of course more problems, some also corrected by glasses, contact lenses, or these surgeries, but that’s not the issue here, so I won’t go into them.
Why the long explanations? To emphasize the point that checking near vision and checking distance vision are two different things.
And 40cm has a lot to do with near vision. Not entirely, that’s true, but enough. What you see from 40cm is not very relevant to your visual acuity for distance.
I tried to check myself with their test page. It was very interesting to see I get to 20/15. That’s wonderful! I didn’t see that well for more than 10 years… What an amazing improvement. Nowadays I’m actually more at the 20/20 or 20/30 range. Which is also good, but is normal good, not above normal good like 20/15 would be.
Which brings us to another alight problem with this test page, beside it being irrelevant and showing a clear lack of understanding about how visual acuity is checked (And I’m supposed to let these guys operate on my eyes after that?!). They had the Ft. scale and the 20/x scale. Would have been very nice for most Americans for example, that probably heard someplace you want to see 20/20. But around here the used system is 6/x mostly. Conversion is extremely trivial, but still it’s hard to believe someone around here would have come up with it. Which means they probably stole the idea from some American clinic doing the same thing…
These Y/X scales, if anyone wonders, are not at all complicated. The numbers say that what you see from Y meters an average person would see from X meters. So 20/20 means that you see from 20 meters what an average person would see from 20 meters. 20/40 would mean that what you see from 20 meters, an average person could see just as well from 40 meters. What matters is the ratio, so 20/20 is 6/6 is 5/5, and 20/40 is 6/12 is 5/10.
And these averages were measured a long while ago, and not extremely accurately. And they’re only averages, so seeing 6/7.5 (20/25) is perfectly fine and not reason to go buy glasses (or do some other things like this clinic sells).
Though IMNSHO the law here is a bit extreme, allowing people to drive if they see 6/12 in one eye. Putting a person with one blind eye (so having no stereoscopic vision, depth perception, at all), and another eye that needs to get to half the distance a normal person would in order to see a problem on the road, behind the wheel of a car, strikes me as not particularly safe. But maybe it’s just me, other people probably don’t need to see anything in order to drive safely.
Anyway, to get back on track, these people are using a scale which is rarely used in this country, and employ a meaningless method to do the check. And all that in a promotional material which is meant to attract customers who will pay them a lot of money to perform precise medical procedures on them.
I can’t see that happening.
