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They don't know they give you
the wrong

A lot of persons wear bad eyeglasses without being aware of it.

Opticians and ophthalmologists do follow the procedure they learned: measure the short-sightedness of each eye then prescribe for each eye exactly the glass that will compensate that eye's short-sightedness.

That way, for twenty years, since the age of ten, I've been wearing glasses with a slightly different strengths. Last few years I've been wearing -5.75 on the left eye and -5.50 on the right eye.

Same strength for each eye

A few months ago I began wearing contact lenses. They're great. But it has been very difficult for my optician to find the right strength. Of course I got lenses with different strength for each eye. First trial the lenses were too strong. Next they were far too weak. Third trial they were good. Yet there was something "imperfect" with my right eye. I realized the lens on that eye was a little too weak. Knowing the lenses for my left eye were just the strength above I put on the right eye a lens initially meant for the left eye. The result was amazing. I'd never thought I could see things with such a perfection. I discovered Nature again. Not only can I see things perfectly, I can really feel being amongst those things (indoor performances are less significant because my eyes get dry, and only one lens washing product gives perfect results).

Most striking was when I began working with my computer while wearing those contact lenses. Normally I just work a quarter of an hour or an hour, then I must leave the screen. I always thought that was due to some laziness of my eyes or of my brain. Yet this time I stayed several hours in front of my screen with no particular tiredness. I got the same results with books. Immediately I thought that was not due to the contact lenses yet to the fact I was wearing lenses with the same strength on each eye. So I took a lens of -0.25 dioptre I own and taped it on my right spectacle lens. That way with my sptectacles too I was wearing the same lens strength for each eye. Again, I could stay hours in front of my screen without tiring out.

I told a friend about it, his reaction was very simple: "Well indeed, when I go to the optician I insist to have glasses with the same strength for each eye. I got aware of that fact several years ago."

A few days ago I've been told about a Dutch ophthalmologist who insisted on prescribing a friend's brother glasses with the same strength.

I don't know if what really matters is that both glasses be the same. But for sure the way most ophthalmologists and opticians calculate the strength of glasses is wrong for at least a part of their clients.

My friend and I found two possible explanations:

Wearing the same lenses although my eyes are different makes my left eye doesn't see perfectly when I'm looking at distant objects. Yet when both eyes work together the normal way I'm totally unaware of that fact. I can only notice it by closing my right eye. The global image I get when both eyes are working is perfect and more pleasant than with glasses with different strength.

Apart from seeing things better and be able to stay a long while reading a book or watching a computer screen, I immediately improved my best score at the mining game. I played several seconds faster first time.

So I went to my optician and asked him to change my spectacle's left glass.

(In fact I bought new spectacles. The ones I was wearing were totally wrong. The center of the glasses was a few millimeters towards the outside, downwards, and the surface was not perfectly perpendicular to the eye's direction of sight. By correcting these things I improved my eyesight too.)

The strength of the glasses should depend on the type of spectacles

I didn't have a problem with that. It's just a Mathematic result I computed out. If you ever used an optical system like a camera or a projection system, you know the sharpness of the image depends on the distance you put the main lens. The same is true for spectacles. Actually for weak dioptres it almost doesn't matter. If you have say -0.5 or +0.5, it doesn't matter whether the glasses are close to the eyes or further away. But when you have strong dioptres, for example -5.0 or +5.0, then the position of the glasses in front of the eyes matters quite a lot. For example when I want to see a little sharper something that's far away, I simply push slightly on my spectacles, to get them 2 millimeters closer to the eyes. Reciprocally if I pull my spectacles a few millimeters away from my eyes I become unable to read even big texts at a few meters distance.

The problem is depending on the type of spectacles you choose, the glasses may land at quite different distances from your eyes. That's easily a difference of 5 millimeters. Far example spectacles with big glasses usually put the glasses further away from the eyes than spectacles with little glasses. For strong dioptres that makes a difference of easily 0.5 dioptre. So why compute out a person's dioptres with a precision of 0.25 when the spectacles may cause an error of 0.5 dioptre? Such a difference can cause quite annoying problems.

My feeling is for strong dioptres, sort of a standard dioptre should be measured out for each eye. Then the strength of the glasses should be computed according to the way the spectacles adapt on the person's head, that is the distance they create between the eyes and the glasses.

(By the way, for strong glasses, little spectacles are way better to my feeling. The glasses will be ways lighter and there will be less light reflections. Especially the size of the images seen will be less reduced or increased.)

Eric Brasseur  -  October 14 1998  till  August 8 2004