Fig. 1: points of focus as a function of accommodation
I know little to nothing about the inner workings of the eye and therefore must write in very abstract terms. The premise under which I am laboring is as follows:
Nearsightedness is the result of the eye's focusing muscles becoming stiff after being held tense for long periods of time during close work.
The natural method of focusing, or accommodating, the eyes is through a series of muscles that become more tense as the eyes focus closer and closer. The point at which the eyes focus when no focusing effort is being made (e.g. when one is looking into the distance with no glasses on) is known as the far point. For a normal eye, the far point is infinity; for a nearsighted eye, it is some finite distance. Looking at anything at or beyond the far point requires no accommodation.
Accommodation is measured in diopters, which are used here as follows. Let F be the distance of focus, in meters, and let D be the accommodation in diopters. Then
F = 1/D => D = 1/F.
Fig. 1: points of focus as a function of accommodation
The power of lenses (i.e. glasses, contacts) is also measured in diopters. Technically, this gives the focal length of the lens, but the numbers' use in accommodation is as follows. If one is looking through a lens of strength G diopters,
F = 1/(D+G) => D = 1/F - G.
As is shown, the purpose of lenses is to change the scale of accommodation by some constant amount.
Minus lenses (i.e. distance glasses) have a negative power in diopters and will increase the amount of accommodation needed for a given point of focus.
Example: Looking at a point one-half meter away will take 1/(1/2) = 2 diopters of accommodation without a lens, but if one is looking through a -1.0 diopter lens, it will take 1/(1/2) - (-1.0) = 3 diopters.
Plus lenses (i.e. reading glasses) have a positive power in diopters and the opposite effect: they move the far point in, decreasing the amount of accommodation needed for a given point of focus.
Example: For the point one-half meter away, if one is looking through a +1.5 diopter lens, it will take 1/(1/2) - 1.5 = 0.5 diopters of accommodation.
Visual acuity is a "subjective" way to determine what strength of lens a person needs. A visual acuity reading consists of a pair of numbers: one is the distance at which the tested eye could read a certain size of letter (usually 20 feet, the test distance) and the other is the distance at which an average eye with a far point of infinity could read the same size letter.
Example: If an eye has a visual acuity of 20/200, it must be at 20 feet to read text that would be readable by the normal eye at 200 feet.
Maximum visual acuity for an eye is the acuity of that eye when looking through whatever lens is necessary to place the far point at the test distance. Unless an eye is damaged or diseased, maximum visual acuity generally ranges from 20/10 to 20/20.
Nearsightedness, according to the premise, occurs when the focusing muscles have become too stiff to move below some level of accommodation and the far point has moved in accordingly. Compare to the stiffness of body muscles after exercise.
Minus lenses will move the far point of nearsighted eyes out to infinity while the focusing muscles are still stiff. However, since lenses change the scale of accommodation, using minus lenses for any amount of focusing inside infinity will make the stiff muscles still stiffer and increase the degree of nearsightedness, requiring stronger minus lenses to correct it, ad infinitum.
Instead of moving the far point out with minus lenses, one may also relax the stiff focusing muscles by focusing beyond the far point nearly all the time, which will eventually move the far point closer to infinity, reducing and/or eliminating the nearsightedness.
Plus-lens vision therapy refers to the use of plus lenses to bring in the far point, thereby allowing reading while performing this relaxation.
Like many others of my discipline, as a child I took little interest in athletic and outdoor activities, relishing instead the world of books and computers. Until the summer of 2004, however, I enjoyed good vision, retaining my maximum visual acuity of 20/13 in either eye. I attribute the onset of my nearsightedness to an increase in the amount of paper homework set me in the spring of 2004.
I first noticed vision difficulty when I was attending a class where instead of writing on the board, the professor wrote on a notepad projected on television screens, for the benefit of distance learning students. I was barely able to read the screen.
I ignored it until after the class was over; then I noticed other difficulties and went for an eye exam, at which my visual acuity was measured at 20/40 in both eyes. I left the exam with a prescription for glasses, -1.0 diopters for either eye, and the advice, "Don't wear them when you don't need them; you'll give yourself eyestrain."
My first minutes as a confirmed visual cripple were spent in a mockery of something more extreme than my newfound nearsightedness: I had to navigate the bright summer day with my pupils fully dilated. I went around with my eyes closed, using my walking implement in the capacity of a white cane.
Upon getting home, I printed a Snellen eye chart to hang on my wall. With it, I confirmed the visual acuity measurements of 20/40 in either eye. While printing the chart, I had noticed something else: the optometrist's drops had left me temporarily unable to accommodate. This was actually lucky; instead of spending the afternoon using the computer, I watched a movie. The screen, some eight feet away, was beyond my far point. When the movie finished, I went to the eye chart to check my vision again.
My visual acuity had, in those two hours, improved to 20/30.
I passed it off at the time as some side effect of the drops, but it started the machinery of doubt rolling.
I had no doubt as to the way in which my eyes would be corrected. I was a student in a scientific discipline, unbothered by cosmetic scruples and athletic concerns; I also did not feel like placing pieces of plastic beneath my eyelids, or having other people insert laser beams and knives into my eyeballs. The next day I was out comparison-shopping for a pair of glasses. I went to several optical shops in my search. The optometrists at those shops, learning that it was my first pair of glasses, had some advice. One of them said, "Once you get used to the glasses, you'll be able to wear them even when you're reading."
That from a shop that was supposed to be holistically oriented, contradicting the optometrist at the large non-holistic clinic? Strange.
I felt rather hopeless about my new handicap. I had before had little interest in the science of eyes and lenses, but in the week while I was waiting for my glasses to be ground, I very rapidly gave myself an education on the matter. While I was about this business, scrolling through search engine results on nearsightedness, I came upon websites mentioning alternatives to minus lenses. Most of it was the typical mystic garbage peddled by alternative gurus and people trying to sell things. Plus-lens vision therapy was the only thing I found that made any sense. There were some engineers involved with it, and I knew: if an engineer is involved in anything, take a close look before disregarding it. Their advice: go get reading glasses and use them for reading.
I picked up my distance glasses from the optical shop; then I went to a drugstore and bought some +2.0 diopter reading glasses, over the counter. The +2.0 glasses would bring my far point in from one meter to one-third meter, reading distance.
When I got home, I checked my visual acuity on my Snellen chart: 20/40. The first time I settled down for close work with my reading glasses, I got a headache. I took this to be my stiff focusing muscles relaxing, which it was: after an hour and a half, my visual acuity had jumped to 20/25.
For some weeks I continued wearing the reading glasses when I was reading; when I entered my classes I also wore them for note-taking. My visual acuity remained between 20/25 and 20/30. I was puzzled about this until I worked out two things: firstly, that my far point had now moved out a good deal and with the +2.0 glasses at one-third meter I was still accommodating a diopter; and secondly, that I generally focused on more near objects even when I was not reading. I bought a pair of +1.25 diopter glasses, stacking them with the +2.0's to make +3.25 for close reading, and wearing the +1.25's nearly all the time. With the +1.25's on my visual acuity was 20/50, which was good enough for getting around.
My visual acuity abruptly jumped to 20/20 and stayed there.
Presently (December 2004) I still wear the +1.25's most of the time, stacking on the +2.0's for close work. The vision problems that drove me to get my first eye exam have largely disappeared; I am now taking another class in the same room with the distance-learning televisions, and I no longer have any trouble reading the screen without glasses. My visual acuity remains between 20/20 and 20/15 in either eye on my Snellen chart. For all practical purposes, I am no longer nearsighted.
Update, February 2005: I went to the optometrist for a new presciption and found that I have improved 0.75 diopters in either eye; my new prescription is -0.25 in both eyes. Here are both prescriptions (irrelevant personal information blanked out):
Fig. 2A: Prescription before vision therapy, -1.0 diopter
Fig. 2B: Presciption after vision therapy, -0.25 diopter
What I am discussing here is based only upon commonly-known facts about lenses and my own experience. My case was fairly uncomplicated: only one diopter of nearsightedness, the same in both eyes, and no eye diseases.
The point: See an eye doctor before trying this, to confirm that nearsightedness is indeed your problem.
The first thing to do is to determine the degree of nearsightedness - where your focusing muscles are stuck. This is best done by having an eye exam and getting a prescription for distance glasses, or knowing the strength of a current pair that still give maximum visual acuity.
Once you have calculated the degree of nearsightedness, select plus lenses (reading glasses) to move your far point in (or out) to the point at which you will be doing your close work. Let G be the degree of nearsightedness, F be the desired far point, and P be the required strength of reading lens. Then:
P = 1/F - G.
If P is negative, or if it is different for both eyes and you want to work on both at once (i.e. not patch over the better eye while reading until both eyes are equal), an eye doctor will have to prescribe the glasses. Otherwise, reading glasses of varying strengths are available without a prescription in drugstores and optical shops.
Once you have the glasses and are ready for close work, you will want to keep the object (book, computer monitor, etc.) as far away as is practically possible. When an object is moved beyond the far point, it will start to blur; the blur increases with greater distance beyond the far point. Rule of thumb: if the object is not at all blurred, you are holding it too close. I read at such a point that the text is barely legible, when I can.
In addition to wearing the reading glasses for close work, you should also stop wearing distance glasses (or wear a less powerful pair if removal is practically impossible).
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