A SHORT HISTORY OF MYOPIA RESEARCH
Probably no aspect of vision has been the subject of as much discussion as the cause and prevention of myopia. High degrees of hyperopia and astigmatism have always been explained rather satisfactorily by attributing them to a congenital deformation of the eyeball. The rare cases of high myopia at birth fall into the same category. But acquired myopia, developing as it does in eyes which are normal at birth, has always been an enigma. Because the affliction is so widespread and has affected hundreds of millions of people, volumes of statistics have been assembled and much labor has been devoted to studying it.
The researcher who begins a study of the myopia literature accumulated over the years is soon struck with a feeling of confusion and hopelessness. It seems that every imaginable theory of the cause of myopia has been proposed by someone and evidence presented to support that theory. And for every researcher who has "proven" something, there is another researcher who has "disproven" it.
About the only thing they have been able to agree on is that children are generally free of myopia when they begin school, but that the incidence (frequency) and the severity of the myopia increase steadily through the school years.
The first person to distinguish between the conditions that we now call myopia and hyperopia is thought to be Aristotle (384-321 BC). The first use of the word myopia, however, is attributed to Galen (138-201 AD) who lived for many years in Rome. The first written record of the term is in Libris Pandectorum, a compilation of Roman Law that was completed in 65 AD. In Greek, myein means to close and opos means the eye. Thus, the original meaning of the Greek word myopos and the Latin word myops was to describe a condition in which an individual attempted to see clearly by partially closing the eyes. This squinting is frequently resorted to by myopes since it restricts the vision to a narrow band across the center of the pupil. This cuts off the light rays passing through the top and bottom of the lens (rays which would only increase the amount of blur at the retina) and thus improves the vision temporarily. In addition, if the narrowing of the eyelids can be used to put sufficient pressure on the front of the eye, the eye can temporarily be made shorter and less myopic.
As long ago as 1813, James Ware noted that the men under his command were rarely nearsighted, while the officers of the Queen's Guard were frequently nearsighted. He felt that the officers became nearsighted because they were all educated and were able to read. The men in his company, on the other hand, were not educated to the point of being able to read. It appeared to him that reading was the cause of the myopia.
Cohn (1864), in describing work that he and others had done, presented strong evidence that myopia developed in many youngsters only after they had begun attending school. His conclusion was that it was attending school and the accompanying overuse of the eyes for close work which produced myopia. Cohn is therefore considered to be the originator of the environmental theory of myopia development. He tried to point out the need for improved reading habits and illumination in the schools.
His results were repeated and confirmed by other investigators and led to efforts around the turn of the century to minimize the effects of reading, writing, and other close work in the schools. In Germany and elsewhere, rules were laid down regarding the size of type in schoolbooks, the distance at which the book was to be held, the minimum amount of lighting, etc. The results of these measures were for the most part disappointing. These efforts failed because they did not go far enough, although they were a step in the right direction. Also, since these efforts took place before electric lights came into widespread use, it seems unlikely that the lighting in the schools could have been very good.
For some reason, it appears that no real attempt was made to reduce accommodation by the use of reading glasses or bifocals, as will be described in a later chapter.
Tscherning (1883) examined 7,523 military recruits in Holland and recorded the percentage of myopia occurring in several classifications.
|Previous Occupation||% Myopic|
|Farmers and Fishermen||2.45|
|Handworkers (Coarse work)||5.24|
|Handworkers (Fine work)||11.66|
A similar relationship between the incidence of myopia and the amount of close work involved in the occupation has been found by many investigators since then.
Figure 1 shows the incidence of myopia among nearworkers and non-nearworkers as reported by six different researchers:1 The statistical evidence is conclusive that the incidence of myopia is positively related to the amount and intensity of the close work. In some countries, such as Japan and China, the incidence of myopia is very high. From the environmental point of view, it is easy to see an explanation for this in the large amount of intense close work that is necessary when the children in these countries learn to write with oriental characters. Much more painstaking effort goes into drawing oriental characters than into writing with alphabets, as in English.
In Singapore, the vision of 421,116 males between the ages of 15 and 25 was examined. In 1974-84, 26.3% were myopic; in 1987-91, 43.3% were myopic. Both the prevalence and severity of myopia were higher as the level of education increased. The prevalence rate was 15.4% in males with no formal education and increased steadily through the education levels to reach 65.1% among the university graduates in 1987-91. The authors state that their findings confirm indications from other sources that the association between the prevalence and severity of myopia and education attainment is real.2 More recent studies show that the incidence of myopia is still increasing.
For example, it was found in 1988 that the prevalence of myopia in the children in Taiwan was over 70%.3 And a study in 1996 of 345 National Taiwan University medical students found that the myopia prevalence increased from 92.8% to 95.8% over a five year period.4
If myopia is inherited, then why are so many myopes found in the "learned professions" and so few in occupations requiring little schooling? Why, in a play or film, does an actor wear glasses when playing the part of a highly educated person? In order to explain this, those who claim that myopia is inherited have had to develop what might be called the "gravitational" theory. They claim that since myopes have difficulty seeing in the distance, but no trouble seeing close, they tend to "gravitate" toward those occupations which involve close work. The error in this explanation should be obvious. There may have been some truth to this concept in the days before concave lenses were made available to correct myopia, but in modern times myopia does not force anyone to a lifetime of close work. Myopes (with their corrective lenses) now take part in most activities that require good distance vision.
Over the years an incredible amount of research, some valuable and some worthless, has been carried out on the cause of myopia. Many theoretical arguments have been presented and staunchly defended. The viewpoints have been argued back and forth, but we still have with us the genetic theory and the environmental theory, each with its proponents. This is also known as the nature versus nurture controversy.
Thorington (1900) and numerous researchers since then have noted that myopia is more common in people who were shy, who had few friends, and who preferred indoor activities. Many theories have been developed to explain this in addition to the obvious explanation that such people are more likely to lead a life involving much reading and other close work.
Hayden (1941) found that midshipmen at the U.S. Naval Academy, all of whom were nonmyopes when they entered, frequently developed myopia. Between the second and fourth years, twenty percent developed visual-acuity loss sufficient to disqualify them for naval service.
Similar problems with myopia have plagued the U.S. Military Academy at West Point. Since 1912, vision standards have been changed numerous times to reflect the problem of visual-acuity degradation among the cadets. New cadets are accepted at the academy with several diopters of myopia and more than half of each graduation class wear glasses or contact lenses to correct myopia. This increase in myopia is all the more significant because it is taking place not in rapidly growing children but in young adults who have essentially completed their growing years.
There is no point here in going deeply into everything that has been published under the general topic of myopia research. Much of it is by people who have set out to prove their own particular preconceptions. Much of it leaves the reader with the impression that the researcher is examining one small aspect of the development of myopia without having a clear understanding of what benefit, if any, can ever come from the research. In the meantime, millions of children continue to become nearsighted each year and little genuine concern is shown about it.