About myopia
Near-sight or myopia is
one of the most common vision problem and will touch the lives of almost half
the population at one point or another. Initially you can see things around
you quite clearly. It’s only things at a distance that are blurred.
Usually it starts during the school years when you begin to realize that you
have trouble seeing what is written on the board. Initially it is something
you can cope with but soon it becomes more of a problem and your eyes are
tested and fitted with glasses. However, as you begin to wear glasses the
myopia tend to progress and get worse and you need to have stronger correction
in order to see comfortably. Soon you are wearing the glasses all the time
What
The theories abound about
what causes myopia. The loss of distance vision has been known since ancient
time. The Greek concept of myopia was that too little spirit of vision poured
out from the brain and hence was too feeble to extend to a distant object.
However, not much attention was paid to vision problems until mid 19th century.
Interestingly enough during the first half to the 19th century the use of
glasses were discouraged. They were thought to aggravate the existing problem
During the 1860’s
German ophthalmologist Herman Cohn had observed that myopia increased as children
progressed through school. In 1866 Dr. Chon published his study of the eyes
of 10,000 children attending the schools of Breslau. He arrived at what seemed
a reasonable conclusion: namely, that use (and particularly abuse) of the
eyes was what caused myopia. Cohn’s theory dominated for the next 50
Dutch ophthalmologist
Donders thought that myopia occurred as a result of prolonged tension of the
eyes during close work and elongation of the eyeball. In “On the Anomalies
of Accommodation and Refraction of the Eye” (1864) Donders writes: “How then
is this prolongation explained? Three factors may here come under consideration:
1 Pressure of the muscles on the eyeball in strong convergence of the visual
axes; 2. Increased pressure of the pressure of the fluids, resulting from
the accommodation of blood in the yes in the stopping position; 3 Congestive
processes in the fondus oculi, which, leading to softening, even in the normal,
but still more under the increased pressure of the fluids of the eye, give
rise to extension of the membranes. That increased pressure and the extension
occurs principally at the posterior pole, is explained by the want of support
from the muscles of the eye at that part..” (pp 343) Until equipment became
available to accurately measure the size of eyeballs in vivo it was believed
that the cilliary muscle weakened and could no longer focus the lens. This
theory is still offered as the explanation by many eye-care professionals.
Ultrasound scans have objectively shown that with high degree of myopia there
is an elongation of the eyeball. What causes that elongation is a matter of
opinion. Some researchers thought that the problem was with increased pressure
in the eye. Kelly et al. (1975) refer to myopia as “Juvenile expansive
glaucoma.” However the pressure theory is unlikely since both coughing
and an increase in body temperature causes an increase in the intraocular
pressure.
