What
is myopia?
Myopia (nearsightedness) is the inability to focus on objects in the far distance,
but with the ability to see close objects well. This visual problem is a result
of an elongation of the eyeball (see figure 1) so that distant objects cannot
be focused on the retina by the lens of the eye.
Parallel rays of light entering the eye from the distance are brought to focus
in front of the retina, thus creating a blurred image. Spectacles and contact
lenses can correct this visual abnormality.
Figure 1. Cross section of a myopic eye.
How common is myopia?
The most common, mild type of myopia has been reported in 25% of the adult
population in the United States and in 25% to 35% of school children. High
degrees of myopia are called degenerative myopia or pathological myopia and
occur in 1% to 9% of adults in different countries.
What is the cause of myopia?
Genetic factors influence the development of myopia. However, the causes of
most cases of myopia are poorly understood. Only a few rare forms of myopia
have been reproduced experimentally.
How does myopia cause retinal disease?
Because the eyeball is elongated, the tissues within the eye, including the
retina, are stretched and are thinner than normal. The stretching makes the
retina prone to several disorders:
1) If this stretching occurs at the back wall
of the eye, it creates a special type of macular
degeneration. Sometimes this “Myopic
Macular Degeneration” can be treated with
Laser photocoagulation or Photodynamic
Therapy. Myopic macular degeneration is usually
less severe than Age Related Macular Degeneration.
2) If this stretching occurs at the equator of
the eye, it can cause a condition called Lattice
Degeneration. Lattice degeneration, in turn,
increases the risk of Retinal
Tears and Retinal Detachment. The incidence
of Retinal tears and detachments is higher in myopic
people than in non-myopic people. |
