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 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.
The most common type of myopia, the mild form, has been reported in 25% of the adult population in the United States and in 25% to 35% of children who are school age. High degrees of myopia are called degenerative myopia or pathological myopia and occur in 1% to 9% of adults in different countries.
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.
With myopia, the eyeball is elongated and therefore the tissues within the eye, including the retina, are stretched and are thinner than normal. The stretching makes the retina prone to several disorders:
- If this stretching occurs at the back wall of the eye, it creates a particular type of macular degeneration called myopic macular degeneration, which can be treated with laser photocoagulation or photodynamic therapy. Myopic macular degeneration is usually less severe than age-related macular degeneration.