The symptoms of myopia and spasm of accommodation are really similar. Nearsighted people have difficulty reading road signs and seeing distant objects clearly, but they can see close things, like read a book or use a computer.
Other symptoms include squinting, headaches and eye strain.
However, the two eye issues are quite different in character. Nearsightedness occurs when the eyeball is too long or curved relative to the focusing power of the cornea and lens of the eye. The light rays, therefore, don't focus correctly, and there appears a distorted image.
Most commonly, myopia is hereditary and starts in childhood. It may get better or stabilize in adulthood, but in some cases in aggravates even more as the individual hits adulthood.
Myopia typically begins in childhood and you may have a higher risk if your parents are nearsighted. In most cases, nearsightedness stabilizes in early adulthood but sometimes it continues to progress with age.
As for the spasm of accommodation, it is referred to as false myopia or pseudomyopia. Pseudomyopia refers to an intermittent and temporary shift in refraction of the eye towards myopia, in which the focusing of light in front of the retina is due to a transient spasm of the ciliary muscle causing an increase in the refractive power of the eye. This issue may appear because of visual overload, constant work in front of the computer, etc. Because false myopia is associated with a spasm, and not a permanent change in the eye structure, it can be completely removed with help of eye exercises.
Shortsightedness is often an accompanying condition with myopia, and it causes vision statistics to be worse. An individual with vision statistics of -6 may actually have true myopia as low as -2. This is why it is totally possible to improve vision by up to 4D through exercises.