A recent 2009 study found little evidence in support of vision exercises that supposedly slow or reduce myopia, ease dyslexia and correct conditions caused by physiological problems, like blurred vision. Eye exercises are useful for some problems, such as treating convergence insufficiency in which the eyes have trouble working together. They do not, however, seem to relieve myopia or dyslexia.
Source: O'Connor, Anahad. The Claim: Eye Exercises Can Enhance Your Vision. The New York Times, Health, 25 May 2009.