For nearsighted people, the distant objects are blurry, while near objects appear clearly. The prescriptions for nearsighted people have negative values in the SPH field.
For farsighted people, the distant objects appear clearly, while near objects are blurry. The prescriptions for farsighted people have positive values in the SPH field.
Presbyopia is an age-related condition in which the lens of the eye becomes less flexible. So most people do not notice any significant problems until they are 40 to 50 years old. The prescriptions for presbyopia have positive values in the ADD field.
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