It is not possible for a lay person or the patient to know whether the blurred vision is caused by underlying disease or the need for a new spectacle correction. I am told that I don't need a complete eye exam to deal with blurred vision. Those who may advocate providing a refraction in isolation from a complete eye examination are overlooking the fact that the source of blurred vision is not always a refractive error. Certain drugs taken for the treatment of general health problems may also result in a transient change in refraction. Environmental and occupational factors, trauma to the eye, or dietary deficiencies may also contribute to refractive changes.
Proper diagnosis is necessary to determine the true cause.
Although objective means are available for measuring the refractive state of the eye, this information cannot automatically be translated into a prescription for eyeglasses or contact lenses. This information is needed to adequately prescribe glasses. Improper or inadequate eyeglass prescriptions based only on refractive information may alter eye coordination and focusing ability, create visual distortion, eyestrain, headaches, dizziness or double vision, and mask symptoms of eye disease. A refraction to determine a prescription for eyeglasses or contact lenses should not be performed independently of an eye health and vision examination.