base in prism some individuals will read better with lesser prism at some point the prism stops superimposition and confusing images finding the best prism power can be determined with known tests or simply with the text of interest to an individual finding a best prism power is seen by watching visual concentration during speaking showing uncharacteristic visual concentration and integration without averted gaze the perceived stabilization of visual space is helpful functionally for posturing breathing speech and communication movement and reading the most common prism powers of about 9 0 diopters may be used can be utilized in the final prescription usually the power is within the range of about 3 0 to about 9 0 diopters but in some cases more or less power may be used to facilitate reading and movement so that the range of power may be between 0 12 and 45 diopters as mentioned above the prisms for both eyes are usually oriented base inward toward the patient 39 s nose but one or both prisms may be more effective for a patient when oriented base outward the final lens prescription for an individual may typically be prepared by an optometrist or ophthalmologist for individuals with autism who are not yet of presbyopia age who require corrective lenses for reading or near vision reading powers such as in the range of 0.