A patient is prescribed a +12.00D sphere with a fitting distance of 13mm. When the eyewear is dispensed at a wearing distance of 8mm, how will the lenses feel to the customer?

When a patient is prescribed a +12.00D sphere lens and the fitting distance is set at 13mm, the optical power is designed for that specific fitting distance. If, however, the eyewear is dispensed at a reduced wearing distance of 8mm, the effective power of the lens increases.

This is due to the fact that as the distance between the lens and the eye decreases, the plus lens's optical power is amplified. In this case, the prescription which was intended to provide the correct vision at 13mm will now make the patient see as if they are looking through a stronger (+) lens while at 8mm. Therefore, when the patient tries on the glasses, they will perceive the lenses to be stronger than what was intended, which can lead to discomfort or difficulty focusing.

Understanding the relationship between fitting distance and effective power helps in the dispensation of corrective lenses, allowing practitioners to anticipate and address any potential issues that might arise from incorrect fitting distances.