Is it necessary to add power to determine vertical imbalance?

Vertical imbalance refers to the difference in vertical prismatic effect that may occur between the two lenses of a pair of glasses, especially in cases where there are different lens powers for each eye. This imbalance can lead to discomfort or visual disturbances for the wearer.

In general, it is not necessary to add power to determine vertical imbalance because it can be assessed through the existing prescriptions and how they interact with the optical center of the lenses. Vertical imbalance can arise simply from differences in lens characteristics, such as design and thickness, rather than solely from the added power. The prismatic effect is calculated based on the position of the optical center and the prescription of each eye, which does not require modification of the existing power.

When assessing for vertical imbalance, the key consideration is measuring the resultant prismatic effect based on the current lenses rather than altering them with additional power. Thus, understanding the way existing prescriptions interact allows the optician to determine whether vertical imbalance may be a concern without any adjustments.