True statement about vertical imbalance calculations: this calculation requires information from:

• A. 2 eyes
• B. 1 eye
• C. 3 eyes
• D. Cannot be calculated

Answer: (A)

Vertical imbalance is determined by comparing how the two eyes deviate vertically relative to each other. To quantify this, you need the vertical deviation measurements for both eyes. If you only have data from one eye, you can’t know how the other eye aligns, so the imbalance cannot be calculated. For example, if the right eye shows a 3 prism diopter hyperdeviation and the left eye shows a 1 prism diopter hyperdeviation, the vertical imbalance is 2 prism diopters. This illustrates why information from both eyes is essential.