ABO NOCE Practice Test

Which formula is used to find total decentration?

1. A + DBL - PD

2. PD - A + DBL

3. A + PD + DBL

4. (A + DBL) - PD

The correct answer is: (A + DBL) - PD

The formula used to find total decentration is derived from the relationship between the position of the optical centers of the lenses, the distance between the eyes (interpupillary distance or PD), and the lens parameters. In the case of total decentration, the goal is to determine how much the optical centers of the lenses should be offset to achieve proper alignment with the person's pupil centers. The total decentration is effectively the sum of any lateral displacement of the lens (represented by A and DBL) adjusted by the PD, which indicates the spacing of the eyes. The formula reflects this relationship by adding the values of A (often representing the distance from the midpoint of the lens to the optical center) and DBL (the distance between the set of lenses or their respective optical centers) and then subtracting the PD. This approach ensures that the resulting value accurately represents the total adjustment needed to properly position the optical centers in relation to the eyes, making it suitable for calculating total decentration accurately. Thus, when you assess these values and plug them into the formula, it allows for precisely determining how much decentration is necessary to achieve optimal visual performance.