ABO NOCE Practice Test

Which formula is required to calculate prism power?

1. Power = Prism / decentration

2. Power = decentration / Prism

3. Prism = lens power x decentration

4. Prism = Power + decentration

The correct answer is: Prism = lens power x decentration

The statement that Prism = lens power x decentration is correct as it provides a fundamental relationship in optics when dealing with prismatic effects created by lenses. Prism power, measured in prism diopters, is defined as the displacement of light divided by the distance over which that displacement occurs (the decentration). The formula illustrates that the amount of prism power is directly proportional to both the lens power and the amount that the lens is decentered. When a lens is tilted or decentered from the optical axis, it creates a prismatic effect, bending light and consequently shifting the image. This relationship becomes crucial in optometry and ophthalmic practices, particularly in designing corrective lenses that compensate for misalignment of the eyes, as it guides practitioners in determining how much adjustment to make based on the lens power and the distance from the optical center. Understanding this formula is essential for those involved in vision correction and ensures accurate measurement of prism effects that enhance visual comfort and alignment.