What does the prism measurement in a lens indicate?

The prism measurement in a lens indicates deviance in the light path. Prisms are optical devices that can bend light, causing it to change direction. When a lens has a prism measurement, it is designed to alter the path of light that passes through it, allowing for certain corrections in vision.

In optometry, this feature can be particularly useful in addressing issues such as binocular vision problems, where aligning the visual axes of both eyes is essential for proper depth perception and visual comfort. The prism effect can help align the images seen by each eye, ensuring that they are coherent, which is crucial for effective vision.

The other options do not accurately capture the function of the prism measurement. For instance, while corrective power refers to the lens's ability to focus light and correct refractive errors, it does not specifically address light deviation. Weight pertains to how heavy the lens is, which is irrelevant to the prism aspect. Similarly, optical clarity relates to the clarity of vision provided by the lens but does not encompass how the lens influences the light path.