What instrument is used to determine the power of a rigid contact?

The instrument used to determine the power of a rigid contact lens is the lensometer. A lensometer, also known as a neutralizer, is specifically designed for measuring the optical power of lenses, including contact lenses. This device utilizes a combination of optics and a light source to assess how the lens refracts light, allowing the practitioner to determine its power in diopters.

In the context of contact lenses, understanding the power is crucial for ensuring the appropriate prescription for vision correction. The lensometer provides accurate readings that help in fitting and prescribing the right type of contact lens to meet the patient's visual needs.

Other instruments mentioned, such as the measuring magnifier, radiuscope, and diameter gauge, serve different purposes. The measuring magnifier is used primarily for visual assessments, the radiuscope measures the curvature of the contact lens, and the diameter gauge is used to measure the physical size of the lens. While these tools are helpful in the overall contact lens fitting process, they do not directly determine the optical power of the lens, which is why the lensometer is the optimal choice for this specific task.