What instrument is primarily used to measure the base curve of a contact lens?

The instrument primarily used to measure the base curve of a contact lens is a radiuscope. This device is specifically designed to analyze the curvature of the contact lens surface. The base curve is critical for achieving the proper fit of the lens on the eye, as it mirrors the curvature of the cornea to ensure optimal vision and comfort. The radiuscope provides precise measurements, which are essential for fitting contact lenses correctly and ensuring that they align well with the eye's surface.

While the keratometer is used to measure the curvature of the cornea itself, making it useful in assessing eye topography, it does not directly measure the base curve of the lens. The lensometer, on the other hand, is utilized for measuring the prescription of spectacles and contact lenses, such as verifying their power, but it does not provide accurate measurements of the base curve. The ophthalmoscope is an instrument used for examining the interior structures of the eye and is unrelated to measuring lens curvature. Understanding the specific purpose of each instrument reinforces the importance of choosing the correct tool for measuring the base curve in contact lens fitting.