Lensmeters

A lensmeter, also known as a focimeter or ophthalmometer, is an optical instrument used by eye care professionals to measure the prescription of eyeglass lenses. It determines the refractive power of a lens, including its spherical power, cylindrical power (astigmatism), and axis. It can also measure the addition power for multifocal lenses and the optical center of the lens.

The basic principle behind a lensmeter involves projecting a target pattern through the lens being measured and then adjusting the focus until the target appears sharp. This adjustment is typically done by moving a lens or mirror within the instrument. The power of the lens is then read from a calibrated scale. Modern lensmeters are often digital, displaying the measurements on a screen, while older models have manual dials and readouts.

Lensmeters are essential tools in optometry and ophthalmology for verifying existing prescriptions, fitting new lenses, and ensuring the accuracy of manufactured eyewear. They help to confirm that a patient's glasses provide the intended visual correction and are crucial for proper dispensing of prescription lenses. The precision of a lensmeter directly impacts the accuracy of the final prescription worn by a patient.