Which instrument is used to check for strain in a lens?

The Colmascope is specifically designed to check for strain in a lens by examining the optical properties and how they may be affected by stress or imperfections within the lens material. This instrument uses polarized light, allowing the observer to detect variations in light transmission that indicate stress patterns, which can lead to optical distortions or visual discomfort for the wearer.

Other instruments, while important in various aspects of vision care, serve different purposes. The Ophthalmoscope is primarily used for examining the interior structures of the eye, such as the retina and optic nerve. The Retinoscope is utilized to evaluate refractive errors by observing the reflex of light off the retina. The Lensmeter measures the prescription of lenses and verifies their optical parameters, but it does not specifically assess the internal strain within the lens material like the Colmascope does.