Certified Ophthalmic Assistant Practice Exam

Which device measures the power of spectacle lenses?

1. Sphygmometer

2. Lenticular gauge

3. Keratometer

4. Lensmeter

The correct answer is: Lensmeter

The lensmeter, also known as a lensometer, is specifically designed to measure the optical power of spectacle lenses. It works by determining the focal length of the lens and calculating its dioptric power. When a lens is placed in the lensmeter, it produces a series of markers and measurements that correspond to the lens's prescription, allowing eye care professionals to verify the accuracy of the lenses. Having a precise measurement of the power of spectacle lenses is crucial for ensuring patients receive the correct vision correction. This device is essential in both optical laboratories and clinics for checking prescription accuracy before dispensing eyeglasses. In contrast, other devices listed have different primary functions. A sphygmometer is used to measure blood pressure, a lenticular gauge is used for measuring thickness of lenticular (magnifying) lenses, and a keratometer is designed for measuring the curvature of the cornea, primarily for fitting contact lenses rather than measuring spectacles. Therefore, while they are valuable tools in ophthalmic practice, they do not perform the specific function of measuring the power of spectacle lenses as the lensmeter does.