Certified Ophthalmic Assistant Practice Exam

What is the term for the distance from the cornea to the back surface of the spectacle lens?

1. Vertex distance

2. Optical center distance

3. Pupil distance

4. Focal length

The correct answer is: Vertex distance

The term for the distance from the cornea to the back surface of the spectacle lens is known as vertex distance. This measurement is crucial in ensuring that spectacles provide the correct optical correction to the wearer. Vertex distance helps in aligning the corrective lenses with the patient's line of sight, which can significantly affect visual acuity and comfort. Understanding vertex distance is especially important for individuals who require a high degree of corrective power, as variations in this distance can lead to differences in the effective power of the lenses. Accurate measurement ensures optimal vision correction and aids in the proper fitting of eyewear. The other terms, while related to vision care, do not specifically refer to this measurement. Optical center distance typically refers to the distance between the optical centers of the lenses, pupil distance is the measurement from one pupil to another, and focal length refers to the distance of the focal point to a lens, which is a concept more related to the lens itself than to its positioning relative to the eye.