What is the term for the distance from the anterior surface of the eye to the back surface of the spectacle?

The term for the distance from the anterior surface of the eye to the back surface of the spectacle is known as vertex distance. This measurement is important in optics and lens fitting since it affects the effective power of the lenses in relation to the wearer's eye. A proper vertex distance ensures that the optical axis of the lens coincides with the visual axis of the eye, optimizing visual clarity and comfort.

Pupillary distance refers to the distance between the centers of the pupils in each eye, which is critical for accurately positioning lenses in glasses but does not describe the physical distance from the eye to the lens surface.

Optical center distance is related to how the optical centers of the lenses align with the line of sight but is not a term specifically used for the distance in question.

Frame drop describes how low the frames sit on the nose in relation to the eyes but is not a measurement related to distance from the eye to the lens. Thus, vertex distance is the most appropriate term for the distance from the eye to the back surface of the spectacle.