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

The distance from the anterior surface of the eye to the back surface of the spectacle is referred to as vertex distance. This measurement is critical in the fitting of corrective lenses, as it directly affects how the prescription is realized in practice. If the vertex distance is incorrect, the glasses will not properly align with the eyes, potentially leading to visual discomfort or inappropriate correction of vision.

Understanding vertex distance is essential for ensuring that the optical center of the lenses aligns with the wearer's line of sight. This alignment is vital because any discrepancy can lead to distortion or blurriness, undermining the effectiveness of the lenses. Other terms listed, such as pupillary distance, focal length, and lens thickness, relate to different aspects of vision correction and eyewear fitting but do not specifically define the space measured from the eye to the lens.