Editing Corrective lens (section)

== Vertex distance ==
[[Vertex distance]] is the space between the front of the eye and the back surface of the lens. In glasses with powers beyond ±4.00D, the vertex distance can affect the effective power of the glasses.<ref>{{cite book|last=Schwartz|first=Gary S.|title=The Eye Exam: A Complete Guide|url=https://books.google.com/books?id=vNwHSXEXYmkC|year=2006|publisher=SLACK Incorporated|isbn=1556427557|page=62}}</ref>  A shorter vertex distance can expand the field of view, but if the vertex distance is too small, the eyelashes will come into contact with the back of the lens, smudging the lens and causing annoyance for the wearer. A skilled frame stylist will help the wearer select a good balance of fashionable frame size with good vertex distance to achieve ideal aesthetics and field of view. The average vertex distance in a pair of glasses is 12-14mm.  A contact lens is placed directly on the eye and thus has a vertex distance of zero.