I see about two to three a year, and virtually all had to travel the long road to find a solution for their visual distress.
The 3rd edition of 'System for Ophthalmic Dispensing' discusses and gives examples of Remole's equations for bicentric grinding (slab-offs).
http://journals.lww.com/optvissci/Fu..._Ocular.9.aspx
http://journals.lww.com/optvissci/Fu...ies__a.13.aspx
Bookmarks