Objectives: At the conclusion of this conference the resident will have an understanding of the principles of thick lens systems and will be able to define and describe:

• the basic optics of thick lens systems:  2 principal points, 2 nodal points and 2 focal points
• be able to trace light rays through a thick lens system
• be able to calculate vergence and image/object location through a thick lens system
• describe basic clinical applications of a thick lens systems
• the Schematic Eye:  Gullstrand's eye and reduced schema