prism reference point Taken from from http://www.zeiss.com web site: For a progressive power lens or semifinished lens blank, that point on the front surface stipulated by the manufacturer at which the prismatic effect of the finished lens is determinde. NOTE: The prism measured is the resultant of prescribed prism and prism thinning. The following excerpt…

In 1621, a Dutch physicist named Willebrord Snell (1591-1626), derived the relationship between the different angles of light as it passes from one transperent medium to another. When light passes from one transparent medium to another, it bends according to Snell’s law which states: that the angle of refraction is related to the angle of…