An overview of the electromagnetic spectrum including: gamma rays, ultraviolet, visible light, infrared, and radio waves.

Lens power is proportional to the angle light is refracted as it passes through a lens.

A discussion of spherical and cylinder lens forms.

Depending on the equipment used by the doctor, a prescription may be in plus or minus cylinder form. For surfacing, the lab uses the minus form, meaning if a prescription is written in a plus cylinder form it must be transposed before processing.

An optical prism can be thought of as a wedge. The wider portion of the wedge is referred to as the base and the narrower portion is referred to as the apex. As light passes through the prism the light rays are bent toward the base. Consequently, when viewing objects through a prism the objects appear to be displaced in the direction of the apex.

Normally, eyeglasses are fitted with the optical center of the lens directly in front of the eye. If the lens is fit off-center, image displacement can occur due to induced prism. The higher the power or the further the lens is fit off-center, the higher is the induced prismatic effect.

Download the printable resultant prism chart, handy for converting the two-component prescriber's method of specifying prism to a single component resultant method.

Primer on lens materials and their properties

Industry studies have shown that approximately 70% of all spectacle wearers receive a cylinder correction for astigmatism. Further, 50% of these wearers have corrections with over 0.50 D of cylinder power. This article will show that conventional lens design does not adequately address the peripheral optical performance of lenses with cylinder power. Moreover, it will explain how new atoric lens designs can provide superior optical performance for all patients�including those with astigmatism.