Prism by Decentration

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...

Understanding Prism Thinning

The curvature of a progressive addition lens surface gradually increases toward the bottom of the lens, becoming increasingly steeper. This increase in curvature (and surface power) is what produces the add power of the progressive lens. Unfortunately, because the...

Methods for Estimating Lens Thickness

Often, it is beneficial for the eye care professional to predict the finished thickness of a pair of spectacle lenses. Determining the change in thickness that results from the patient's use of a different frame or lens style is a common example.Patients investing a...

Basic Refraction Procedures for Opticians

Many opticians around the country have shown great interest in learning the procedures involved but have been unable to take a course on the subject. This article is designed to introduce the subject to those interested, and to provide some continuing education to...