Education

Understanding Prism Thinning

Posted by on May 25, 2010 in Surfacing | 0 comments

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 bottom of the lens is steeper than the top of the lens, the upper edge of a progressive lens blank is thicker than the lower edge. Understanding Prism Thinning (pdf) by Darryl...

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Methods for Estimating Lens Thickness

Posted by on May 25, 2010 in Surfacing | 0 comments

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 considerable amount of money into thinner and lighter lenses want to know just how thin their new lenses will be. This is a question that often strikes fear in the hearts of unprepared opticians. Those armed with the knowledge required to provide the answer, however, quickly earn the respect of their patients. Even these...

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Basic Refraction Procedures for Opticians

Posted by on May 5, 2010 in Refracting | 7 comments

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 former refraction students. Refraction is defined as the act of determining the focal condition (emmetropia or various ametropias) of the eye and its corrections by optical devices, usually spectacles or contact lenses (Keeney, et al, 1995, p. 254). Many opticians around the country have shown great interest in learning the...

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The Electromagnetic Spectrum

Posted by on May 5, 2010 in Lens Form and Theory | 0 comments

Produced by the nuclear cauldrons of stars and all matter in the cosmos, energy in the form of electromagnetic radiation permeates our entire universe. Every second of every day we are bombarded with and surrounded by electromagnetic radiation; some bounces off of our bodies, some passes through us, and some we absorb, but most goes undetected and unperceived. Electromagnetic energy travels at the speed of light (2.9×10^8 m/s or 180,000 miles/sec) in the form of a wave. In fact, we classify electromagnetic energy according to its wavelength. Wavelength is defined as the distance...

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Lens Power

Posted by on May 5, 2010 in Lens Form and Theory | 1 comment

As light rays pass through a lens with power, the rays are bent or refracted. In a lens with a plus power, the light rays converge or are refracted toward one another. The point at which the light rays converge is called the focal point and in a plus lens, is behind the lens surface. In a lens with a minus power, the light rays diverge or are refracted away from one another. If these rays are extrapolated or traced back toward the light source, the lines will converge and form a focal point in front of the lens surface. The lens power is relative to the focal distance or the distance...

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Lens Form: Sphere, Cylinder, and Axis

Posted by on May 5, 2010 in Lens Form and Theory | 3 comments

It can be helpful to think of very basic lens forms in terms of prisms. Recall, as light passes through a prism it is refracted toward the prism base. Minus lenses therefore resemble two prisms apex to apex spreading light rays outward as they pass through the lens, while plus lenses resemble two prisms base to base converging light rays as they pass through the lens. Of course, most lenses are not comprised of angular prismatic surfaces but consist of curved surfaces. The most basic of these curves is a sphere. The curve on the surface of a spherical lens, if extrapolated in all...

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