That means the lens will have a power of about +6.10D for blue light (486.13 nm), +6.00D for yellow-green light (587.56 nm) and +5.90D for red light (656.27 nm). For example a +6.00 lens made of a lens material with an Abbé of 30 will have a dioptric spread of 6 ÷ 30 or 0.2 diopters. Simply divide the power of the lens by the Abbé value of the material. It is quite easy to determine the dioptric spread of any lens material. This difference in power can be called the “dioptric spread” between red and blue light for that particular combination of power and lens material. A lens that measures +5.00, for yellow-green light will measure slightly more than +5.00 for blue light and slightly less than +5.00 for red light. This standardization keeps us all in step when considering the power of lenses. yellow-green (the exact wavelength is 587.56 nm) is used throughout most of the ophthalmic industry for measuring lens power. The amount of slowing (and bending) varies depending on the color (wavelength) of the light passing through the material. Ophthalmic lens materials bend light by slowing it down.
The effects of chromatic aberration result from a combination of the Abbé value of the lens material, the prescription, the point at which the patient’s line-of-sight intersects the lens and the distance from the object being viewed. Much more common comments are, “I can’t see with these,” or “These lenses are just not right.” It’s frustrating to you as an eyecare provider, and disappointing to your patient when aberrations of any kind interfere with the performance of new eyewear. It is rare that a patient will actually mention the colored fringes or “rainbows” caused by chromatic aberration. Pots of gold and bluebirds aside, rainbows are generally unwelcome visitors when it comes to your patients’ spectacle lenses and retinal images. At the end of the rainbow is a pot of gold, and over the rainbow is where bluebirds fly, or so they say.
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