Chapter 3: LENS FORM

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Anonymous
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244809
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Chapter 3: LENS FORM
Updated:
2013-11-03 21:12:09
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  1. Minus lenses
    two prisms apex to apex spreading light rays diverge light outward as they pass through the lens
  2. plus lenses
    resemble two prisms base to base converging light light rays as they pass through the lens
  3. concave
    inward curve (-)
  4. convex
    outward curve (+)
  5. plano
    a flat or zero curve
  6. cylinder curve
    correct for astigmatism
  7. compound lens or toric
    combines spherical and cylinder curves
  8. lens clock
    These curves on the lens surface can easily be measured
  9. Aspheric lenses
    • defined as lenses that are non-spherical
    • This non spherical surface encompasses all kinds of lenses from aspheric, atoric, progressive, and aphakic.
  10. Atoric
  11. having differing eccentricities for the separate meridians.
    ex.-2.75 -2.00 sphero-cylindrica
  12. Aphakic
    • the absence of the lens of the eye
    • Aphakic lenses use aspherics because plus power lenses higher than +8.00 are outside of the Tersching ellipse and do not have a best form curve. This means that in order to provide the best vision the lens designer has no choice but to use aspherics.
  13. Transposing
    • 1. Add the sphere and cylinder powers to determine the new sphere power.
    • 2. Change the sign of the cylinder.
    • 3. Change the axis by 90 degrees

    • Example:
    • Transpose -3.00 +2.00 x 30
    • 1. Add the sphere and cylinder powers to determine the new sphere power.
    • (-3.00) + (+2.00) = -1.00
    • 2. Change the sign of the cylinder
    • -2.00
    • 3. Change the axis by 90 degrees.
    • 120
    • The transposed prescription is:
    • -1.00 -2.00 x 120

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