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ISO and ANSI Power tolerances vs. “Real world practice”

ISO and ANSI Power tolerances vs. “Real world practice”. ISO and ANSI Power tolerances vs. ”Real World Practice”. What happens in the real world when determining “RX DP power” acceptability?. Record prescribed RX: OD: +.25 = -3.25 x 103. Measure fabricated RX:. Is sphere error > .13?

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ISO and ANSI Power tolerances vs. “Real world practice”

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  1. ISO and ANSI Power tolerances vs. “Real world practice”

  2. ISO and ANSI Power tolerances vs. ”Real World Practice” • What happens in the real world when determining “RX DP power” acceptability? • Record prescribed RX: OD: +.25 = -3.25 x 103 • Measure fabricated RX: • Is sphere error > .13? • Absolute difference is .12, therefore sphere power acceptable • Is cyl error > .13? • Absolute difference is .07 and axis is 103 as prescribed, cyl is acceptable. • Therefore, the lens Passes for power inspection

  3. ISO and ANSI Power tolerances vs. “Real world practice” Now let’s review what Standards authors expect the lab to do: • Shown above is the ISO 8980-1 and proposed “mounted pair” tolerance scheme, also adopted in ANSI Z80.1 -1995 • It was adopted by the ANSI Z80.1 -1995 (US) its first attempt to “harmonize” with ISO Standards • ANSI Z80.1 -1999 dropped each meridian, but still held on to stronger meridian (keeping it almost as complicated)

  4. How does one inspect to comply with the ISO (ANSI Z80.1-1995) Table 1? The lens fails ISO tolerances for a power that is not displayed on the Focimeter, but must be calculated. It is also a failure to ANSI Z80.1 because of strongest meridian error, but few labs ever apply this. It passes the common practice of tolerancing the sphere and cyl.

  5. What would you do? Use this table ? … or do what is practical and ignore the complicated table entirely? Dick Whitney – Chair VCA LTC May 2007

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