ANSI Z80.1 Mounted Pair Standard – the evolution of US Rx Power tolerances & ISO’s influence

ANSI Z80.1 – 1979 Revision recognizes past standards as being too restrictive for power tolerances use… but why??? Dick Whitney – Chair VCA LTC May 2007  ANSI Z80.1= 1979 adopts simple “real world measurement practice” of tolerancing sphere and cyl only, not principal meridian .13 Tolerance was chosen for practical reasons, given the commonly used RX dispensing interval of.25 Diopters Z

ANSI Z80.1 – 1979 Revision What caused this dramatic change from 1972 to 1979 relaxed tolerances ANSI Z ANSI Z – 0.06 tolerance for glass,.12 plastic (both meridians toleranced) Why else did this important change happen? For the first time, the new 1979 standard reflected what labs could readily measure with digital readout devices which were now on the market.

ANSI Z80.1 – 1979 Revision What caused this dramatic change from 1972 to 1979 relaxed tolerances Reason #1 for the change – Plastic vs. Glass experience? There was no negative feedback from Plastic lens wearers indicating a greater dissatisfaction with their visual acuity as compared with glass RX wearers, in spite of the doubling of the tolerances from.06 to.12 in the 1972 Standard!!!

ANSI Z80.1 – 1979 Revision What caused this dramatic change from 1972 to 1979 relaxed tolerances Reason #2: In March 1978, Dr. George Chase and Ben Lynch published an extensive technical paper was issued in March 1978 titled “ An Examination of Ophthalmic Prescription Spectacle Quality Relative to ANSI Z80.1 – 1972” showing significant problems in meeting this standard.

ANSI Z80.1 – 1979 Revision What caused this dramatic change from 1972 to 1979 relaxed tolerances The 1978 Chase / Lynch conclusions are as important today as they were then : “The most severe problem with ANSI Z as a performance standard is the sheer number of control parameters specified…” “…The absolute number of control parameters must be reduced to a minimum consistent with the safety and efficacy of the device.”

ANSI Z80.1 – 1979 Revision What caused this dramatic change from 1972 to 1979 relaxed tolerances Reason #3 for the change: In 1971, Appleton published a study titled “Ophthalmic prescriptions in half- diopter intervals. Patient Acceptance” Of 126 RX SV wearers studied, there was no statistically significant differences in dissatisfaction rates between.25 Diopter and 0.50 Diopter RX Dispensing intervals.

ANSI Z80.1 Appleton conclusions from.50 Diopter Dispensing study:

ANSI Z80.1 This 1982 Optical World Article referenced the Chase Lynch and Appleton articles and had further interesting observations and conclusions…

ANSI Z80.1 “…for a 99% Recognition rate of the 20/20 Snellen line, the subjects could tolerate a blur range of 0.38 Diopters.”

Why the change in Z ? From 1979 to 1995, the Sph /cyl power tolerances in ANSI Z80.1 reflected real life practice and could be justified from an optical perspective. What happened to complicate matters?

Enter the ISO influence… ISO 1993 J. Redwood

Enter the ISO influence… ISO 1993  In the early 1990’s, ISO was greatly influenced by the EU Consolidation  Significant pressure was placed on speedy adoption of ISO standards  During this time, a study was commissioned by Sola, Vision Ease, and Essilor to fabricate and measure 5 Rx’s in 5 Countries and measure errors

The ISO Double Blind Study… ISO 1993

The ISO Double Blind Study… ISO 1993

The ISO Double Blind Study… ISO 1993

The ISO Double Blind Study… ISO 1993

The ISO Double Blind Study… ISO 1993  Only 10% of the 30 Rx’s met all standards recommendations.  Again we learn that “Setting Standards which are tighter than needed by patients or normally achievable by the manufacturing process causes higher cost to the end user without justification and has legal implications as well.

ANSI reacts to adopt ISO  ANSI Z80.1 – 1995 adopts ISO table for factory finished Rx’s in order to “harmonize with ISO”  A relaxation from.09 to.12 was achieved, but it remained a complex scheme that could only be applied in factories or automated labs.  At the ISO San Francisco Meetings in 1993, this was the compromise achieved for ISO

Why the change in Z ? Dick Whitney – Chair VCA LTC May 2007 In 1995, the OLA issued a 5 page paper describing to their labs how to use this table.

Why the change in Z ? Dick Whitney – Chair VCA LTC May 2007 What was the result? Few labs noticed… But the US press did!!

Why the change in Z ?  In 1997 and 1998, ABC and CBS Television reported on non-compliance issues with ANSI Z80.1, where ~40% did not meet one or more aspects of the 1995 standard and yet:  Quality to the consumer was unchanged.  Customer dissatisfaction was no different, but… …the Standard had changed.

Why the change in Z ?

 As a result, in 1999 ANSI Z80.1 modifies the Standard to tolerance only the higher meridian, but unfortunately does not drop the complex table.  The OLA / VCA conduct a study of 20 labs in 4 geographic locations to measure compliance to ANSI 1999 and what do they find?  29% of RX’s did not fully comply with the standard, with power and cyl axis two of the most significant  And yet, a review of those same RX’s indicated there were no customer returns for patient dissatisfaction!!!

What Next? Dick Whitney – Chair VCA LTC May 2007  Recommendations for the future ANSI Z80.1 revision are now being sought (due August 2007).  Let’s heed the advice that has been a recurring conclusion since 1978: Z “…The absolute number of control parameters must be reduced to a minimum consistent with the safety and efficacy of the device.”  Reinstitute the simple but effective tolerance from 1979: