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In order to solve the technical problems of accurate measurement of corneal parameters and effective quality evaluation of ophthalmometers, The National Institute of Metrology (NIM) independently develops a series of standard model eyes with parameters of both radius of curvature and astigmatic axis by using spherical and toric surface design based on corneal surface reflection imaging, and for the first time the physical standard is provided at home and abroad. The radius measurement range is (5.5~10.0) mm and the astigmatic axis range is 0º~180ºwith measurement uncertainty of 0.002 mm and 1ºrespectively with coverage factor of 2. The standard model eyes have been widely used and promoted, supporting the measurement standard establishment for metrological quality inspection institutions in various provinces and cities, effectively solving the test and calibration of human corneal parameter measurement instruments such as the ophthalmometer, thus forming the quantity value transmission and traceability system of the ophthalmometer across the country. In 2020, NIM, as the pilot laboratory, undertakes the national measurement comparison project for the radius verification ability of ophthalmometers which is approved by the State Administration for Market Regulation. A total of 33 laboratories participate in the comparison. Normalized deviation En value is used to evaluate the comparison results. The absolute En values of 33 participated laboratories are all less than 1. The difference between the measurement results and the reference values is within reasonable expectations, and the comparison results are acceptable for each participated laboratory. The measurement comparison results prove that the consistency and effectiveness of the standard model eyes for ophthalmometers is good, and the accuracy and consistency of the measurement results issued by each participated laboratory is effectively evaluated too. Therefore, the accuracy and reliability of the measurement results of ophthalmometers can be ensured.
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