Research on new test lenses for dioptric power of intraocular lenses

Abstract

Intraocular lenses are intended to replace the cataractous human lens when it is surgically removed. All intraocular lenses are labelled with dioptric power in aqueous. Whether the labelled value is exact is very important for both patients and doctors. Therefore, verification of the accuracy and calibration of the instrument used to measure intraocular lens dioptric power are of the utmost importance. However, in China there hasn't any normative test or calibration methods suggested to check these instruments, and so do any standards or regulations. The objective of this research is to realize the calibration of these instruments and unify the quantity value of intraocular lens dioptric power by developing a new set of test lenses. According to the definition of intraocular lens dioptric power, first spherical aberration for different design structures is analyzed in air and in aqueous respectively. Then the optimum design structure is chosen and test lenses are manufactured. Next paraxial approximation is used to relate the lens parameters with dioptric power and uncertainty budget is calculated. Finally experiments are done on different kinds of instruments and discussions are made. The newly developed test lenses are composed of 8 pieces of lenses with dioptric power from -10 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> to 30 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in the step of 5 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The uncertainty of the standard value is about 0.06 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with coverage factor 2. Results show that the test lenses can realize the calibration of different kinds of instruments used to measure intraocular lens dioptric power very well. A new set of test lenses for dioptric power is designed and manufactured for intraocular lens instruments. Its quantity values can be traced to the highest National Standard in China. Moreover, by experiments it is proved to be feasible and effective to realize metrological calibration of IOL power instruments. The research is also helpful to the establishment of metrological standard for intraocular lens dioptric power in China.