IOL registry and errors in A-scan.
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Humans↗
Biomedical subjects
N E Norrby
Publications and source records attributed to N E Norrby.
Determining the imaging quality of intraocular lenses.
PURPOSE: To validate the proposed optical requirements of a draft international standard for intraocular lenses (IOLs). SETTING: Eight optical testing laboratories in the United States, Germany, Japan, and The Netherlands. METHODS: The testing laboratories performed modulation transfer function (MTF) tests on various IOLs using a model eye and visual resolution tests in air. Each laboratory performed duplicate measurements on a set of 43 lenses that was circulated among the testing laboratories. RESULTS: The interlaboratory tests showed that the MTF measurements using a model eye had better repeatability and reproducibility than the more common industry practice of resolution testing in air with parallel light and the United States Air Force three-bar target. However, the two methods correlated well. The commonly applied criterion that an IOL resolve in air at least 60% of the Rayleigh cutoff spatial frequency corresponded to a minimum requirement of 0.43 MTF units at 100 mm-1 in a model eye. CONCLUSIONS: Either criterion may be applied in accordance with a proposed international standard for IOLs. The model eye method can be applied over a broader range of dioptric powers and is relevant for materials that interact with aqueous. Both tests appear to have a greater ability to detect unwanted surface aberrations than resolution testing of IOLs in a water cell using parallel light, a method described in the current American National Standards Institute standard.
Diagnostic Techniques, Ophthalmological↗
Prediction of intraocular lens power using the lens haptic plane concept.
PURPOSE: To test algorithms for the preoperative estimation of the lens haptic plane (LHP) and to assess these in terms of predictability of postoperative refraction. SETTING: S:t Erik's Eye Hospital, Stockholm, Sweden. METHODS: Preoperative axial length, anterior chamber depth (ACD), and cataractous lens thickness were measured in consecutive cases scheduled for phacoemulsification and posterior chamber intraocular lens (IOL) implantation. The algorithms tested used ACD and cataractous lens thickness to estimate LHP. The exact geometry of the IOL was used to calculate postoperative ACD from LHP. Thick lens theory and paraxial ray tracing were used to calculate predicted postoperative refraction. The calculated value was compared with actual refraction 3 to 6 months postoperatively. RESULTS: Mean absolute average error in predicted refraction was 0.38 diopters (D), with 78% of eyes within 0.50 D and 97% within 1.00 D for the best algorithm. CONCLUSIONS: The predictability in postoperative refraction found by applying the LHP concept and paraxial ray tracing was excellent. However, the small sample, with its unusually slight variation in axial lengths, did not allow statistically significant differences between different postoperative refraction prediction methods to be demonstrated.
Aged↗
Accuracy in determining intraocular lens dioptric power assessed by interlaboratory tests.
PURPOSE: To describe a testing program conducted by a standards group as a guide for setting international tolerances for intraocular lens (IOL) dioptric power. SETTING: Multicenter study. METHODS: Seven biconvex, poly(methyl methacrylate) IOLs ranging in power from 10.00 through 30.00 diopter (D) were circulated among nine participating laboratories experienced in IOL optical measurements. Each laboratory performed repeated optical tests to determine dioptric power. These results were analyzed for repeatability and reproducibility in accordance with methods specified by the International Organization for Standardization. RESULTS: Intralaboratory repeatability was less than 0.5% of the dioptric power, and interlaboratory reproducibility, when following a normalized procedure for correction and conversion, was less than 1.0% of the dioptric power. CONCLUSION: Tolerance limits of +/0 0.30 D in the range 0 to 15.00 D, +/- 0.40 D for 15.50 to 25.00 D, and +/- 0.50 D for 25.50 to 30.00 D have been proposed as an international standard for IOLs. The contribution of IOL power error within the limits of the standard are estimated to contribute less than 1.0% to the total error in postoperative refractive prediction.
Lenses, Intraocular↗