| Popis: |
MTF data can be a dependable criterion for assessing the performance of an optical system if the testing is done under conditions that closely resemble the actual application. For testing IOL performance, this requirement can be met by inserting the lens in a suitable eyes model. A dynamic eye model in which the corneal power can be varied to simulate the range of conditions found in different human eyes is ideal, but if the vergence angle is chosen carefully, a fixed eye model can be sufficient. For the resulting MTF data to be valid, it is necessary to consider the entire spread function of the system. In the case of a multifocal IOL, the failure to accurately sample the complete spread function is a major source of measurement errors. The detector must be able to characterize in considerable detail the central maximum of the in focus segment. At the same time it must also deal with the complex and diffuse `halo' from the out of focus segment of the lens. Additionally, it must be able to measure the stray light found beyond the halo, that results from the transitions between the various zones of the multifocal lens. Test systems based on the direct measurement of MTF have a substantial advantage in these cases where the spread function is large and complex. |
