Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:5 D or more in some situations.(21,22) The tolerance for position error for toric andmultifocal IOLs is even less, so small amounts of tilt, decentration, or rotation of these IOLs can result in significant deviations from the desired refractive outcome as well as symptomatic visual aberrations.
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