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:MP measurements were obtained with a modified confocal scanning laser ophthalmoscope (mpHRA, Heidelberg Engineering, Heidelberg, Germany) [20] using autofluorescence images obtained at two excitation-wavelength based on the pioneering work of Delori et al.
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