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:Recognized risk factors that may account for the occurrence and severity of radiation retinopathy, especially in cases following low dosages, include diabetes mellitus and chemotherapy.(8,9) Systemic hypertension may also be a risk factor in some cases.
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