This ongoing study is investigating the effects of confirmation bias and document readability on user document relevance judgments in interactive information systems. Preliminary results from a within-subjects eye-tracking experiment suggest a significant interaction between document readability and the level of confirmation bias on user engagement during the relevance evaluation process. Higher readability has been found to enlarge the disparity in reading efforts between relevant and irrelevant documents. Users with higher level of confirmation bias need to engage more attention when evaluating relevance. These initial findings help to elucidate these dynamic relationships and provide insights that could help refine user interface design for more effective and unbiased human information interaction.