Required for the correct formation of lens intermediate filaments as part of a complex composed of BFSP1, BFSP2 and CRYAA (PubMed:28935373). Plays a role in maintenance of retinal lens optical clarity (By similarity). {ECO:0000250|UniProtKB:Q6NVD9, ECO:0000269|PubMed:28935373}. This is the function of BFSP2 (beaded filament structural protein 2, ENSG00000170819).