Contributes to the transparency and refractive index of the lens (By similarity). Acts as a chaperone, preventing aggregation of various proteins under a wide range of stress conditions (PubMed:20440841). Required for the correct formation of lens intermediate filaments as part of a complex composed of BFSP1, BFSP2 and CRYAA (By similarity). Heteromer composed of three CRYAA and one CRYAB subunits (By similarity). Inter-subunit bridging via zinc ions enhances stability, which is crucial as there is no protein turn over in the lens (By similarity) (PubMed:20440841). Can also form homodimers and homotetramers (dimers of dimers) which serve as the building blocks of homooligomers. Within homooligomers, the zinc-binding motif is created from residues of 3 different molecules. His-100 and Glu-102 from one molecule are ligands of the zinc ion, and His-107 and His-154 residues from additional molecules complete the site with tetrahedral coordination geometry (PubMed:20440841). Part of a complex required for lens intermediate filament formation composed of BFSP1, BFSP2 and CRYAA (By similarity). Translocates to the nucleus during heat shock and resides in sub-nuclear structures known as SC35 speckles or nuclear splicing speckles. Acetylation at Lys-70 may increase chaperone activity. Undergoes age-dependent proteolytical cleavage at the C-terminus. Belongs to the small heat shock protein (HSP20) family.