Contributes to the transparency and refractive index of the lens. May act as a chaperone, preventing aggregation of various proteins under a wide range of stress conditions. Heteropolymer 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). Zinc coordination is achieved at least by His-83, Glu-85 and His-90. His-83 and Glu-85 come from the same molecule within the oligomer, while His-90 residue is provided by another molecule (By similarity). Can also form homodimers and homotetramers (dimers of dimers) which serve as the building blocks of homooligomers (By similarity). 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. Belongs to the small heat shock protein (HSP20) family.