[5][6][7] Crystallins are separated into two classes: taxon-specific, or enzyme, and ubiquitous.

Since lens central fiber cells lose their nuclei during development, these crystallins are made and then retained throughout life, making them extremely stable proteins.

Alpha and beta families are further divided into acidic and basic groups.

Seven protein regions exist in crystallins: four homologous motifs, a connecting peptide, and N-terminal and C-terminal extensions.

A chain-terminating mutation was found to cause type 2 cerulean cataracts.