Background: D-β-Aspartic acid residues, which are biologically uncommon, have been reported to accumulate in various proteins of the living body with age. In the present study, D-β-aspartic acid-containing proteins were found to be localised in pingueculae, which represent one of the most prominent age-related ocular changes.Methods: Surgical specimens of conjunctivae with or without pingueculae were obtained from eight patients. Immunohistochemical localisation of D-β-aspartic acid-containing proteins was performed using a polyclonal antibody against D-β-aspartic acid-containing peptides.Results: Strong immunoreactivity to D-β-aspartic acid-containing peptides was detected in the subepithelial amorphous materials of all surgical specimens with pingueculae. In contrast, no immunoreactivity to D-β-aspartic acid-containing peptides was detected in the specimens without pingueculae.Conclusions: Pingueculae are thought to be aggregates of proteins that contain D-β-aspartic acid residues. It is known that the conversion of L- to D-aspartyl residues is accelerated by ultraviolet irradiation. In addition, D-β-aspartic acid-containing proteins, in general, tend to aggregate with each other and accumulate in the tissues. These facts indicate that ultraviolet irradiation-induced racemisation of aspartic acid is closely related to the development of pingueculae
