It has previously been suggested that the aqueous humour acts as a UV-filter protecting the structures behind. This hypothesis has here been further evaluated by use of spectrophotometry and spectrofluorimetry. Principally three different aspects of the protecting mechanism have been unveiled: absorption, fluorescence quenching and wavelength transformation. The extremely high ascorbate values obviously play a key role in all of them. Thus, aqueous ascorbate both increased absorption and suppressed fluorescence of radiation below roughly 310 nm wavelength. In addition, as a consequence of ascorbate quenching, fluorescence emission to the UV-A range (320-400 nm) is substantially reduced.