In 30 healthy volunteers the tear-film break-up times of both eyes were determined, comparing one eye with a cut-off filter (customarily used in fluorescein angiography (Schott OG 530, thickness 3 mm] with the common method, not using this filter, in the other eye. By using the filter the variance of observed break-up times is decreased, and the time elapsing after the administration of the dye no longer influences the break-up time significantly. The filter described here is therefore recommended for determining the tear-film break-up time.