Measuring the tear meniscus height (TMH) is easy after fluorescein installation, but the TMH after fluorescein instillation is higher than the TMH before fluorescein instillation. Therefore, we measured the time that the TMH after fluorescein instillation became the same with the TMH, we studied the difference in the TMH between normal eyes and dry eyes. The TMH 0.19 +/- 0.05 mm in the normal eyes and 0.10 +/- 0.04 mm in the dry eyes, and there was a significant difference between the 2 groups. The time that the TMH after fluorescein instillation became the same with the TMH before fluorescein instillation was 2.19 +/- 0.81 min. in the normal eyes and 2.29 +/- 0.73 min. in the dry eyes. Within 4 min. after fluorescein instillation, the TMH became the same with the TMH before fluorescein instillation in all cases and the height persisted until 7 min. after fluorescein instillation. Therefore, measuring the TMH will be easy if it is measured at 4-7 min. after fluorescein instillation.