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To use synthesized onion lachrymatory factor (SOLF) to investigate age-related changes in reflex-tear secretion and ocular-surface sensation. We separated 91 healthy volunteers into four groups: groups A, age 20–29 years; B, 30–39; C, 40–49; and D, older than 50 years. We exposed one eye of each subject to SOLF and measured the elapsed time until the subject’s limit of irritation tolerance (TLI) was reached and an increase in the tear meniscus radius (ΔR). After the SOLF stimulus, corneal sensitivity was examined by Cochet-Bonnet esthesiometry (CB), and reflex-tear secretion was examined by the Schirmer I-test (ST). TLI was significantly shorter in group A than in the other groups ( P < 0.0001), and the groups B and D also differed significantly from each other ( P = 0.0013). The increase in ΔR was significantly greater in group A than in group C ( P = 0.0306) or D ( P < 0.0001), and groups B ( P = 0.0002) and C ( P = 0.0308) also differed significantly from group D. There were no significant intergroup differences in the CB and ST results. An age-related decrease in reflex-tear secretion and ocular-surface sensation was revealed by the SOLF test but could not be detected by either CB or the ST. [ABSTRACT FROM AUTHOR]