Tolerance and absence of rebound vasodilation following topical ocular decongestant usage.

Commercial preparations of two topical ophthalmic vasoconstrictors were evaluated for whitening ability, duration of action, tolerance, and rebound vasodilation in 11 normal volunteers. Both 0.02% naphazoline HCI and 0.05% tetrahydrozoline HCI significantly reduced baseline redness after a single use (Part I); however, naphazoline produced significantly more whitening than did tetrahydrozoline. Only naphazoline retained its whitening ability after ten days (Part II). The level of redness remained significantly below baseline for eight hours after a single use of either vasoconstrictor and for six hours after multiple use of naphazoline. The diminished effectiveness of tetrahydrozoline after the ten-day test period may encourage its overuse. Neither vasoconstrictor produced rebound vasodilation after discontinuation of use.