Tear Film Stability and Tear Break Up Time (TBUT) in Laboratory Rabbits-A Systematic Review.

Several older studies on rabbits indicated that the pre-corneal tear film was unusually stable and this perspective was revisited recently. However, the methods used for these studies were very different from those generally used in human studies. A literature search was undertaken for the time period of 1965 through 2017, mainly using PubMed, to identify studies where values for the tear break up time (TBUT) were reported for the eyes of nominally normal (healthy) laboratory rabbits regardless of breed or age and where the methods were more similar to those routinely used in human clinical studies. For 20 reports identified where sodium fluorescein was used, the average TBUT values in any particular study ranged from 1.9 to 51 s, with a group mean of 21.8 ± 11.9 s (SD), with the inter-study variability in TBUT (as the coefficient of variation) being 19.4%. For four studies not using fluorescein, the mean break up time reported was 32.7 ± 16.2 s, while a separate study (also not using fluorescein) reported an average break up time of 1788 s. Most reports of the pre-corneal tear film stability in laboratory rabbits, especially as reported over the last 10 years, indicate break up times of less than 60 s have been observed, although has been little consistency in the methods used. Overall, this outcome is not consistent with a perspective that the rabbit (as routinely used in experimental studies) has an extraordinarily stable tear film.