How low can we get? Tonometry in the Thomson gazelle (Gazella thomsoni)

Purpose: To establish a normal reference range of intraocular pressure estimates in Thomson gazelles (Gazella thomsoni). Materials and Methods: Applanation tonometry was conducted in 22 eyes of 11 gazelles anesthetized for transportation purposes with a mixture of etorphine hydrochloride and acepromazine maleate. Five sequential readings using a Tono-Pen XL (Mentor Ophthalmics, Inc., Norwell, MA) were obtained from each eye. Results were analyzed for the effect of age, weight, gender, side, and replicate readings and were compared with estimates in other species. Results: Mean (± standard deviation) intraocular pressure estimate in 22 eyes of 11 gazelles was 7.6 ± 1.6 mm Hg. None of the variables tested had a significant effect on the results. Conclusions: To date, the intraocular pressure estimates in the Thomson gazelle are the lowest reported in any species.