Intraocular Pressures in Free-Ranging Eastern Screech Owls (Megascops asio), Great Horned Owls (Bubo virginianus), and Barred Owls (Strix varia) Measured by Rebound Tonometry.

Free-ranging, nocturnal raptors are frequently presented to wildlife centers due to trauma, and ocular trauma is a common finding in these cases. Measurement of intraocular pressure (IOP) is a critical part of an ophthalmic examination; however, reference values for comparison are lacking in nocturnal species. Rebound tonometry was used to measure IOPs of normal eyes from free-ranging, nocturnal raptors (eastern screech owls [Megascops asio], great horned owls [Bubo virginianus], and barred owls [Strix varia]) presented to a wildlife rehabilitation center. In total, 248 eastern screech, 105 great horned, and 70 barred owl eyes were evaluated in this study. All IOP measurements were collected using a rebound tonometer on the "d" setting while owls were restrained in an upright position. The mean IOP for eastern screech owls was 9.22 ± 3.98 mmHg and 9.35 ± 3.47 mmHg for the right and left eyes, respectively, with a combined mean of 9.28 ± 3.76 mmHg. The mean IOP for great horned owls was 12.71 ± 6.16 mmHg and 12.86 ± 6.62 mmHg for the right and left eyes, respectively, with a combined mean of 12.78 ± 6.35 mmHg. The mean IOP for barred owls was 10.41 ± 4.37 mmHg and 10.97 ± 4.72 mmHg for the right and left eyes, respectively, with a combined mean of 10.66 ± 4.51 mmHg. Intraocular pressure results did not differ significantly between the right and left eyes for any species. These normal values will provide clinicians reference ranges for comparison and allow more accurate screening for ocular pathology.