OPHTHALMIC REFERENCE VALUES AND LESIONS IN TWO CAPTIVE POPULATIONS OF NORTHERN OWLS: GREAT GREY OWLS (STRIX NEBULOSA) AND SNOWY OWLS (BUBO SCANDIACUS)

Abstract

This study established ophthalmic reference values and characterized ocular lesions in two captive populations of boreal owls, including 46 eyes of 23 great grey owls (Strix nebulosa) and 38 eyes from 19 snowy owls (Bubo scandiacus). A complete ophthalmologic exam was conducted, including neuro-ophthalmic reflexes, Schirmer tear test I (STT-I), intraocular pressure (IOP) using rebound tonometry, fluorescein staining, horizontal corneal measurements using Jameson calipers, direct and indirect ophthalmoscopy, and ocular ultrasound biometry. Eyes with an STT of <5 mm/min, outliers, and eyes with severe diseases were excluded from reference value analysis. No statistically significant differences were found between right or left eyes in either species or among individuals in different age groups and sexes. Mean intraocular pressures and Schirmer tear tests were also not statistically significantly different between great grey owls and snowy owls (IOP: 9.6 ± 2.6 mm Hg and 9.1 ± 1.9 mm Hg, respectively, and STT-I: 9.8 ± 2.8 mm/min and 9.8 ± 2.4 mm/min, respectively). However, snowy owls overall had a significantly larger eye than did great grey owls, reflected in corneal diameters (23.4 ± 1 vs. 20.0 ± 0.8 mm, respectively) and sonographic biometry. In both species, the most common ocular lesions included keratitis, cataracts, chorioretinal lesions, and abnormal pecten. Establishment of reference ocular parameters will help wildlife veterinarians and rehabilitators determine an appropriate treatment plan and will aid in correctly identifying the presence of ocular disease.

The consequences of avian ocular trauma: histopathological evidence and implications of acute and chronic disease

“…Anterior uveitis (including hyphema) and secondary cataracts are among the most common ocular findings. The avian cornea is relatively spared in traumatic injury in many reports; however, some have reported a relatively high number of corneal abnormalities . Lens displacement is not often reported, perhaps due to the tight attachment of the ciliary processes to the lens annular pad .…”

“…Finally, the posterior segment is often difficult to assess due to opaque media in a traumatized eye. Intravitreal hemorrhage is common, possibly because of bleeding from the vascular pecten . Retinal tear or detachment is a common finding when visualization of the retinal is not obscured by anterior segment or vitreous opacities …”

“…The clinical features of traumatic damage to the avian eye have been characterized . However, most studies evaluating ocular disease birds with suspected trauma have primarily focused on the clinical evaluation of wild and pet birds . Fewer reports of the use of advanced diagnostics have been published (e.g., electroretinogram and B‐mode ultrasound, optical coherence tomography) .…”

Schirmer’s Test I and Determination of Intraocular Pressure in Healthy Common Buzzards (Buteo buteo)

“…The most common method by which to determine tear production is either STT I [3], which is conducted without topical anesthesia, or STT II, which is conducted with topical anesthesia [13]. As in our study, previous studies [1][2][3][4]14] have used STT I as their method by which to determine tear production of wild birds. In a study conducted on 20 common buzzards, STT I values were 12.47 ± 2.66 mm/min [2].…”

Lipoidal corneal degeneration in aged falcons

“…There are few reported cases of nontraumatic, idiopathic corneal disease in raptors . Bilateral idiopathic corneal opacification associated with microcornea has been reported in a Barred owl ( Strix varia ) .…”