Ultrasonographic and Computed Tomographic Examinations of the Avian Eye: Physiologic Appearance, Pathologic Findings, and Comparative Biometric Measurement

Abstract

Ultrasonography (US) and computed tomography (CT) were performed after routine ophthalmologic and ophthalmoscopic examinations in 190 eyes of six various diurnal (common buzzard [Buteo buteo L., 1758], n = 20; common kestrel [Tinnunculus tinnunculus L., 1758], n = 20) and nocturnal raptor species (barn owl [Tyto alba L., 1758], n = 22; tawny owl [Strix aluco L., 1758], n = 8; long-eared owl [Asio otus L., 1758], n = 5; horned owl [Bubo bubo L., 1758], n = 1); and domestic pigeons (Columba livia, Gmel., 1789; n = 19), with a total of 95 individuals. Pathologic findings such as lens subluxation and luxation, intravitreal hemorrhage, detached retina, post-traumatic partial sequestration, or malformation of the pecten could be demonstrated with diagnostic imaging tools, while opacities of cornea or lens constrained direct ophthalmoscopic examination. The results proved US to be a quick noninvasive imaging technique for detailed ocular diagnoses. CT provided detailed information of the bony skull and bony scleral rings as well as adequate visualization of shape, size, and margination of the eye and lens. Nevertheless, CT was unable to differentiate subtle structures within the vitreous like the pecten oculi or hemorrhage. Biometric measurements were carried out to objectify imaging results. Results showed good correlation of depth and width of the anterior eye chamber, lens and vitreous, length of the bulbus, and the pecten but no correlation of cornea and posterior wall thickness was found.

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

“…Ocular abnormalities noted (per number of eyes) in this species included mature cataract (1), anterior capsular incipient cataract (1), suspected vitreal blood clots (1), and chorioretinal lesions (13). Multifocal brown-black, small spots at the base of the pecten were seen in 13 eyes and were suspected to be chorioretinal lesions.…”

“…2). 6,13,30 Therefore, previous normal pecten biometry and blood flow obtained with ocular ultrasound can aid in determining the integrity of the pecten after trauma and thus may help in determining prognosis. The pecten is thought to nourish the retina and control the pH of the vitreous; therefore, damage to the pecten could potentially result in retinal changes.…”

“…Ocular ultrasonography has previously been demonstrated 13,14,21,30 to be an effective, safe, and noninvasive technique for evaluation of the avian globe. Ultrasonography is especially beneficial when intraocular examination is not possible as a result of corneal edema, hyphema, cataracts, or vitreous hemorrhage.…”

Diagnosis of Retrobulbar Round Cell Neoplasia in a Macaroni Penguin (Eudyptes chrysolophus) Through Use of Computed Tomography

“…In a study comparing ultrasonographic and CT examinations of the avian eye, the authors evaluated the usefulness of both imaging modalities for complete ocular examination with the goal of determining the best way to evaluate avian eyes when routine ophthalmoscopic examination was deficient, for instance in cases of corneal opacification. 24 The study included 95 birds, including domestic pigeons and several individuals from each of six raptor species. On ultrasound, the scleral ossicles were described as hyperechoic stripes that caused distal shadowing and complicated accurate measurement of the globe diameter.…”

Comparison of Computed Tomographic Images of Birds Obtained With Sedation vs General Anesthesia

“…Several studies have been published on the normal tomographic and CT anatomy of birds. [1][2][3][4][5][6][7] Digital radiography is an important imaging technique used for avian patients; however, there are limitations associated with traditional radiography, including the following: (1) general anesthesia is usually required during radiographic procedures owing to the temperament of birds and the difficulties associated with manual restraint, and (2) radiographic evaluations are an insensitive means of detecting pathology in areas with significant superimposition of anatomic structures. 8 One scientific study compared conventional radiographs with CT in imaging of the head in both raptors and psittacines.…”