Optical coherence tomography as a diagnostic tool for retinal pathologies in avian ophthalmology.

Purpose: Optical coherence tomography (OCT) is an established diagnostic tool for retinal pathologies in human eyes and has been adapted to small animal models. However, there have been only a few attempts to use OCT for examination of avian eyes, and little is known about structural details of healthy or pathologically affected retinas in living birds.

Methods: We used SD-OCT (high-resolution spectral domain OCT) to investigate eyes of various avian species including birds of prey. The birds were anesthetized by isoflurane application during OCT examination. Eyes of a common buzzard (Buteo buteo) could be used for a comparative analysis of OCT images and histologic/immunohistochemical examinations.

Results: We investigated 45 wild and domestic birds (25 different species, 40 g-7.7 kg body mass) without and with diverse pathologic indications (e.g., body or head trauma). Animals were generally and ophthalmologically examined, and the diagnostic findings of direct ophthalmoscopy and OCT were compared. The OCT examination revealed an increased number of animals with clinical findings and allowed a detailed assessment of structural changes in retinal and choroidal tissue compared to simple direct ophthalmoscopy. Common findings were retinal and choroidal degeneration, retinal detachment, choroidal schisis, drusen, and drusenoid changes. Histologic and immunohistochemical analysis of retinal tissue confirmed the findings of the OCT examination.

Conclusions: Spectral domain OCT of eyes in living birds is applicable and useful as a diagnostic tool in veterinary clinical practices and for vision research in general. Optical coherence tomography improves the quality of the common assessment methods in avian ophthalmology, and expands the diagnostic possibilities with respect to identification and prognosis of diseases. This will be particularly important for hereditary retinal defects, especially of precious breeding individuals, or estimation of treatment success in traumatized wild birds with the aim of release back into the wild.