Journal of Clinical and Experimental Ophthalmology
Open Access

Abstract

The Additional Diagnostic Value of Optical Coherence Tomography (OCT) and Its Application Procedure in A Wide Variety of Avian Species

Panagiotis N Azmanis, Franziska G Rauscher, Beatrice Werner, Jens Huebel, Christian Koch, Wencke Vetterlein, Nicole Körber, Jens Thielebein, Andreas Reichenbach, Peter Wiedemann, Mike Francke and Maria-Elisabeth Krautwald-Junghanns

Objective: The current study introduced OCT as a novel tool in clinical veterinary ophthalmology in a much wider variety of free-living avian species than hitherto studied.
Methods: OCT was tested and performed in 39 free-living birds (21 species of 12 families) and compared to direct ophthalmoscopy. Birds were examined with combinations of different restraints (manual restraint or fixation on a holding device) and different anaesthesia regimes (none, sedation, general anaesthesia). Inter- and intra-species specific variations of the general procedure, the restraint methods and the clinical findings were evaluated.
Results: OCT was possible in all examined avian species (from 40 g up to 7720 g) and superseded direct ophthalmoscopy in quality and quantity of ophthalmological findings. All restraint methods enabled OCT examination, however combination of general anaesthesia and a holding device provided the most rapid and subjectively the least stressful examination technique. Stability, stress reduction, head angle and distance from the OCT device were important factors influencing volume scanning quality. Sixteen, out of 39 birds, presented ocular abnormalities detected by OCT (compared to only five birds when using direct ophthalmoscopy). OCT with included fundus images offered an objective assessment of retinal changes. Retinal abnormalities included changes of fundus pigmentation, drusenoid changes and severe retinal and choroidal degenerations. Species-specific variations of retinal layer dimensions and of foveal structures were evident.
Conclusion: OCT is a promising, non-invasive method, which significantly compliments standard techniques. OCT is applicable to a wide variety of avian species; it provides high quality cross-sectional images of the retina, enabling accurate and improved diagnosis and prognosis of therapies. An assessment of the visual capabilities of traumatised birds is a major factor for their rehabilitation and survival in the wild. Finally, this method is an excellent tool in interdisciplinary retinal research, providing novel insights into the diversity of very specialized structural adaptations of avian retina.