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A.R. Wegener, U. Kaspers, M. Edingloh; Optical Coherence Tomography of the Ocular Fundus in Dogs and Cats – Advantages and Limitations With Regard to Ocular Safety Studies . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3312.
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Optical coherence tomography was investigated with regard to its suitability for early detection of morphological changes in the ocular fundus of dogs and cats in toxicity studies.
Beagle dogs and cats of mixed breeds from professional breeders were chosen as animal models. Optical coherence tomography was performed with the Stratus OCT® (Carl Zeiss) in a dark room. For the ocular examination, dogs were anaesthetized with Ketamin (5 mg/kg bw), Xylazin (1 mg/kg bw), diazepam (1 mg/kg bw) and cats with Ketamin (10 mg/kg bw), Xylazin (2 mg/kg bw). All animals received 0.5 % atropin eye drops for induction of mydriasis and were placed on a special holder infront of the optics. An assistant opened the lids and aligned the eye to the optics of the instrument. A series of measurements covered the papillar region and retinal areas on both sides of the optic disk. The morphological analyses were performed with the instrument’s software. All care and handling of the animals was in accordance with the German Tierschutzgesetz and the ARVO Declaration for the Use of Animals in Ophthalmic and Vision Research.
The accessability of the eye depended on the proper performance of anaesthesia. Deep anaesthesia induced prolaps of the third lid and disorientation of the eye. Mild anaesthesia did not eliminate the saccadic movements. The optic disk of the beagle dog was more irregularly shaped than that of the domestic cat which had a regular shape inspite of the mixed breeds. In the dog, the tapetum lucidum extended towards the outer rim of the disk margin whereas in the cat it extended towards the inner rim of disk cavity. Retinal thickness was higher in cats than in dogs, independent of the area of measurement. Drying of the ocular surface rapidly deteriorated the signal, evidenced by the colour saturation of the tomogram.
The instrument proved to be suitable for measurement of morphological changes the fundus on cats and dog without any modification of the optics and software. Data acquisition could be performed reproducibly provided a trained assistant oriented the animals head. Abnormal features of the ocular fundus like albinism or a tigroid tapetum and changes in retinal thickness could be characterized. Changes in diameter of retinal vessels or geometry of the optic disk could be reproducibly measured over time with a high sensitivity and low background noise. The technique proved suitable for detection of retinal changes in toxicity studies.
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