OBJECTIVES

Ultrasonography is a safe noninvasive way to evaluate the intraocular and retrobulbar tissue of opaque eyes. A-mode, two-dimensional and Doppler ultrasonography have been used to characterize the ocular biometry, ocular structures and orbital and ocular vasculature respectively, in humans and dogs. In rabbits the biometry of normal eyes have been reported by A-mode. However, in the author's knowledge the ocular examination by two-dimensional and Doppler imaging ultrasonography has been poorly documented. The purpose of this study was to describe the normal ultrasonographic appearance of rabbits eyes using two-dimensional ultrasound, perform biometric evaluation and study the orbital and ocular vasculature using duplex Doppler ultrasonography.

MATERIALS

This study was performed in 20 adult New Zealand White rabbits weighing between 3 and 3.5 kg. All animals were considered normal on the basis of complete physical and ophthalmic examinations. The ophthalmic examination consisted of slit-lamp biomicroscopy, indirect ophthalmoscopy and tonometry. Ultrasonographic examination was performed using a Philips P 800 machine with a 7.5 MHz linear array transducer. The ultrasonographic procedure and the interpretation of the images were achieved according literature data. By two-dimensional ultrasonography the following ocular structures were measured: cornea, anterior chamber, lens thickness, vitreous body and anterior to posterior dimension of the globe. By duplex Doppler ultrasonography ocular and orbital vessels were identify and blood flow measurements, including peak systolic velocity, end diastolic velocity, pulsatility index and resistive index, were obtained in external ophthalmic artery and ciliary arteries.

RESULTS

On two-dimensional images rabbits eyes appeared as well-defined ovoid structures. The identified ocular structures showed similar appearance to those reported in dogs. Because of there was not significant difference between the biometry of the both eyes, the measurements of the ocular structures are the mean and standard deviation of 40 eyes. They are the following: cornea, 0.48±0.07 mm; anterior chamber, 2.17±0.27 mm; lens thickness, 6.66±0.26 mm; vitreous body, 6.59±0.37 mm; and anterior to posterior dimension of the globe, 15.72±0.39 mm.

By color Doppler imaging ciliary arteries and veins, external ophthalmic artery and dorsal external ophthalmic vein were easily identified. Blood flow measurements were not significant different between left and right eyes. Mean and standard deviation were the following in external ophthalmic artery: peak systolic velocity, 30.50±7.75 cm/sc; end diastolic velocity, 17.9±4.80 cm/sc; pulsatility index, 0.56±0.16; and resistive index (0.41±0.08). In ciliary arteries the results were the following: peak systolic velocity, 17.33±4.00 cm/sc; end diastolic velocity, 11.43±2.91 cm/sc; pulsatility index, 0.43±0.11; and resistive index, 0.34±0.07.

CONCLUSION

This study will provide baseline information for further clinical investigations of ocular abnormalities in rabbits with an ultrasound machine available to the veterinarian.