Ophthalmology

The eye is the perfect organ for ultrasonic examination. It is made up of several tissues delineated by distinct interfaces some of which are curved producing special reflections enabling the operator to obtain an image of the eye, which is easily recognisable.

Most examinations involve scanning across the cornea with the eyelids held open. This avoids the necessity of clipping the hair from the eyelids and eliminates any attenuation of the sound waves by eyelid tissue. Also, the eye itself can be observed during scanning, facilitating the correlation of the ultrasonographic image with the orientation of the globe. In large animals, particularly the horse, there is less hair on the eyelids, and scanning may be performed with the eyelids closed in many cases.

Following the instillation of local anesthetic eye drops, a mound of contact gel is placed upon the cornea. This gel must be viscose to maintain its shape for as long as possible so that it can act as a standoff despite the action of gravity. Probes with a frequency of 7.5-10.0MHz are best suited. A standoff of some form is required when imaging anterior ocular structures, to avoid the reverberation artifact adjacent to the transducer head.