Ultrasound for Vets, by Dr.Kishor Mahind---Eye

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The Eye:

2-D real time USG of the eye has been used to diagnose intra-occular conditions, such as retinal detachment, intra-occular masses, foreign bodies, anterior and posterior luxation of lens, cataract etc when the opacity of the anterior segment precluded examination of deeper structures within the eye and has been used to diagnose retrobulbar abnormalities. Real time mechanical sector scanner with 7.5 or 10.0 MHz transducer can be used. There are two methods of examination of eye. In one technique, transducer can be placed on the eyelids. This rarely gives a satisfactory image. Other method widely used is placing the transducer directly over the cornea. Examination of eye is well tolerated by dogs and cats as well. If the eye is painful it is advisable to instill a few drops of topical local anaesthetic first. The commercial acoustic gels are not irritant to the cornea. Image the eye in both vertical and horizontal planes of section, swinging the beam up and down and from side to side to ensure that whole area is examined. After examination of eye, the gel was removed by careful irrigation of the eye with sterile water.

Normal appearance: The globe of eye is anechoic and smoothly rounded in shape the lens is rarely seen clearly as its curved surfaces tend to scatter the reflected sound away from the transducer, but small bright echoes may be seen where the lens is perpendicular to the incident sound beam. The retina, choroid, sclera are not seen as separate layers, but as a single, smooth echogenic wall. A bright spot may be seen caudo-medially representing the optic disc. The retrobulbar tissues are composed of fat, which is quite echogenic, and extra-ocular muscles, which are relatively hypoechoic. The retrobulbar tissues form an orderly cone, within which the hypoechoic track of the optic nerve may be sometimes identified.

Abnormal findings: If the lens is cataractous, it is much more delineated than normal, with a thick and continuos echogenic border. The vitreous liquefies during vitreous degeneration; however the liquefaction is variable within the vitreous cavity, resulting in tissue with different acoustic impedances. Therefore multiple echogenic lines or areas will be seen (Alexandra van der Woerdt et al). Retinal detachment is seen as a thin line ballooning into the vitreous from the posterior wall of the globe. If the detachment is complete, then a typical appearance of "seagull's wings" is seen, with points of attachments as the optic disc and the ciliary body. During B-mode USG, a waving motion of the detached retina was often seen. Intra-ocular masses are readily seen as they are highlighted by the anechoic vitreous.

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