The eye can be further examined with ultrasound, employing the same principles used in fetal ultrasound, although on a smaller scale. The sound delivered is reflected at different tissue interfaces and the reflected beam is received by the transducer. The reflected sound waves are analyzed to give further information about ocular structures. The transducer itself may be placed directly on the eye, after topical anesthesia, or on the eyelid, depending on the desired procedure.
A-scan ultrasound is necessary as part of the preoperative evaluation for cataract surgery, as the axial length of the eye must be determined to properly calculate the necessary intraocular lens power for any given eye. It may also give useful information on certain types of intraocular tumors.
B-scan ultrasound displays a 2-dimensional image of the internal structures in the eye, allowing for evaluation of the retina when it is obscured by media opacities, such as occurs with dense cataract and vitreous hemorrhage. It is also useful in the evaluation of ocular tumors and a variety of other ocular disorders.