Ophthalmic ultrasonography outlines structures inside the eye and in the eye socket behind it. The socket is called the orbit, the bony space that holds the eye. Ultrasound works from the echo of high-frequency sound waves. Those echoes trace the outlines of ocular and orbital structures. That is why this test can reach a growth sitting behind this man's eye.
The same echoes also measure the distance between structures, which is how eye length is found. Ultrasound helps detect abnormalities such as tumors. It can show a mass's size, composition, and position inside the eye. B-scan ultrasonography gives a two-dimensional picture of ocular and orbital tissue. A-scan ultrasonography sends sound along one line to report positions and distances. Sound waves cannot picture the nerve pathway inside the skull, which is studied with magnetic resonance imaging (MRI) or a CT scan. In an eye with cloudy media, ultrasound may be the only nonsurgical way to see what lies inside. The probe touches the eye, so the technician uses a clean probe tip and a fresh layer of coupling gel each time. The doctor also asks for the eye being examined and the probe position to be written in the chart, so today's study can be compared with the next one.
Think of ultrasound as reaching both the eye and the space behind it. When the doctor needs to know what sits deep in the orbit, sound waves can answer. Knowing what ophthalmic ultrasound can and cannot reach belongs to the diagnostic ultrasound content area of the COA exam.
Incorrect Answers
- A. Sound waves travel well past the front of the eye. Stopping at the cornea and front chamber leaves out the back half of the eye and the whole orbit.
- C. The retina and optic nerve are indeed seen, but this choice leaves out the orbital tissue that the doctor needs checked today.
- D. The pathway inside the skull is beyond the reach of ophthalmic ultrasound. Bone and brain tissue are imaged with MRI or CT instead.
Testing Pearls
- Ophthalmic ultrasonography outlines ocular and orbital structures and measures the distances between them.
- It helps find tumors and report their size, composition, and position.
- A-scan measures distances; B-scan builds a two-dimensional image of eye and orbit.
- With dense media opacities, ultrasound may be the only nonsurgical way to view the inside of the eye.
- Imaging the brain and the visual pathway calls for MRI or CT, not ultrasound.
References
- American Academy of Ophthalmology. Ophthalmic Medical Assisting: An Independent Study Course. Chapter 10, Adjunctive Tests and Procedures.
