Ocular ultrasound (synonyms: ocular sonography; ocular ophthalmography) is a commonly used procedure in ophthalmology (eye care) for the diagnosis of optically invisible changes, especially in the anterior portion of the orbit. Although other imaging modalities, such as computed tomography (CT) or magnetic resonance imaging (MRI), have been continuously developed and the fields of application of these additional imaging modalities have multiplied, classical sonography represents the gold standard (1st-choice examination method).
Indications (areas of application)
- Ablatio retinae (synonyms: amotio retinae; retinal detachment).
- Hyposphagma – sharply limited hemorrhage from conjunctival vessels under the conjunctiva; bleeding into the eye prevents a view of internal structures of the eye by means of a slit lamp or ophthalmoscope
- Cataract (cataract – clouding of the lens with vision reduction) before planned surgery. Here, the A-mode of ultrasound is used to calculate the axial length of the eye and the refractive power of the artificial lens to be used.
- Tumors such as: the orbit (myosarcomas, lipomas, liposarcomas, tumors of the nervous tissue and glandular tissue) and the retina (retinoblastoma, retinal angiomas, adenocarcinomas of the retinal pigment epithelium).
The procedure
Ultrasound examination (sonography) is an imaging procedure that has become a standard medical procedure due to the absence of radiation exposure, ease of performance and outstanding cost-benefit ratio. The principle of ultrasound is the emission of high-frequency sound waves from a transducer (pen-like probe), which are reflected differently due to the heterogeneous composition of the various tissue surfaces and are received by the probe. A computer then creates a two-dimensional representation of the examined tissue from the images. In this regard, there are the following imaging methods of sonography:
- A-mode (amplitude modulation) – a display method used today only in exceptional cases. The measured and reflected waves are displayed starting from a zero line.
- B-Mode (Brightness-Mode) – with the help of this display mode, a sectional image of the eye tissue is created (this is the usual display method).
Special forms of ocular sonography are:
- Doppler sonography and duplex sonography – with the two procedures, it is possible to visualize circulatory disorders in the eye.
- Ultrasound biometry – measurement of the individual structures of the eye, which can be used to prepare for cataract surgery.
On the procedure of ocular sonography:
- Before starting the ultrasound examination, local anesthesia (anesthesia) of the eye is performed by the doctor, if sonography through the eyelid is not meaningful. Eye drops are used as anesthetic (drug for anesthesia).
- Following the possible anesthesia, a gel with a high water content is applied to the eye to reduce the reflection of sound waves.
- Thereupon, the transducer is held directly on the eye so that there is no air between the gel and the transducer, otherwise the reflection would be amplified and this would lead to a reduction in the validity of the examination.
- The doctor now asks the patient to look in different directions. At the same time, the examiner must change the probe position regularly.
Advantages of ultrasound examination are:
- There is a higher resolving power in sonography of the eye compared to CT or MRI.
- Furthermore, there is no need for contrast injection as in angiography (the imaging of the vasculature by injection of a contrast agent and subsequent application of diagnostic imaging techniques such as X-ray), nor for radiation exposure as in the use of CT. On the basis of this, the option for arbitrary repeatability of diagnostics is implementable.
- In addition, a view of both the muscle-associated movement processes and the flow processes in the blood vessels in real time and in vivo (in the living body) becomes feasible.
- Not only the lack of invasiveness compared to CT and MRI is an argument for the use of sonography, but also the cheaper price of the examination speaks for the use of ultrasound in ophthalmic diagnostics.
Disadvantages of ultrasonography are:
- As a result of physical limitations, the diagnosis of the eye by sonography is limited to the anterior two orbital thirds. Furthermore, pathologic processes extending retroorbitally (lying behind the bony orbit) are better visualized by MRI.
- Due to the possibility of an increased number of artifacts due to, for example, increased interactions with the tissue under examination, the diagnostic value is limited when examining certain areas of the eye.
Possible complications
- Although this is a completely non-hazardous procedure, there is a possibility that accompanying problems such as corneal damage may occur due to the placement of the transducer.
The use of ultrasound on the eye is a low-complication and highly informative diagnostics for the detection of various diseases and for monitoring the progress of already manifested diseases. Moreover, the procedure is recognized and used worldwide, ensuring a high standard of examination.
