Ultrasound of the eye

The use of ultrasound in ophthalmology for diagnostic purposes is primarily due to its property of being reflected from the boundaries of various tissue structures and, most importantly, carrying information about inhomogeneities in the environment being studied, regardless of their transparency.

The first echograms of the eyeball were published in 1956, and since then ultrasound diagnostics in ophthalmology has become an independent discipline, using one-dimensional (A) and two-dimensional (B) research modes in real time, various color Doppler techniques, including those using contrast agents, and in recent years, a technique for three-dimensional imaging of the structures of the eyeball and orbit. Ultrasound examinations (US) for eye and orbit pathology are used extremely widely, since in most cases the only contraindication to their implementation is a fresh extensive penetrating injury to the eye.

The A-mode is characterized by obtaining a series of vertical deviations of the electron beam from the horizontal line (one-dimensional echogram) with subsequent measurement of the time of appearance of the signal of interest from the beginning of the probing pulse and the amplitude of the echo signal. Since the A-mode does not have sufficient clarity and it is much more difficult to judge pathological changes in the eye and orbit based on one-dimensional echograms compared to two-dimensional ones, preference was given to a two-dimensional image in the study of intraocular and retrobulbar structures, while the A-mode is used mainly for ultrasound biometry and densitometry. Scanning in the B-mode has a significant advantage, since it recreates a real two-dimensional picture of the eyeball due to the formation of an image by pixels (luminous dots) of varying brightness due to the amplitude gradation of echo signals.

The use of the Doppler effect in ultrasound equipment has made it possible to supplement information on structural changes in the eye and orbit with hemodynamic parameters. In the first Doppler devices, diagnostics were based only on continuous ultrasound waves, and this caused its drawback, since it did not allow differentiating signals simultaneously emanating from several vessels located at different depths. Pulse-wave Dopplerography made it possible to judge the speed and direction of blood flow in a specific vessel. Most often, ultrasound Dopplerography, not combined with a gray-scale image, is used in ophthalmology to assess hemodynamics in the carotid arteries and their branches (ophthalmic, supratrochlear and supraorbital). The combination of pulse Dopplerography and B-mode in devices contributed to the emergence of ultrasound duplex research, which simultaneously assesses both the state of the vascular wall and the recorded hemodynamic parameters.

In the mid-80s, duplex scanning was supplemented by color Doppler mapping (CDM) of blood flows, which made it possible to obtain objective information about the condition of not only large and medium-sized, but even small vessels, including intraorgan ones. From that moment on, a new stage in the diagnostics of vascular and other pathologies began, and the most common angiographic and rheographic methods faded into the background. In the literature, the combination of B-mode, Doppler mapping and pulsed-wave Dopplerography was called triplex, and the method was called color duplex scanning (CDS). Since it became available for assessing the angioarchitectonics of new regions and hemodynamics in vessels with a diameter of less than 1 mm, triplex research began to be used in ophthalmology. Publications on the results of Doppler mapping, and later power Doppler mapping (PDM) in this area of medicine occurred in the 90s of the 20th century and were carried out for various vascular pathologies and suspected neoplasms of the visual organ.

Since in some orbital and intraocular tumors it was not possible to detect the vascular network using Doppler mapping due to very slow blood flows, attempts were made in the mid-1990s to study vascularization using echocontrast agents. In particular, it was noted that in metastatic choroidal carcinoma, contrast caused only a slight increase in the Doppler signal intensity. The use of echocontrast agents in melanomas smaller than 3 mm did not cause significant changes, and with melanomas larger than 3 mm, there was a noticeable increase in the signal and detection of new and smaller vessels throughout the tumor. In cases where blood flow was not recorded after brachytherapy using Doppler mapping, the introduction of a contrast agent did not give any significant results. In orbital carcinomas and lymphomas, a clear or moderate increase in blood flow velocity and detection of new vessels was noted with the use of echocontrast. Differentiation of choroidal tumor from subretinal hemorrhage has improved. It is assumed that color duplex scanning of vessels using echocontrast agents will contribute to a more perfect study of tumor blood supply and will probably largely replace X-ray contrast angiography. However, these drugs are still expensive and have not become widespread.

Further improvement of the diagnostic capabilities of ultrasound is partly associated with three-dimensional images (D-mode) of the visual organ structures. It is currently recognized that the demand for volumetric reconstruction exists in ophthalmo-oncology, in particular, to determine the volume and "geometry" of uveal melanomas for subsequent examination, for example, to assess the effectiveness of organ-preserving treatment.

The D-mode is of little use for obtaining an image of the eye vessels. To solve this problem, color and energy coding of blood flows is used, followed by an assessment of the color map and the spectrum of the Doppler frequency shift (DSF) obtained in the pulse Doppler mode.

When mapping the visual organ flows, in most cases the arterial bed is coded in red, since the blood flow in it is directed towards the sensor, and the venous bed is coded in blue due to the outflow of venous blood into the orbit and further into the cranial cavity (cavernous sinus). The exception is the veins of the orbit, anastomosing with the veins of the face.

To perform ultrasound examination of ophthalmological patients, sensors with an operating frequency of 7.5-13 MHz, electronic linear and microconvex, and in earlier equipment also mechanical sector scanning (with a water nozzle), are used, allowing obtaining a fairly clear image of superficially located structures. The patient is positioned so that the doctor is at the patient's head (as in ultrasound examination of the thyroid and salivary glands). The examination is performed through the lower or closed upper eyelid (transcutaneous, transpalpebral scanning method).

Methodology for performing ultrasound of the eye

Normal hemodynamic parameters are used for comparison with similar parameters in patients with various vascular, inflammatory, neoplastic and other diseases of the visual organ, both in the existing and in the newly formed vascular bed.

The greatest information content of Doppler methods was revealed in the following pathological processes:

• anterior ischemic optic neuropathy;
• hemodynamically significant stenosis or occlusion of the internal carotid artery, causing a change in the direction of blood flow in the ophthalmic artery basin;
• spasm or occlusion of the central retinal artery;
• thrombosis of the central retinal vein, superior ophthalmic vein and cavernous sinus;

Ultrasound signs of eye diseases