Ultrasound of the eye

The application of ultrasound in ophthalmology with a diagnostic purpose is primarily due to its property to reflect from the boundaries of various tissue structures and, most importantly, to carry information about inhomogeneities in the medium under study, irrespective of their translucency.

The first echograms of the eyeball were published in 1956, and since then, ultrasonic diagnostics in ophthalmology has developed into an independent discipline, using one-dimensional (A) and two-dimensional (B) modes of real-time research, various color Doppler techniques, including using contrast agents, and in recent years the technique of three-dimensional images of the structure of the eyeball and orbit. Ultrasonic studies (ultrasound) in the pathology of the eye and orbit are used extremely widely, since in most cases the only contraindication to their conduct is only a fresh extensive penetrating wound of the eye.

A-mode is characterized by obtaining a series of vertical deviations of the electron beam from the horizontal line (one-dimensional echogram) followed by measuring the time of appearance of the signal of interest from the beginning of the probe pulse and the amplitude of the echo. Since the A-mode is not sufficiently clear and judging the pathological changes in the eye and orbit on the basis of one-dimensional echograms in comparison with the two-dimensional ones is much more difficult, preference in the study of intraocular and retrobulbar structures was given to a two-dimensional image, while the A mode is used mainly , for carrying out ultrasonic biometry and densitometry. Scanning in B-mode has a significant advantage, as it recreates a real two-dimensional picture of the eyeball due to the formation of images by pixels (luminous points) of different brightness due to the amplitude gradation of echoes.

The use of the Doppler effect in ultrasound equipment allowed us to supplement information on structural changes in the eye and orbit with indicators of hemodynamics. In the first Doppler devices, diagnostics was based only on continuous ultrasonic waves, and this caused its lack, since it did not allow differentiating signals that simultaneously emanated from several vessels located at different depths. Pulse-wave Dopplerography made it possible to judge the speed and direction of blood flow in a particular vessel. Most often, ultrasonic dopplerography, not combined with a seroscale image, is used in ophthalmology to assess hemodynamics in the carotid arteries and their branches (ophthalmic, supra-lateral and supraorbital). The combination of pulsed dopplerography and B-mode instrumentation facilitated the appearance of an ultrasonic duplex study, in which both the state of the vascular wall and the registered hemodynamic parameters were simultaneously evaluated.

In the mid-1980s, duplex scanning was supplemented with color Doppler mapping of blood flows, it became possible to obtain objective information about the state of not only large and medium-sized, but even small ones, including intra-organ vessels. From this moment a new stage in the diagnosis of vascular and other pathology began, and the most common angiographic and rheographic techniques have come to the fore. In the literature, the combination of B-mode, Doppler mapping, and pulse-wave Doppler was called triplex, and the method - color duplex scanning (CDS). Since it became available for evaluation of angioarchitectonics of new regions and hemodynamics in vessels with a diameter of less than 1 mm, a triplex study was started in ophthalmology. Publications on the results of Doppler mapping and, later, energy Doppler mapping (EDC) in this field of medicine fell on the 90s of the 20th century and were conducted with different vascular pathology and with suspicion of neoplasms of the organ of vision.

Since in some orbital and intraocular tumors with the help of Doppler mapping, it was not possible to identify the vascular network due to very slow blood flows, in the mid-1990s attempts were made to investigate vascularization with the use of echoes. In particular, noted that with metastatic choroidal carcinoma, contrasting caused only a slight increase in the intensity of the Doppler signal. The use of echocontrast preparations with melanomas less than 3 mm in size did not cause significant changes, and with a melanoma size of more than 3 mm, there was a noticeable signal amplification and the detection of new and smaller vessels throughout the tumor volume. In cases when, after brachytherapy, blood flow was not recorded with Doppler mapping, the administration of a contrast medium did not yield any significant results. In orbital carcinomas and lymphomas, the use of echocontrast marked a distinct or moderate increase in the rate of blood flow and the detection of new vessels. Improved differentiation of the tumor of the choroid from subretinal hemorrhage. It is assumed that color duplex scanning of vessels using echocontrast substances will contribute to a more perfect study of the blood supply of tumors and is likely to largely replace X-ray contrast angiography. However, these drugs are still expensive and not widely used.

Further improvement of the diagnostic capabilities of ultrasound is partly attributed to three-dimensional images (D-mode) of the structures of the organ of vision. Currently, it is recognized that the demand for volumetric reconstruction exists in ophthalmoniccology, in particular, to determine the volume and geometry of uveal melanomas for the purpose of subsequent examination, for example, to assess the effectiveness of the organ-preserving treatment.

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

When mapping the streams of the organ of vision, in most cases, the coding of the arterial channel is reddened, since the blood flow in it is directed towards the sensor, and the venous blood into the blue, due to the outflow of venous blood into the depth of the orbit and further into the cranial cavity (cavernous sinus). The only exception is the orbital veins that anastomose with the veins of the face.

To conduct ultrasound in patients with an ophthalmic profile, sensors with an operating frequency of 7.5-13 MHz, an electronic linear and a microconvex sensor are used, and in the equipment of an earlier release also a mechanical sector scan (with a water nozzle) to obtain a sufficiently clear image of surface structures. The patient is placed in such a way that the doctor is at the head of the patient (as with ultrasound of the thyroid and salivary glands). The examination is performed through the lower or closed upper eyelid (transcutaneous, transpalapebral scanning method).

 Methods of ultrasound examination of the eye 

The parameters of hemodynamics are normally used for comparison with similar parameters in patients with different vascular, inflammatory, neoplastic and other diseases of the organ of vision both in the existing and in the newly formed vascular bed.

The greatest informativity of Doppler techniques was revealed in the following pathological processes:

• anterior ischemic neuroopticopathy;
• hemodynamically significant stenosis or occlusion of the internal carotid artery, causing a change in the direction of blood flow in the basin of the eye artery;
• spasm or occlusion of the central artery of the retina;
• thrombosis of the central vein of the retina, upper eye vein and cavernous sinus;

Ultrasound signs of eye diseases