Methods of ultrasound of the eye

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).

When examining the eye, its adnexa and orbit, a certain sequence of sensor placement and direction of the patient's gaze is observed to perform a comprehensive segmental examination of the intraocular structures, taking into account its anterior and posterior sections, as well as division into 4 quadrants (segments) of the eyeball and the presence of a central zone of the fundus. In the orbit, the upper, lower, internal and external sections are distinguished, and the area of the orbital apex is highlighted.

To identify changes in the area of the adnexa of the eye (eyelids, lacrimal gland, lacrimal sac), a general scan is performed in the transverse, longitudinal and oblique planes.

By placing the sensor on the closed upper eyelid above the cornea (transverse scanning), a section of the eyeball is obtained through its anteroposterior axis, allowing one to assess the condition of the central zone of the fundus and the anterior chamber, iris, lens and part of the vitreous body located in the ultrasound beam field, as well as the central section of the retrobulbar space (optic nerve and fatty tissue).

In the future, for a segmental examination of the eye, the sensor is successively installed obliquely:

• from the outside onto the closed upper eyelid, while the patient is asked to move his gaze downwards and inwards, the scanning direction is the same; thus, the lower inner segment of the eyeball and the similar section of the retrobulbar space become accessible for examination;
• on the inner part of the closed upper eyelid (the direction of the patient's gaze and the ultrasound beam is downwards and outwards) - the lower outer segment of the eye and orbit are examined;
• on the inner part of the lower eyelid with the eyes open (direction of gaze and scanning upwards and outwards) - the upper outer segment of the eyeball and orbit is assessed;
• on the outer part of the lower eyelid with the eyes open (direction of gaze and scanning upwards and inwards) - visualization of the upper-inner segment of the eye and the orbit is achieved.

To obtain an image of the rectus muscles of the eye in the retrobulbar space, the sensor is installed as follows:

• to visualize the inferior rectus muscle - on the closed upper eyelid (direction of gaze and ultrasound beam downwards; transverse scanning);
• superior rectus muscle - on the lower eyelid with the eyes open (direction of gaze and ultrasound beam upward; transverse scanning);
• external rectus muscle - with closed eyes at the inner corner of the eye slit (direction of gaze and ultrasound beam outward; longitudinal scanning);
• internal rectus muscle - with closed eyes at the outer corner of the eye slit (direction of gaze and ultrasound beam inward; longitudinal scanning).

In this case, the intraocular structures on the border of the lower segments, upper segments, outer segments, and inner segments of the eye are consistently visible. As with the examination of other organs, the angle of inclination of the sensor must be constantly changed during the examination.

For the organ of vision, the most important role is played by hemodynamically significant changes in blood flow in the ophthalmic artery, superior ophthalmic vein, central retinal artery and vein, posterior short ciliary arteries, as well as in newly formed vessels of tumors and tumor-like foci.

To identify the most important vessels of the visual organ, certain landmarks are used.

The ophthalmic artery (OA) is the main and largest arterial vessel in the orbit, branching off from the siphon of the internal carotid artery, giving rise to an extensive branched network that supplies blood to the soft tissues of the retrobulbar space, including muscles, the eyeball, and the lacrimal gland. Its proximal (initial) part is visualized deep in the central part of the orbit, intersects with the optic nerve and then extends into the superomedial part of the orbit. The immediate continuation of the ophthalmic artery is the supratrochlear artery, emerging from the periorbital region onto the surface of the frontal part of the skull medial to the supraorbital artery. When the ophthalmic artery divides into many branches immediately upon entering the orbit (a “scattered” rather than a “main” type of vessel), difficulties in its identification may arise, but such variants are relatively rare. The ophthalmic artery is most easily identified in the orbit when a sensor is placed using the above-described technique to visualize the lower internal part.

The superior ophthalmic vein (SOV) is the largest vessel of the venous bed of the orbit, and is quite easily detected in the superomedial section with the appropriate positioning of the sensor according to the proposed method. The superior ophthalmic vein is directed from front to back, from top to bottom, partly with an S-shaped bend. Together with the inferior ophthalmic vein, which in some cases may be absent, it drains venous blood into the cavernous sinus.

The central retinal artery (CRA) is a branch of the ophthalmic artery, most easily identified in the optic nerve for about 1 cm from its exit from the eyeball. It is located together with the vein. When mapping, it differs from the latter by its red coloring and arterial type of blood flow. It gives rise to the retinal vessels, branching on the surface of the optic nerve disc.

The central retinal vein (CRV) is an important anatomical structure for the eye, formed by the fusion of the retinal veins, visible as part of the optic nerve at the posterior pole of the eyeball next to the central retinal artery, stained blue with the registration of venous blood flow.

The posterior short ciliary arteries (PSCA) are several branches of the ophthalmic artery (up to 12 in number) located around the optic nerve, piercing the sclera in close proximity to it, and participating in the blood supply to its disc.

Outside the posterior short ciliary arteries on both sides, the posterior long ciliary arteries can be distinguished, which are distinguished by slightly higher blood flow rates; in the area of the equator of the eyeball, with some technical difficulties, there are four vortex veins (two on each side). In the lateral part of the orbit, one of the large branches of the ophthalmic artery is easily visualized - the lacrimal artery, which goes to the lacrimal gland and divides there into smaller branches.

Taking into account the spectral characteristics of blood flow, the arteries of the eye and orbit are classified as vessels of the conditionally peripheral type. The blood flow in them is mono- or biphasic, moderately resistant, with sharp systolic peaks, but with a diastolic component, it never falls below the isoline. In people over 50 years of age, some smoothing of the peaks is noted due to a decrease in the elasticity of the vascular wall.

The venous blood flow spectrum (in the VHV and CVS) is sometimes close to a linear form, and more often it is biphasic, due to oscillations associated with the cardiac cycle. The venous blood flow spectrum in the CVS is usually recorded together with the arterial blood flow in the CAS, but is located below the isoline. The maximum velocity is quite variable: on average from 4 to 8 cm/s in the CVS and from 4 to 14 cm/s in the VHV.

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