Zum gegenwärtigen Stand der Ultraschalldiagnostik des Auges und der Orbita

Zusammenfassung

Das Auge ist als echographisches Untersuchungsobjekt besonders geeignet. Nach Anpassung der Geräte und Schallköpfe an die relativ kleinen Abmessungen gelangen daher schon sehr früh vielfältige, zuverlässige differentialdiagnostische Entscheidungen. Bald wurde erkannt, daß die diagnostischen Kriterien in den Echogrammen durch gerätetechnische Parameter verfälscht werden können. Zur Aufdeckung solcher Fehlerquellen und zur Sicherstellung optimaler, reproduzierbarer Untersuchungsbedingungen wurden Meßtechniken zur Prüfung und Kalibrierung der Geräte und Schallköpfe entwickelt - lange bevor ähnliche meßtechnische Vorschläge von der International Electrotechnical Commission veröffentlicht wurden.

Heute werden für die echographische Darstellung des Auges und der Orbita schnell abtastende, elektromechanische B-Bild-Verfahren in Kombination mit A-Bild-Verfahren benutzt. Mit meßtechnisch überprüften Geräten und Schallköpfen (Gesamtempfindlichkeit, Arbeitsfrequenz und Frequenzspektrum, Schallfeldgeometrie usw.) können vielfältige diagnostische Entscheidungen zuverlässig getroffen werden.

Längen- und Distanzmessungen hoher Genauigkeit sind hilfreich zur Beurteilung des axialen Linsendurchmessers bei linsenbedingtem Glaukom. Die Messung der Achsenlänge des Auges ergibt ein zusätzliches Kriterium zur Verlaufsbeurteilung der Hydrophthalmie; in Verbindung mit der Messung anderer Durchmesser erlaubt sie die genaue Lokalisation von Fremdkörpern. Die Ultraschall-Exophthalmometrie dient der exakten Differenzierung von Pseudoprotrusio und echter Protrusio bulbi.

Innerhalb des Bulbus kann man unter Berücksichtigung von Arbeitsfrequenz, Gesamtempfindlichkeit und resultierenden Echoamplituden Glaskörpertrübungen, Fibrinmembranen, Fremdkörper, primäre (exsudative) Netzund Aderhautablösungen und Tumoren erkennen und voneinander differenzieren. Hierzu werden auch die Lokalisationsbeziehungen der pathologischen Strukturen und ihre Ortsveränderungen nach Bulbusbewegungen herangezogen.

Abstract

The eye and orbit offer particularly suitable conditions for diagnostic ultrasonography. Hence, versatile and successful differential diagnoses were obtained early, after the apparatus and transducer probes had been adapted to the eyes relatively small dimensions. It was soon evident that the diagnostic criteria could be falsified by technical parameters of the equipment used. Measurement techniques for the control and calibration of apparatus and transducer probes were developed in order to discover such sources of error and to ensure optimum, reproducible conditions of examination. This was long before similar suggestions of measurement technique had been published by the International Electrotechnical Commission.

Today, electro-mechanic real-time scanner are preferred for B-scanning of the eye and orbit, in combination with A-scanning. Equipement and transducer probes which had been subjected to checking and control procedures (especially in respect of sensitivity, working frequency and frequency spectrum as well as beam shape) will enable a multitude of reliable diagnostic decisions. High-accuracy length and distance measurements prove helpful to determine the axialdiameter of the lens in lens-induced glaucoma. Measurement of the axial length of the eye yields an additional criterion to assess the course of buphthalmos cases; in combination with measurements of other diameters, foreignbody localisation can be performed more accurately. Ultrasound exophthalmometry (a combination of Hertel's opticexophthalmometry and ultrasound axial length measurements) can help in arriving at a reliable differentiation of pseudo-protrusion and genuine Protrusion of the eye.

Within the eye itself (in respect of working frequency, sensitivity and resulting echo amplitudes) it is possible to detect vitreous opacities, fibrin membranes, foreígn bodíes, primary retinal and choroidal detachments and tumours, which can then be differentiated from one another. Location of the pathologic structures and their movements after changing the direction of glance, are also taken into consideration in differential diagnosis.

Circumscribed and diffuse space-occupying lesions can be identified in the orbit. Cysts are reliably differentiated from tumours; in certain tumour types, further differentiation can be achieved, e.g. in cavernous haemangioma. Penetration of the orbital wall by a tumour can be recognized. Sound attenuation in the lesion area, the echo amplitude of structures behind the lesion, movements of the lesion area as the direction of glance changes, will yield further information; this also applies to echogram changes during compression of the lesion area by the transducer probe or following Valsalva's manoeuvre or jugular vein compression. Further developments will concentrate on properly calibrated equipment and computerized echo Signal evaluation. The technical Parameters which offer best possibilities of arriving at a reliable diagnosis in a particular disease will be worked out. The manufacturers are facing an increasing demand for calibrated and correctly declared apparatus and transducer probes, For evaluating more of the information contents of echo Signals, e.g. phase shifts and frequency spectrum alterations, computer-assisted echogram analyses are in the course of being developed; in certain cases they can already be applied in clinical diagnosis.

X-ray computerized tomography is additionally applied in many cases. The different information obtained by means of both these methods, especially when their evaluation is combined, will yield more relevant diagnostic information than if one of these techniques is used alone.