Ординатура / Офтальмология / Английские материалы / Ophthalmic Ultrasound A Diagnostic Atlas 2nd edition_ DiBernardo, Greenberg_2006

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Figure 10–8 Orbital hemorrhage. (A) Transocular transverse B-scan displays an echolucent lesion in the orbit (H) compressing on the globe slightly; note the flattening of the globe wall (arrow).

(B) Transocular longitudinal scan showing the radial extent, from anterior (A) to posterior (P). (C) Standardized A-scan at the orbital setting showing the borders of the clot (bright spots) and the low internal reflectivity (arrow).

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Figure 10–9 Orbital lesions. Lymphangioma following spontaneous hemorrhage. (A) Paraocular transverse scan showing the irregular borders of this large lesion in the anterior portion of the orbit. (B) Paraocular longitudinal scan showing the depth of the lesion (arrow) and a large septum (S) within the lesion. (C) Paraocular A-scan showing the high spikes from multiple septa that were noted within the lesion (S) and the lower reflectivity produced from the hemorrhage within the lesion (arrows).

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Figure 10–12 Adenoid cystic carcinoma. (A) Transocular transverse B-scan shows large, well-circumscribed orbital lesion (L) in the region of the lacrimal gland. Note the indentation of the globe wall (open arrow) and excavation of the orbital bone (arrow).

(B)Longitudinal B-scan image; B, bone; L, lesion; ON, optic nerve.

(C)A-scan shows irregular internal structure and moderate sound attenuation; B, bone; L, lesion; S, sclera.

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Figure 10–13 Cavernous hemangioma (small). (A)

Axial B-scan showing the optic nerve (ON) and the small, round, well-outlined lesion in the muscle cone beneath the nerve (L). (B) Transverse B-scan showing the round, well-outlined lesion (L). (C) Longitudinal B-scan showing the well-outlined lesion (L). (D) Transocular standardized A-scan shows the borders of the lesion (A and P) and the high internal reflectivity (arrow). (E) Standardized A-scan at measuring sensitivity to obtain precise measurements of the thickness of the lesion (double arrow).

A collection of echographic images and findings for unusual or uncommon ocular conditions follows. In addition, we have included a section focusing on biometry for axial length measurements, as well as a brief discussion about the use of laser interferometry (IOLMaster®, Carl Zeiss Meditec, Dublin, CA) to obtain accurate measurements.

Traditional Biometry for Axial Length Measurements and New Technology

Traditional Biometry

We are all aware of the importance of obtaining accurate axial length measurements, as well as achieving reliable intraocular lens calculations, and patient satisfaction plays a major role in determining the outcome of the services we provide. Having a quality control mechanism to evaluate the results is extremely important. One way to increase the chances that the axial length measurements and calculations are appropriate for each patient is to employ a skilled echographer. Whether this person is a physician or a technician, having the ability to identify inaccuracies in the measurements and poor scan quality and knowing when further investigation is indicated are of utmost importance to achieve desirable postoperative results.

The newer generation biometers offer many valuable features and have become increasingly more user friendly, however; the level of knowledge of the person or persons performing these examinations should take precedence over letting the equipment do the work and make the final determinations. There are several things to be considered when performing axial length measurements. The most important is to know the echographic features that indicate a good quality scan.

These include steeply rising, high spikes from the cornea, anterior and posterior lens surfaces, and the retina (indications that the sound beam is aimed perpendicular to each of these structures). In addition, monitoring the anterior chamber depth as a way to minimize corneal compression, looking for the maximal lens thickness and using the longest measurement of a series of good scans obtained at the macula are vital components.

Another factor that will have a significant impact on the final surgical outcome is the proper use of the A-constant, surgeon factor (SF), or anticipated anterior chamber depth constant (ACD), which are provided by the manufacturer of each lens. Studies suggest a close correlation between the various formulas now being used (in eyes of average length) as long as the correct numbers (A-constant, SF, or ACD) are incorporated into the equation.

Using the correct sound velocities is also important. The average speed of sound through the phakic eye is 1550 m/s (meters per second), whereas the velocity through the aphakic eye is slowed to 1532 m/s. Pseudophakic eyes and eyes filled with silicone can also be measured using appropriate sound velocities and most equipment on the market today has been designed with adjustable settings to accommodate the different eye types.

It is recommended that comparison measurements be made between the two eyes and if a difference of 0.3 mm or greater is found, a B-scan screening should be performed. B-scan should also be performed if there is difficulty obtaining perpendicularity to the intraocular structures or if atypical spikes are noted along the vitreous baseline that do not disappear with a change in the sound beam direction.

New Biometry Technology

Suggested Readings

In 2004, partial coherence interferometry (PCI) was introduced as a new way of obtaining accurate axial length measurements. The technique differs from ultrasound in that it uses near-infrared light instead of sound. It does not require contact with the eye and the corneal curvature, anterior chamber depth, axial length, and “white to white” measurements can be automatically obtained in a relatively short amount of time. The equipment is programmed with the most accurate calculation formulas, and calculations can be obtained with a few keystrokes.

Gantenbein CP, Ruprecht KW. Comparison between optical and acoustic biometry. J Fr Ophtalmol 2004;27(10):1121–1127

Haigis W, Lege B, Miller N, Schneider B. Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis. Graefes Arch Clin Exp Ophthalmol 2000; 238(9):765–773

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Figure 11–3 Scleral buckle. It is helpful for echographers to be able to recognize the echographic features of appliances used in the treatment of different ocular pathology. For example, when evaluating an eye with opaque media, a scleral buckle should not be confused with a melanoma. (A) Transverse scan of a 360-degree buckle (arrow). (B) Longitudinal scan of the same buckle (arrow) with the associated shadow (S) produced by attenuation of the sound by the buckle. (C) A-scan showing the highly reflective spike produced by the scleral buckle (arrow) and a decrease in the height of the orbital signals behind the buckle.

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Figure 11–4 Krupin valve. This patient had placement of a Krupin valve to control elevated intraocular pressure. Echographically he had extensive, hemorrhagic choroidal detachments (arrow). The valve was working and a large bleb could be identified (B).